Wood e book by PG Designs

CONSTRUCTION CANADA WOOD DESIGN

Wood Design

A look at cutting-edge engineered wood products and projects

Published by Kenilworth Media Inc. 15 Wertheim Court, Suite 710 Richmond Hill, Ontario L4B 3H7 Toll-free: 800-409-8688 (905) 771-7333; Fax: (905) 771-7336 www.constructioncanada.net

The information and contents in this publication are believed by the publisher to be true, correct, and accurate, but no independent investigation has been undertaken. Accordingly, the publisher does not represent or warrant that the information and contents are true, correct, or accurate, and recommends that each reader seek appropriate professional advice, guidance, and direction before acting or relying on all information contained herein. Opinions expressed in the articles contained in this publication are not necessarily those of the publisher.

Contents Part One The Advent of Cross-laminated Timber

By David Moses, PhD, P.Eng., PE, LEED AP, and Sylvain Gagnon, Ing.

Part Two Designing for Timber-framed Buildings

By Matthew Reid, MASc., P.Eng., and Cory Zurell, PhD, P.Eng.

Part Three Trees in the Tower

By Jim Taggart, FRAIC

Part Four Specifying Modern Timber Connections

By Maik Gehloff, Dipl.-Ing. (FH), M.A.Sc.

Part Five Restoring Historical Architectural Woodwork in the Construction Industry By Alan Stacey and Kathy Stacey, B.Sc.

CONSTRUCTION CANADA WOOD DESIGN

Part One The Advent of Cross-laminated Timber

BY DAVID MOSES, PHD, P.ENG., PE, LEED AP, AND SYLVAIN GAGNON, ING.

David Moses, PhD, P.Eng., PE, LEED AP, has been involved in over 200 structural engineering projects in Canada and the United States. He spent 10 years working for Equilibrium Consulting (Vancouver and Toronto) before founding Moses Structural Engineers in 2010. Moses has specialized in timber engineering and natural building materials for nearly 20 years; he is the 2009 recipient of the Wood Engineering: Advocate award from WoodWORKS! Ontario for his work in designing and promoting the use of wood products. He sits on several of the Canadian Standards Association (CSA) code committees in the forest products sector. Moses can be reached via e-mail at dmoses@mosesstructures.com. Sylvain Gagnon, Ing., is a scientist with FPInnovations’ Building Systems division. He joined the Forintek team in 2003 as a research scientist and structural engineer. Gagnon is experienced in wood design, as well as in the industrial manufacturing and standardization of structural wood products. He worked for numerous years as project leader in consulting engineering for SNC-Lavalin, Pellemon, and Tecsult. Gagnon also participated in the start-up of a Québec-based engineered wood plant and held, for four years, a position of engineering instructor at Université Laval. He was also a member of the Standing Committee on Structural Design of the National Building Code of Canada (NBC) from 2005 to 2010. Gagnon can be contacted by e-mail at sylvain.gagnon@fpinnovations.ca.

CONSTRUCTION CANADA WOOD DESIGN

Photo courtesy FPInnovations

The Advent of

Cross-laminated Timber A relatively new technology is poised to significantly change the way Canadians design and build with wood framing. Cross-laminated timber (CLT) panels, specified in Europe for more than a decade, are now manufactured in Canada.1

CONSTRUCTION CANADA WOOD DESIGN

The Austria House (Whistler, B.C.) features the first Canadian application of cross-laminated timber (CLT) panels for roof and floor structure and diagonally dowelled solid wood panels for the wall structure. Photo courtesy APG Austrian Passive House Group, www.oesterreichhaus.at

CLT panels are large prefabricated wall and floor assemblies used in various building types for residential and non-residential projects. Assembled in a platform-frame fashion, the effect is comparable to suspended concrete slabs spanning between loadbearing concrete walls to resist gravity and lateral loads. These wood panels can also be used in combination with post-and-beam wood frame or steel frame components. Vertically oriented panels can enclose a building, similar to tilt-up concrete construction, while the horizontally oriented panels span across beams to create the floor plates. Another option, sometimes employed for industrial buildings, involves balloon-frame construction. The method takes advantage of the large dimensions of CLT products by hanging floors assemblies from multi-storey wall panels.

CLT 101 As cross-laminated timber panels were developed in Europe over a long period, there are many companies who make a wide variety of panel types. The products can be manufactured up to approximately 3 x 18 m (10 x 60 ft) and then cut to size for each project. They are normally produced in thicknesses from about 50 to 400 mm (2 to 16 in.), but thicker panels are available.

CONSTRUCTION CANADA WOOD DESIGN

CLT panels can be assembled in platform-frame fashion, like concrete slabs suspended between load-bearing walls. Images courtesy FPInnovations

The laminates making up the panels are pieces of dimension lumber (e.g. 1x4s and 1x6s, or 2x4s and 2x6s) that are either glued using radio-frequency presses or fastened to each other. The lumber is stacked in its flat orientation into layers of three, five, seven, or more on a forming bed and then subjected to uniform pressure using hydraulic or vacuum presses. The outer layers tend to use higher-grade lumber for strength and appearance, while lower-grade material can be for the transverse layers. Each layer is perpendicular to the adjacent ones (hence the term â&#x20AC;&#x2DC;cross-laminatedâ&#x20AC;&#x2122;). This means when the lumber in each layer tries to expand or contract due to shrinkage or swelling, the others restrain any movement. This contributes to the superior dimensional stability of the CLT panel. After pressing, completed CLT panels are moved onto a computer numerical controlled (CNC) cutting machine to trim the edges and plane, sand, or wire-brush the faces. The automated machines drill out the panel for connection hardware and cut openings for windows, doors, stairs, and mechanical chases. The use of CNC technology allows accurate, efficient cutting and profiling of conventional solid and glue-laminated wood products. CLT panels can be thought of as high-performance products prefabricated under controlled conditions, but they are not generic, assembly-line lookalikes. Fully detailed models of the panels allow designers to customize layouts and window and door openings.

CONSTRUCTION CANADA WOOD DESIGN

FPInnovationsâ&#x20AC;&#x2122; CLT Handbook aims to serve as a technical resource for Canadian design/ construction professionals who will be using the wood technology for the first time.

After the design is complete, and once the CLT components have been determined for each project, the cutting patterns can be optimized to reduce waste. Any material cut away from the panel can be collected as wood waste and reused in other ways by the manufacturer (as opposed to conventional, field-built assemblies where site waste must be carefully separated and sent away for reuse or recycling at added cost). Quality control in the plant is much better than in the field, and the controlled environment eliminates temperature and humidity cycles, while offering protection from water, snow, and ultraviolet (UV) light. Once assembled onsite, the joints are tightâ&#x20AC;&#x201D;this results in cleaner surfaces for attaching building envelope components. Construction time onsite is significantly reduced as work becomes assembly rather than carpentry. Panels up to 18 m (60 ft) long and 3 m (10 ft) wide can be used in single elements to simplify installation. The short construction cycle has immediate effects on project costs. It also means CLT panels are exposed to the elements for less time as the roofing and cladding can be installed much faster. Unlike concrete, CLT panels do not require additional protection and heating to cure in cold weather. Additionally, the relatively light weight of the panels reduces the need for heavy lifting equipment onsite.

Material strengths Cross-laminated timber panels have unique environmental, architectural, structural, thermal, and fire resistance properties and benefits. In Europe, architects have long recognized wood has a lower carbon footprint than other conventional building

CONSTRUCTION CANADA WOOD DESIGN

While there are quite a few CLT manufacturing plants in Europe, the first Canadian facilities are expected to open shortly.

materialsâ&#x20AC;&#x201D;wood harvesting and processing takes very little energy and the material itself is a carbon sink. The architects who use CLT panels are able to offset the total carbon usage in the manufacturing of the material, construction, and operation of their buildings to make them effectively carbon neutral. Interior panels can be left exposed as a finish without additional materials (at the discretion of the designer and depending on fire code requirements and the needed acoustic performance). In North America, low- and medium-quality lumber and standing dead timber killed by mountain pine beetles (MPBs) can provide a good resource for CLT manufacture. Programmatically, the panels lend themselves well to repetitive, shallow floor plates for mid-rise and high-rise buildings. However, they can just as easily be adopted for single-storey or low-rise construction. In North America, CLT lends itself well to making more liveable cities through neighbourhood densification and mid-rise wood construction. Acoustic performance for sound transmission between walls and floors is fairly good with CLT panels due to their solid mass. Additional sound insulation through a variety of tested European techniques has led to floor systems with STC ratings over 65 dB with careful detailing between walls and floors, and at stairwells. The thermal mass of CLT panels gives them some ability to moderate temperature. Working as a component of a building envelope system, panelized construction leads

CONSTRUCTION CANADA WOOD DESIGN

This CLT manufacturing plant uses a radio-frequency press.

to tighter building envelopes with blower door tests resulting in very low air exchanges per hour. In a traditional wood frame wall assembly, airflow is controlled using an air barrier approach with sealed polyethylene, airtight drywall, sealed sheathing, or a sealed sheathing membrane. In a CLT panel wall assembly, the most practical strategies for creating a continuous air barrier are either a sealed exterior sheathing membrane or interior airtight drywall. Fire performance of massive wood members is recognized in building codes for heavy timber construction, but CLT is not yet specifically mentioned. In Europe, studies have shown CLT panels exposed to fire will form a char layerâ&#x20AC;&#x201D;this protects the rest of the panel, allowing it to retain strength and dimensional stability. Unlike conventional construction, solid wood products mean less risk of fire spread through gaps or voids in the building components. Structurally, CLT panels have strength and stiffness in- and out-of-plane that make them suitable for gravity and lateral load resistance. The excellent axial resistance and in-plane shear resistance of cross-laminated timber allows its use in load-bearing and shear wall construction. The outer layers are oriented to take advantage of the longitudinal tension and compression properties of lumber and to act as bending members for floors and tall walls. CLTâ&#x20AC;&#x2122;s in-plane strength and stiffness are also beneficial when panels are used as floor and roof diaphragms. In seismically active regions, this can be a significant improvement over conventional framing and systems made with other materials.

CONSTRUCTION CANADA WOOD DESIGN

The laminates that make up the panels are pieces of dimension lumber (e.g. 1x4s and 1x6s, or 2x4s and 2x6s). They are either glued using radio-frequency presses or fastened to each other. The lumber is stacked in its flat orientation into multiple, odd-numbered layers on a forming bed and then subjected to uniform pressure using hydraulic or vacuum presses.

Ductility (i.e. energy absorption) is provided through metal connections. For multistorey construction, the lighter weight of wood walls compared to concrete and masonry can result in smaller footing sizes, saving cost and materials. Connections between wall and floor panels and to other building components are available via proprietary fasteners or customized options. Other benefits of the material include vastly reduced construction waste (due to the efficiency of prefabrication), and ease of attachment of services, such as electrical conduit, sprinkler lines, and plumbing systems. In Europe, CLT panels compete against concrete and masonry construction where impact drills must be used to attach pipe hangers. This can be labour-intensive and yield joint damage or injuries to workers. Attaching to wood is much simpler and does not require impact drills.

Moving forward FPInnovations is a not-for-profit group that includes members of the forest operations, wood products, and pulp and paper industries, along with the Canadian Wood Fibre Centre of Natural Resources Canada (NRCan). It drafted CLT plant qualification and product standards and passed them to the American National Standards Institute (ANSI)accredited APA–Engineered Wood Association committee to be used as ‘seed documents’ for the development of a single North American product standard. This would then be the

CONSTRUCTION CANADA WOOD DESIGN

The panels can also be used in combination with post-and-beam wood frame or steel frame componentsâ&#x20AC;&#x201D;the vertically oriented panels enclose the building similar to tilt-up construction. Photo courtesy KLH

Horizontally oriented panels span across beams to create the floor plates. Images courtesy FPInnovations

basis for an International Organization for Standardization (ISO) standard that would harmonize North America with Europe. (An ISO task group was formed under the ISO Technical Committee on Timber Structures for this purpose.) It is anticipated manufacturers will use the proposed standards to gain acceptance of proprietary CLT products by code-recognized evaluation services such as Canadian Construction Materials Centre (CCMC) and the International Code Council Evaluation Service (ICC-ES). A North American advisory committee on CLT has also been formed to advance the implementation of cross-laminated timber technology. In turn, this group formed a research/standards subcommittee so the related activities could be streamlined. Based

CONSTRUCTION CANADA WOOD DESIGN

Opening in a CLT floor for mechanics.

on the initial assessment, seismic and fire design issues have been identified as the most important ones to address. The American Wood Council (AWC) and Canadian Wood Council (CWC) have already initiated the process of implementing CLT in the material codes. These forthcoming documents should deal with: • grade of softwood to be used; • certain lay-up requirements; • quality control during fabrication; • structural design standards; and • plant quality standards. Each manufacturer will be required to meet minimum standards, but the companies will be allowed to develop their own systems, much like in Europe. Some manufacturers may choose to use other wood products such as laminated veneer lumber (LVL) or oriented strandboard (OSL) in their panels; others may follow some of the European systems and employ internal wood dowels, keyways, grooves, spaces between laminates, or varying laminate orientation.

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This five-storey residential complex in Berlin, Germany, benefits from CLT use.

Regardless of the provider, the end-products share certain characteristics. They are all prefabricated and manufactured in a controlled environment and processed using automation and CNC equipment. Further, all CLT products are easily assembled on construction sites, and can be used as monolithic walls, floors, ceiling, elevator shafts, and stairwells. Guidelines will be released for architectural detailing, engineering, and construction. Research is ongoing related to all the issues normally associated with any new product in the building code: • strength and seismic performance; • connections; • fire resistance; • thermal behaviour; • acoustic and vibration performance; and • durability. Much of this research has already been carried out in Europe and Canada.

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Located in Växjö, Sweden, the Limnologen Project is an eight-storey building made out of CLT.

Resource for further work While Canadian design/construction professionals await these new standards, a comprehensive overview of the use of cross-laminated timber has just been released by FPInnovations. Unveiled in early 2011 at a symposium sponsored by the Wood Enterprise Coalition of British Columbia, the CLT Handbook draws on European experience and FPInnovations’ multi-disciplinary research program that was launched under the auspices of NRCan’s Transformative Technologies Program in 2005. The peer-reviewed reference provides immediate support for the design and construction of CLT systems as alternative solutions in building codes, along with technical information related to: • manufacturing; • structural design; • seismic performance; • connections; • duration of load and creep;

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Another look at the construction of Limnologen.

• vibration performance; • fire performance; • acoustic performance; • building enclosure design; and • environmental performance. “The CLT Handbook will be instrumental in guiding building and design specialists as they seek use of this innovative new wood building material in non-traditional applications,” explained Mary Tracey, executive director of WoodWORKS! BC and executive member of the Wood Enterprise Coalition (WEC). “The possibilities are exciting, and we look forward to realizing the full potential of cross-laminated timber as a renewable alternative building material in Canada as we see construction of the first Canadian projects using CLT,” she said.

CONSTRUCTION CANADA WOOD DESIGN

CLT panels can be used in both horizontal and vertical applications.

Conclusion Major changes to the line of forest products do not happen very often. Further, experience over the last century or so has shown new products—such as OSB, I-joists and structural composite lumber (SCL)—take time to develop and to gain market acceptance. Manufacturers, trade associations, and researchers in Canada and the United States are working hard to provide support to designers and builders who want to use CLT products in their projects in the near future. The forest products industry is actively conducting research and developing the materials, standards, and guidelines to bring cross-laminated timber panels to the North American market in a very short timeframe.

Notes 1

An earlier version of this article, “A New Generation of Solid Wood Panels,” appeared in the Fall 2010 edition of the Canada Wood Council (CWC) magazine, Wood Design and Building.

CONSTRUCTION CANADA WOOD DESIGN

Part Two Designing for Timber-framed Buildings

BY MATTHEW REID, MASC., P.ENG., AND CORY ZURELL, PHD, P.ENG.

Matthew Reid, MASc., P.Eng., is a project engineer at Read Jones Christoffersen Ltd. When he wrote this article, he was an associate with Blackwell in the Toronto head office. He had worked at the structural engineering firm for five years, completing mainly renovations and additions to institutional, commercial, and residential projects. Reid sits on the Canadian Standards Association (CSA) Technical Committee A307 on Solid and Engineered Wood Products, and completed his master’s thesis in 2004 on bolted connections in glued-laminated timber. Cory Zurell, PhD, P.Eng., is a senior associate with Blackwell’s Waterloo, Ont., office. He is also an adjunct assistant professor at the University of Waterloo School of Architecture and sits on the APA–Engineered Wood Association’s Standards Committee on Cross-laminated Timber Panels. Zurell has been involved in structural consulting and education for 14 years and has a particular affinity for timber structures. He can be reached at czurell@blackwell.ca.

CONSTRUCTION CANADA WOOD DESIGN

Photo © Ben Rahn. Photo courtesy A-Frame Studios

Timber-framed Buildings Various adaptive reuse considerations for fire, acoustics, and structure For more than a decade, urban renewal has seen the renovation of former manufacturing facilities into trendy loft-style offices, condominiums, and apartments. Most of these buildings belong to the ‘brick and timber beam’ vernacular constructed in the first half of the 20th century. Many constraints govern the design of any building, but a renovation involves the most significant—the building already exists.

CONSTRUCTION CANADA WOOD DESIGN

An industrial building has been sand-blasted for its conversion to loft-style office space. Photos © Cory Zurell

These brick-and-beam buildings vary widely in terms of construction quality, materials, past performance, and ongoing durability. With older buildings, one must be cautious of developers who have contracted ‘strong old building’ syndrome—just because the building is old does not justify the assumption it was well-built and will last forever. As a result, educating owners and architects sometimes becomes part of the structural scope of work. In repurposing former manufacturing facilities, the renovation usually involves a change in occupancy. In Ontario, such work falls under the Ontario Building Code’s (OBC’s) Part 10, Change of Use, and Part 11, Renovations. Adapting an historical structure for today’s needs, considering current building standards and architectural intent, involves several significant issues. Three particular ones—fire, sound, and structural capacity—are more sensitive in the reuse of buildings when the existing structure is timber, or when timber is the desired solution for an addition. Inter-related, these all directly impact the architectural design and performance of the renovation or addition.

Fire safety The Ontario Building Code requires evaluation of the building’s fire safety when a renovation occurs. An experienced code consultant is valuable for establishing the fire protection and occupancy safety requirements, even when a change of major occupancy does not occur. The code consultant writes a report outlining how the architect should

CONSTRUCTION CANADA WOOD DESIGN

Figure 1 Framing Assembly (assuming 1.9-kPa live-load allowance, no partitions)

STC

IIC

Fire Rating

Increase in Load

15.5-mm plywood on 2x10 joists

No rating

12-15 min

15.5-mm plywood, 2x10 joists, 89-mm insulation, 15.9-mm drywall

30-45 min

+5.6 per cent

15.5-mm plywood, 2x10 joists, 89-mm insulation, resilient channels, 15.9-mm drywall

30-45 min

+5.6 per cent

38-mm concrete, 15.5-mm plywood, 2x10 joists, 89-mm insulation, resilient channels, 2x15.9-mm drywall

60 min

+43 per cent

An example of light-frame wood floor assemblies, corresponding to sound transmission class (STC), impact insulation class (IIC), and fire ratings, and relative to impact on loading. Information based on the 2005 National Building Code of Canada (NBC)

apply OBC Part 3, Use and Occupancy, which relates to the fire protection and occupant safety of any extension made to the existing building, alongside the requirements of OBC Part 11, which outlines the requirements for the existing portion of the building. Part 11 uses the term “performance level” for structural evaluation, early warning/ evacuation system requirements, and fire protection to determine whether an upgrade is required. Employing a code consultant can produce significant returns in some cases. On a project worked on by one of the authors, the code consultant was able to navigate through the code requirements such that the change from industrial to residential occupancy produced a reduced hazard index (HI) and, thus, the work was regarded as a “minor renovation.” This result allowed a non-combustible partial fifth storey to be added to the four-storey timber-framed building. Without the “minor renovation” result of the code report, this addition would not have been possible. When there is a change of “major occupancy,” as defined by OBC Part 10, the building is required to be classified as to its construction type, which is called its construction

CONSTRUCTION CANADA WOOD DESIGN

This column had been offset to accommodate an industrial process in a former manufacturing facility. The current location is structurally inadequate; during the conversion to offices, the column will be relocated to its original position to reinstate the original load-path. Photos ÂŠ Cory Zurell

index (CI), and as to its occupancy type, which is called its hazard index. The CI is compared to the HI to determine if an upgrade to the building is necessary; if the HI is higher, an upgrade is required. The buildingâ&#x20AC;&#x2122;s construction index is given a number between one and eight, where one is the lowest fire protection performance level. The construction index has two parameters: fire-resistance rating (FRR) and type of construction. The type of construction is a choice between combustible and non-combustible. The hazard index, like the construction index, is measured on a scale of one to eight, and is designated as the life safety hazard to occupants. The hazard index is defined by the occupancy group and building size. For adaptive reuse, one commonly sees an occupancy Group F (low-hazard industrial, manufacturing) change to either Group A (assembly areas such as schools) or Group C (residential areas). As a combustible material, the current code limits timber with respect to its construction index. The highest level timber can receive is a CI of five. It does not matter if the building controls flame spread, as defined in Part 3 and not considered

CONSTRUCTION CANADA WOOD DESIGN

Light wood framing had been used to infill a floor opening in this former industrial building. During the conversion of the building to offices, it may have to be either replaced with heavy timber or covered with drywall to achieve the required fire rating. A code consultant can provide valuable guidance on such issues.

under Part 11. The common case is an historic manufacturing building of heavy timber with a CI of five, which requires an HI of six. Part 11 has compliance alternatives, so an alteration to the building can still occur. A common solution is to provide a sprinkler system. The construction index also does not consider the potential of a non-combustible assembly that includes combustible material. For example, a floor assembly of concrete topping on plywood and wood joists with two layers of fire-resistant gypsum board ceiling is considered combustible. However, an alternative solution could be submitted to demonstrate the floor assembly meets the objectives of the fire protection clauses. The 2005 National Building Code of Canada (NBC) has taken its first steps toward a truly objective framework by introducing objectives and function statements, thereby allowing alternative solution submissions. If one wants to preserve and expose historical elements during an adaptive reuse conversion, then designers must be more comfortable knowing how to formulate an alternative solution submission. As time progresses and the construction industry becomes used to objectives and function statements, alternative solution submissions will be completed quite easily, and become just one more step in the design process.

Sound transmission The material benefits of timber include a relatively high strength-to-weight ratio. This acts against performance in terms of sound transmission; the lack of mass hurts the structureâ&#x20AC;&#x2122;s ability to attenuate both ambient and impact sounds. In historic manufacturing facilities, sound transmission would rarely have rated consideration. In repurposing such a facility, upgrading sound transmission ratings between floors is frequently necessary when residential occupancy is considered, and usually affects the structure.

CONSTRUCTION CANADA WOOD DESIGN

A timber beam with steel channel reinforcing can be seen above. While load can be transferred into the channels through bearing of the purlins on top of the channels, that same load cannot be effectively transferred out of the channels to the column—the single bolt at the end is poorly located and completely insufficient for the load involved.

The NBC stipulates a sound transmission class (STC) rating of 50 between units for multi-family residential buildings (increasing to 55 at elevators). No impact insulation class (IIC) is specified, but good practice is a rating of 55 to 65.1 For other occupancies, there is no guidance provided in the code, but best practices are established. There are several possible methods to increase the STC and IIC ratings of an existing timber structure, including: • adding a concrete topping for additional mass, affecting structural capacity, including seismic performance; • installing a suspended gypsum board ceiling (again, for additional mass) to cover timber that may otherwise be exposed and esthetically appealing; and • providing a floating floor such as hardwood on a resilient underlay (a minimal effect structurally, though less effective in terms of attenuation than the other options). The sound performance ratings of various assemblies are provided in NBC. For example, ratings of select light-frame wood assemblies are given in Figure 1 (page 22) for comparison. Depending on the condition and capacity of an existing structure, a substantial increase in dead load may not be of tremendous concern. If the original load capacity was high, there will not be a problem. However, this is precisely the issue—old buildings do not necessarily have the capacity one would expect, regardless of the previous occupancy.

Structural capacity Under Part 11, OBC requires the completed building to maintain its level of structural performance. An existing performance level is considered to be reduced if the existing structural systems cannot adequately support the proposed loading that is caused by the renovation, and when:

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Any loads carried by the steel reinforcing channels are effectively transferred to the supporting column through direct bearing.

• there is a major occupancy change; • the occupant load has been increased by more than 15 per cent; or • the live load has been increased due to change in use within the same major occupancy group. Assessing the structural capacity of existing buildings is simple when the original structural design drawings exist. When it comes to pre-1950 buildings, this rarely happens with any type of construction, much less with the brick-and-beam type of buildings of the early 1900s. It is likely a structural engineer did not design the building in the first place and structural drawings may never have existed. With the original design intent and criteria lost to the ages, and complicated by varying quality of regulation at the time of construction and inconsistent structures, assessing the capacity and adequacy of the structure falls to the design team to complete the renovation. While in some respects it is reasonable to assume a building has stood the ‘test of time,’ one cannot assume all inadequacies will have revealed themselves over the years. While the building may have performed satisfactorily in its previous life, even if the change in occupancy brings a theoretical loading reduction, there is no guarantee the building will be suitable for its repurposed life. Repurposing can involve various changes, but with respect to the timber structure, one can generally break down the work into two broad categories: minor changes and repairs, and major renovation and remediation. Minor changes may involve alterations for new mechanical equipment and services as well as a change in occupancy, but not significant changes in the loading of the building. In general, this would require the engineer to get a feel for the structure’s capacity. Timber varies in grade and species, but some basic reasonable assumptions, based on the building’s approximate age, can expedite the process and preclude a full and costly grading assessment of the timbers.

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Existing heavy timber truss with exposed wood decking and dimensional lumber rafters. Photos ÂŠ Matthew Reid

For light framing (usually full-dimension, rough sawn lumber), one can typically assume Spruce-Pine-fir #2/Northern Select Structural when assessing minor changes. (These two species gradings are conveniently close in strength and past gradings have rarely been found to deviate.)2 For heavy timber construction, historic buildings are generally found to fall into two possible scenarios as far as grading is concerned. For structures in the range of less than 80 to 100 years old, one generally finds timbers to be Douglas fir, grading to No. 1 or better. Older timber structures (and particularly those built before the completion of the Canadian Pacific Railway [CPR]) tend to be of Northern speciesâ&#x20AC;&#x201D;Select Structural being common. However, these assumptions are just a starting point, and though such findings are very common, one can just as easily encounter timber framing that includes, for instance, maple and elm in the mix.

CONSTRUCTION CANADA WOOD DESIGN

To convert an existing attic into university studio classrooms, skylights were used to add more light. The existing dimensional lumber roof rafters were modified with engineered lumber to accommodate the opening. All dimensional lumber required a fire rating, with the existing heavy timber allowed to be exposed provided the space was sprinklered.

The existing one-storey heavy timber trusses were modified with cranked steel beams to open the space. The non-combustible steel was allowed to be unrated, but the dimensional lumber required drywall in order to achieve a 45-minute fire rating. As shown on the right, new steel columns and beams were used to modify an existing heavy timber truss.

Major renovations, residential conversions in particular, frequently include the addition of a concrete topping to deal with sound and other performance issues. In this case, if assumptions do not provide an obvious and favourable resultâ&#x20AC;&#x201D;such as a load capacity well in excess of what is required by current codesâ&#x20AC;&#x201D;a full grading assessment of the timbers, complete with sampling for determination of species, may well be required. In-situ grading of timbers is a specialized skill. Licensed timber-graders employed at a sawmill will not grade timber beams and columns in an existing building. Since all four sides of beams are rarely exposed to view, a complete grading cannot be performed. This is where engineering experience and judgement combine with grading skills to assess the in-situ condition.3

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An existing church cathedral space was adapted to be residential lofts, where the authors were part of a team that added two floor levels within the cathedral space.

In addition to generally accepted engineering principles and conventions, building codes provide additional guidance for assessing existing structures. NBC includes Commentary L, “Application of NBC Part 4 of Division B for the Structural Evaluation and Upgrading of Existing Buildings.” This commentary principally addresses criteria for the ultimate limit state (ULS) affecting life safety. Commentary L includes a method of evaluation based on past performance (for all loadings except for seismic) and provisions for reduced load factors based on risk category and a calculated reliability level. Reduced load factors are used as a measure of the performance of the existing structure against new loading requirements. If upgrades are necessary, the intention is one would then revert to the full requirements of Part 4, Structural Design, for any upgrade. When an upgrade is required, there is no significant potential for savings to use reduced factors as most of the cost will be labour, not materials. An interesting creative aspect to structural engineering is upgrading a building’s structural capacity. There are three basic options: simply replace the member, reinforce the member, or unload the member. Replacing the member seems simple on the drawings, but the design team needs to consider the feasibility of construction. Requirements for shoring and the accessibility of cranes or lifts need to be carefully considered. Likewise, reinforcing a member can be quite simple or complicated, depending on the context. Considerations include how the load is transferred into the new reinforcing, how the load then gets transferred back out of the reinforcing and into the building structure, and potentially jacking of the existing structure or pre-loading of the reinforcing to balance the load distribution.

CONSTRUCTION CANADA WOOD DESIGN

During an adaptive reuse project, cranked steel beams are handy to match the existing geometry of the existing building.

Unloading a member is certainly easier said than done. Shortening the span of a beam (adding a column for instance) will usually have significant implications—particularly from an architectural standpoint.

The bottom line The costs on any building project are always closely scrutinized. Of course, owners and developers like fixed fees, especially when it comes to paying for consultants. For most consultants—architectural, mechanical, electrical, civil, landscape—involved with repurposing an historic building, a fixed fee is relatively easy to determine. For instance, renovations usually involve completely new mechanical and electrical systems, so from that perspective it is comparable to new construction. A fixed fee for structural engineering services related to the assessment and renovation of an historic building is tremendously difficult to determine because a complete scope is nearly impossible to determine before performing the work—old buildings tend to be full of surprises. Who could predict a four-storey, four-wythe brick bearing wall would just be sitting on a slab-on-grade and have no foundation wall or footing? In the authors’ experience, fees from past projects have ranged from as low as a couple of thousand dollars up to many tens of thousands—and the fees do not necessarily directly relate to the building size. From a structural engineer’s perspective, the best practice is to proceed on an hourly basis until the faults of the building are known, and then attempt to carefully define the scope and corresponding fees.

CONSTRUCTION CANADA WOOD DESIGN

To convert an existing church into multi-family residential units, the authors needed to add the new floors on their own new footings, with new steel beams and new floor joists. From a fire safety perspective, the exposed heavy timber trusses are only allowed to support a roof; any type of floor including a mezzanine would require the existing timbers to be covered up with fire-proofing (such as drywall).

Adaptive reuse of historical buildings is not the cheapest form of construction and better returns on investment (ROIs) can likely be found elsewhere. However, cheap construction costs are not the driving force behind adaptive reuse. From heritage conservation of prime locations to recycling buildings and creating unique and uniquely marketable spaces, such endeavours can be profitable. Historic timber buildings are worth preserving. They just sometimes require a little work, particularly when sound and fire and the effects on structure are concerned.

Notes 1

See “Wood Frame Construction, Fire Resistance, and Sound Transmission,” by Forintek Canada Corp, Societe d’habitation du Québec and Canada Mortgage and Housing Corporation, 2002. 2 The noted assumptions for species and grade are particular for Southern Ontario, but similar trends can no doubt be determined for other regions based on common historic building practice. 3 The Ontario Forest Industries Association (OFIA) offers timber-grading courses.

CONSTRUCTION CANADA WOOD DESIGN

Part Three Trees in the Tower

BY JIM TAGGART, FRAIC

Jim Taggart, FRAIC, teaches history and theory in the architectural science degree program at the British Columbia Institute of Technology (BCIT). Taggart worked for more than a decade in the design and construction industry and has been focused on public and professional education since 1992. In 2001, he was inducted as a Fellow into the Royal Architectural Institute of Canada (RAIC). The author or editor of more than a dozen books, including the award-winning Toward a Culture of Wood Architecture (2011), Taggart was the 2012 recipient of the BC Premier’s ‘Wood Champion’ award. He can be reached at architext@telus.net.

CONSTRUCTION CANADA WOOD DESIGN

Photos ÂŠ Ed White Photographics. Photos courtesy CEI Architecture and Parkin Architects

Trees in the

Tower Designing the Surrey Memorial Hospital Critical Care Tower

The Surrey Memorial Hospital Critical Care Tower represents the most significant application to date of structural and non-structural wood products in a B.C. healthcare facility. The use of wood in publicly funded buildings is encouraged by the provinceâ&#x20AC;&#x2122;s Wood First Act, but it is also supported by scientific research linking exposure to daylight and views of nature with improved patient recovery times and occupant well-being.1

CONSTRUCTION CANADA WOOD

Designed by CEI Architecture and Parkin Architects, the Surrey Memorial Hospital Critical Care Tower makes significant use of structural and non-structural wood products in its lobby.

Healthcare architects worldwide have begun to introduce natural materials and forms into their work. One example is Surrey Memorial Hospital, which serves the diverse ethnic communities making up one of Canada’s fastest-growing cities. With an area of 39,250 m2 (420,000 sf), the Critical Care Tower is the largest healthcare project in B.C. history. This expansion to the existing hospital provides the community with worldclass family-centred care. The project adds new acute care beds, the largest emergency department in Canada, an adult intensive care unit (ICU), a neonatal centre of excellence, more space for the University of British Columbia (UBC) School of Medicine, and a laboratory with the latest medical technology.

Design approach The Critical Care Tower was conceived as the new front door to the hospital campus. The massing of the building is strong and simple, combining four durable natural materials—wood, glass, ceramic, and stone. The two-storey base of the tower is clad in a wood composite panel system that embraces the emergency department and neo-natal intensive care unit. The panelling is continued into the interior of the atrium. Rising above the wood base, the six-storey in-patient tower’s façade is glass embossed with a ceramic frit pattern. The glass inpatient tower is connected to the stone-clad circulation tower which is articulated as a separate element.

CONSTRUCTION CANADA WOOD DESIGN

The interior glued-laminated timber (glulam) tree structures, represent one of the hallmarks of this project. Photo © Jerald Walliser. Photo courtesy Fraser Health

These materials are united in a transparent entry pavilion, the roof of which is supported by two massive glued-laminated timber (glulam) ‘tree’ columns. The warm influence of wood extends from the main entry through the public areas to all the hospital floors, creating a welcoming atmosphere much different from that of a traditional institutional building.

Program innovation Patient and family care are at the core of the design, with all patient rooms having access to natural light and dedicated family space. Infection control, universal design, and disaster preparedness were also key priorities for the project. Extensive user consultation, evidence-based design, and ‘Lean’ principles were implemented to support clinical staff in providing the highest possible level of care.2 For example, the emergency department is designed in pods—self-sufficient zones that have centralized access to supplies and services. This enables isolation of areas in the event of a communicable disease outbreak or acts of violence. Similarly, in-patient areas provide clearly delineated on-stage and off-stage spaces with patient and visitor areas separated from core staff areas. Universal design (including ‘same-handedness’) supports staff familiarity and efficiency as they move between floors. Lean principles are also applied to reduce walking distances for clinical staff and strategically locate frequently used service rooms.

CONSTRUCTION CANADA WOOD DESIGN

The massing of the building is strong and simple, combining four durable natural materials— wood, glass, ceramic, and stone. Photos © Ed White Photographics. Photos courtesy CEI Architecture and Parkin Architects

Sustainable design The fast-track, design-build nature of this public-private partnership (P3) project demanded it be conceived and realized through an integrated design process. The owner, Fraser Health Authority, required the project achieve Gold under the Canada Green Building Council (CaGBC) Leadership in Energy and Environmental Design (LEED) program—an exacting standard for a building of this scale and complexity. Accordingly, the design team established performance goals within the context of the 30-year operating model used for the project. Design simulations predict a 47 per cent reduction in energy consumption when compared to the reference building under the Model National Energy Code for Buildings (MNECB). The new high-efficiency mechanical systems are integrated with the existing boilers, maximizing energy savings from the outset, while accommodating potential future upgrades or replacement of the existing plant. A flat-plate structure with minimal load-bearing walls and bracing ensures flexibility in the floor plans and supports future renovations and reconfigurations. It also maximizes the use of natural daylighting for energy efficiency and occupant well-being. Materials used in interior spaces contain either reduced levels of volatile organic compounds (VOCs) or no VOCs at all. Approximately 20 per cent of the materials used were extracted and manufactured within an 800-km (500-mi) radius. Wood was specified where possible for both interior and exterior applications—not simply

CONSTRUCTION CANADA WOOD DESIGN

Wood and Human Health Just as the definition of ‘green building’ has expanded with time, so too has the understanding of human health expanded to include not only physical condition, but also psychological well-being. Intuitively, people have known for a long time about humans’ affinity for nature, and that being in a natural environment can make people feel more relaxed. Scientists have now confirmed this sensation of relaxation in the presence of nature is the result of a physiological change—a reduction in the level of stress-related hormones produced by the body’s sympathetic nervous system (SNS). Researchers at the University of British Columbia (UBC) have determined the presence of wood in the visual environment produces the same effect.* With respect to physical health, wood contributes to humidity control by absorbing moisture from the air when the relative humidity (RH) is high and releasing it when the humidity level is low. Wood products and finishes also do not contribute airborne contaminants since they are dust-free after installation and easily maintained. Further, properly selected adhesives and coatings, will emit few, if any, harmful vapours. * For more, see D. Fell’s 2002 report for FPInnovations, “Consumer Visual Evaluation of Canadian Wood Species” at forresweb.com/fpi-publications. Its conclusion discusses how the presence of wood in the visual field reduces the production of the stress hormone SNS, when compared to environments in which there is no visible wood. The results came from identical tests given to statistically similar groups of students conducted in environments with and without wood. This is very similar to the results achieved with evidence-based design, where stress levels are lower, and recovery rates quicker for patients who have a view of nature, compared to those who do not.

for its physical and psychological benefits, but also because it is a renewable and sustainable regional material. This growing recognition is based on third-party certification of sustainable forest management under one of three programs operating in Canada: Forest Stewardship Council (FSC), Canadian Standards Association (CSA), and Sustainable Forest Initiative (SFI). The country has approximately half of the world’s certified forest area, giving architects and specifiers assurance their use of wood should not be detrimental to the environment. Additionally, wood has a low (and sometimes even negative) carbon footprint because of the carbon dioxide sequestered as trees grow and because of the relatively small amount of energy used in harvesting and processing wood products. The sequesterd carbon remains within the wood throughout its service life as a structural or finish product, and the conversion of trees to durable wood components creates space in the forest for new trees that will continue the carbon sequestration process. Rather than having a detrimental impact on the environment, the by-products of wood processing can be turned into bio-fuel, which provides a carbon neutral energy source. In much of Canada, wood can be considered a local or regional material.

Wood use and the Wood First Act The government of British Columbia introduced the Wood First Act in 2009, as part of its comprehensive Climate Action Plan. Recognizing the low embodied energy, carbon storage capacity, and other environmental benefits of wood, the act requires the material be considered for structural and non-structural applications in publicly funded buildings, where functionally appropriate and permitted by code.3

CONSTRUCTION CANADA WOOD DESIGN

The expansion to Surrey Memorial adds new acute care beds, the largest emergency department in Canada, an adult intensive care unit (ICU), a neonatal centre of excellence, and laboratories.

It is also worth noting reclamation and recycling of wood can generally be accomplished with little or no reduction in its structural value. Further, as a finish, reclaimed wood is often preferred to new material. Thus, the Wood First Act was introduced primarily for new buildings, but its impacts will likely last beyond the initial service life of first generation structures. Wood is concentrated in the areas of public interface, including the exterior covered walkways, drop-off area, west entrance, and the link connecting the new tower to the existing hospital. This reinforces the connection to nature, potentially helping reduce patient and visitor stress and anxiety. The lobby, where families and loved ones will spend significant amounts of time, features an exposed wood structure, panelling, and millwork. Wood is also incorporated in interior ceiling panels, acoustic wall panels, built-in cabinetry, and the front of reception desks throughout the building, where it can be properly protected (i.e. from physical damage by gurneys, floor polishers and other equipment) and maintained. In some instances, laminate has been used in place of real wood veneer on solid-core wood doors where durability and the integrity of the finish are paramount.

Building code considerations Non-combustible construction is required by the B.C. Building Code (BCBC) for institutional occupancies of this size and height. Thus, the main body of the Critical Care Tower is a 10-storey reinforced concrete frame structure with interstitial service

CONSTRUCTION CANADA WOOD DESIGN

floors. The use of structural wood is predicated on the creation of a fire separation between combustible and non-combustible portions of the building that enables them to be considered as separate structures. As the entrance lobby is only two storeys, and does not contain any patient rooms, the code permits heavy timber to be used on an alternative solution basis for the roof and its supporting structure. This interpretation was possible because of the sloping grade along the west elevation. The heavy timber structure was permitted at the south of the building where only the second and third storeys are technically above grade. The code analysis identified the following requirements: • two-hour fire separation between heavy timber construction and the remaining B2 occupancy; • fire retardant treatment for all combustible construction; • principal firefighting entrances located at grade (second level); and • structure protected by sprinkler system.

Structural design of wood components With its heavy timber structure, the two-storey lobby sits adjacent to the base of the main tower and is structurally distinct from it. The heavy timber roof structure consists of an upper layer of glulam purlins supported on a lower level of glulam beams. Both layers of this structural lattice cantilever 6 m (20 ft) beyond the line of the exterior curtain wall. The roof deck is profiled metal, exposed on the underside. This structural lattice is supported on two massive glulam tree columns, each consisting of four composite glulam and steel curved elements, closely spaced at the base and spreading out like branches as they rise through the lobby. Each element consists of a pair of glulam beams, anchored to a steel base plate, and held apart at intervals throughout their height by 100-mm (4-in.) steel spacers. The curvature of the beams and the cantilevering roof were the determining factors in the sizing of members and the design of connections. The four curved elements are connected at two points by horizontal steel rings and again at the top by diagonal steel tension rods. This arrangement stabilizes the tree structure, resisting the natural tendency of its individual elements to buckle or spread apart. The potential for large deflections to occur in the cantilevered portions of the roof informed the design of the connections between the roof beams and the top of the exterior curtain wall. The weight of the curtain wall is borne by the steel plate mullions, so the roof is required only to resist the lateral loads. A plate connection with a slotted hole was used to ensure no vertical roof loads would be transferred to the steel plate mullions. “With wood structures, it is always the connections that drive the design and often this can lead to interesting and unique solutions,” explained Clint Low, of the structural engineering firm for the project, Bush, Bohlman & Partners. Although the exterior canopy was more straightforward to design, it still posed certain challenges. The roof of the canopy is at a consistent height along the length of the west wall, but the section in front of the atrium is a taller structure, on account of a 1.5-m (5-ft) change in grade. The height and location of the taller canopy added complexity to the lateral design. In the longitudinal direction, it is tied into the upper level canopy where the seismic loads are dragged into the building by drag rods. Since it could not be tied back to the curtain

CONSTRUCTION CANADA WOOD DESIGN

Wood is incorporated throughout the Surrey project in an attempt to reap the rewards of both its esthetic and functional benefits.

Project Team Owner: Fraser Health Authority Construction Manager: EllisDon Architects: CEI Architecture and Parkin Architects Structural: Bush, Bohlman & Partners Mechanical/Electrical/Civil Engineering and Traffic Planning: MMM Group Acoustic and Noise Control: Daniel Lyzun Code: CFT Engineering Geotechnical: Levelton Landscape: Phillips Farevaag Smallenberg

wall, the higher cantilevered canopy is made stable in the other direction through the use of vertical tie rods that connect the beams to concrete pilasters at each bay.

Installation challenges Awarded the subcontract for fabrication of the heavy timber elements, StructureCraft Builders took the design by Bush, Bohlman & Partners and made refinements to improve efficiency, economy, and constructability. On the low and high canopies, which included numerous glulam purlins, StructureCraft chose not to install these piece by piece, but rather to prefabricate the 2.8-m2 (30-sf) elements onsite, then lift them into place as a single unit. The original design for the curved columns of the canopy included a continuous steel knife plate sandwiched between paired glulam elements. To simplify fabrication and reduce the overall cost, StructureCraft suggested increasing the size of the glulam elements and eliminating the knife plate, while maintaining the required shadow gap using plywood spacers. Similarly, a steel hollow structural section (HSS) spacer between the vertical glulam elements was eliminated by redesigning the column-tobeam connections as a moment frame.

CONSTRUCTION CANADA WOOD DESIGN

The curved pieces in the tower’s center—designed to evoke DNA strands—were constructed from cedar glulam material. The typical connection employs a through-bolted knife plate and a screwed back plate. Epoxy is injected to fill the space around the knife plate.

For the large tree columns, the primary concern was constructability. Although the four-column tree configuration, tied together by steel rings and connected to the glulam lattice roof, was designed to be stable in its final configuration, finding a way to have it erected safely, piece-by-piece, was a considerable challenge. The chosen solution was to use adjustable tilt-up shoring to stabilize each prefabricated paired column unit as it was manoeuvered into place. Secured to its base plate, and with shores essentially creating a temporary tripod structure, it was possible to erect all four columns independently and then to install the ring connectors.

Conclusion This project provides further evidence Canada’s healthcare sector now recognizes the important role that can be played by wood in the creation of healing environments. 4 Beyond the environmental advantages it offers, the physical and psychological benefits of wood make it a desirable choice not only in healthcare facilities, but also in buildings of all sizes and types. As a new generation of architects and engineers rediscover the potential of the material, one can expect wood to play an ever more prominent role in the country’s public buildings.

Notes 1 A paper summarizing related research can be found at https://smartech.gatech.edu/ jspui/bitstream/1853/25676/1/zimring_HERD_2008_researchlitreview.pdf. 2 ‘Lean’ refers to a planning and design methodology that aims to identify and enhance practices that are effective and efficient, while eliminating those that are not. 3 In British Columbia, combustible construction is permitted by the code for certain sizes, heights, and occupancy classifications, but not always used. The Wood First Act aims to promote the greater use of wood inthese applications. 4 For more, visit www.wood-works.ca/bc/case-studies-videos.”

CONSTRUCTION CANADA WOOD DESIGN

Part Four Specifying Modern Timber Connections

BY MAIK GEHLOFF, DIPL.-ING. (FH), M.A.SC.

Maik Gehloff, Dipl.-Ing. (FH), M.A.Sc., is the founder and owner of Gehloff Consulting Inc., providing services including technical support for timber connections for many years. Gehloff holds a degree in wood science and technology, specializing in timber engineering from the University for Applied Sciences in Eberswalde, Germany, as well as a degree in timber engineering from University of British Columbia (UBC) in Vancouver. His research projects focused on self-tapping, structural wood screws, as well as other modern wood connectors. Gehloff is a member of the Timber Framers Guild of North America and the Timber Frame Engineering Council. He can be reached at mgehloff@gehloff-consulting.com.

CONSTRUCTION CANADA WOOD DESIGN

Photo courtesy Tanya Luthi, Fast + Epp

Specifying Modern

Timber Connections Widely used in conventional frame construction, wood is not new to the Canadian design community. What is â&#x20AC;&#x2DC;new,â&#x20AC;&#x2122; however, are changes to building codes that allow for taller structures to be constructed of wood, along with the introduction and development of new products like cross-laminated timber (CLT) and other massive wood panels manufactured from laminated veneer lumber (LVL) or laminated strand lumber (LSL).

CONSTRUCTION CANADA WOOD DESIGN

The Philip J. Currie Dinosaur Museum project in Wembley, Alberta, was designed by Teeple Architects. It makes use of the latest in wood connection technology for its innovative form. Photos courtesy Fast + Epp

The prospects could get even more exciting with composite materials, such as woodconcrete composites or the clever combination of wood and steel. An abundance of recent innovative buildings have been built using these newer products based on the time-tested material.1 In creating these impressive structures, various factors had to be considered and solved both in understanding the material with its beneficial and challenging properties. Wood not only provides a warm esthetic, but it is also strong, easily workable, and sustainable. It is a renewable resource, and it can significantly reduce a building’s carbon footprint. On the other hand, wood is a hygroscopic, non-homogeneous, and un-isotropic material with inherent weaknesses like its low compression and tension perpendicular to the grain strength and its low capacity in longitudinal shear. All these challenges, however, can be overcome by: • creating more stable products (such as CLT); • employing it in composites in order to effectively use the best properties of the comprising materials; • reinforcements; and • proper detailing.

CONSTRUCTION CANADA WOOD DESIGN

The museum features a locally sourced timber structure and perforated acoustic wood finishes.

Quite likely, the most challenging endeavour is the connections in these wood or timber structures. Most building structures can be thought of as collections of beam and plate-like elements held together by connections. In wood and timber projects, however, the opposite is true: they can be viewed as collections of connections held together by beam and plate-like elements. A lot of energy has been spent on the constant improvement of glued-laminated timber (glulam), CLT, and other engineered wood products like LVL, LSL, and parallel strand lumber (PSL). In Canada and the United States, however, the development of connections has not kept up with these changes. North American material codes still look at nails, timber rivets, screws, lag-screws, bolts, and threaded rods, as well as shear-plates and split rings. All these connectors still have their place in timber engineering and construction, but to really push the envelope for wood buildings like the currently under-construction Wood Innovation and Design Centre (WIDC) in Prince George, B.C.,2 new and innovative connectors and connection systems have to be explored and used.

STS 101 One of the most prevalent innovations in timber engineering was the development of engineered self-tapping wood screws (STS).3 These screws are a far cry from the decking screws and the conventional wood screws to which many are accustomed.

CONSTRUCTION CANADA WOOD DESIGN

An understanding of not only engineered wood capabilities, but also fastener attributes, is critical for timber construction.

Modern STS do not require pre-drilling or pilot holes; they work well in most materials and are designed to ‘cut’ or form threads into the material as they are driven in. Some STS tips look similar to a drill bit, but they lack flutes—in other words, they do not remove material from the hole. Instead, the tips slightly loosen the material to reduce friction and drive-in torque, which is especially beneficial for the fully threaded varieties of self-tapping wood screws. Self-tapping wood screws come in countless different diameters, lengths, and headtypes, along with fully threaded or partially threaded versions. Some of the main characteristics of STS are their generally smaller core diameter with larger thread wings, leading to less splitting and more bite (and therefore high withdrawal capacity). The high capacity in withdrawal is also achieved through the high tensile capacity of the screw’s steel due to hardening and quenching process of the screws during the manufacturing. The partially threaded version of the screws also feature an improved shank cutter that further reduces the friction during installation of the screw, lowers the risk of clogging of the shank cutters, and creates a hole larger than the core diameter of the screw to allow for shrinkage and swelling of the wood without getting hung up on the screw’s shaft. All these characteristics combined create an efficient and economical connector in timber connections that is easy to apply, without the need of pre-drilling and has a high withdrawal and tensile strength. Their availability in Canada is generally not a problem.

CONSTRUCTION CANADA WOOD DESIGN

Self-tapping wood screws being installed during the construction of the Wood Innovation and Design Centre in Prince George, B.C. Photo courtesy www.naturallywood.com

Understanding self-tapping screws and timber construction When looking at the possible STS applications, it becomes clear why they helped revolutionize the field of timber engineering and construction. Self-tapping wood screws can be used by themselves as primary fasteners or reinforcement, or in combination with other parts (e.g. steel plates and weldments or standardized connectors). The principle on which they work remains their incredible capacity in withdrawal. An example for the use of these screws as a primary fastener could be a common wood-wood (-wood) / steel-wood (-steel) / wood-steel (-wood) connection with one shear plane or two shear planes respectively. That type of connection is usually achieved by bolting the individual members together and transferring the forces through shear in the bolts. The same connection could also be done using STS by installing the screws at a 45-degree angle, and then transferring the loads through the screwâ&#x20AC;&#x2122;s axis. A connection using screws would yield a higher capacity with fewer or smaller screws without the need of pre-drilling. In many cases, timber members have to be over-sized to allow for the end and edge distances required for a bolted connection. Due to the smaller diameters and reduced number of screws, the timber member in most cases would not need to be oversized anymore. This results in an added economic benefit. The same can be said for screws used as reinforcements. Instead of being over-sized due to notches or protrusions, beams can be reinforced with self-tapping screws; in

CONSTRUCTION CANADA WOOD DESIGN

Figure 1

This form-fitting connector is being installed on a glued-laminated timber (glulam) beam in the plant with self-tapping screws (STS) before being shipped to a construction site where the two parts simply slide together. Photo courtesy Structurlam Products LP

most cases, they can be kept at the cross-section of a beam without such notches. For example, in the case of a notch or a bolted connection, wood would be loaded in tension perpendicular to the grain—one of wood’s inherent weaknesses. Concessions would have to be made to transfer that load over a larger area. When a self-tapping wood screw is used, the force transfers along the screw’s axis, again employing the high capacity in withdrawal—the beam or connection geometry does not need to be altered.

Specialized screws Some manufacturers have also created self-tapping wood screws with specific features tailored to specialized uses. For example, this author knows of two companies who produce screws with two different pitches, allowing them to draw a pair of members tightly together as long as the change of pitch is located right in the interface between the two members. One company has developed screws with a progressively changing pitch, allowing it to tightly draw together multiple members without the need to ensure a proper interface placement. Companies have also developed screws with an additional threaded part under the head. The thread under the head has the same pitch as the regular thread—this ensures a certain amount of spacing between two elements without compressing insulation, for example, in between. Instead of transferring the load from one element to the other relying on the material between them, the loads are transferred through the screw shaft.

CONSTRUCTION CANADA WOOD DESIGN

There is another product that technically is not a screw, but rather a tight-fitting dowel able to drill through the wood and up to three steel plates. It has a short-threaded part under the head to secure the dowel from falling out. Manufacturers have also engineered various methods for shear transfer between wood and concrete in wood-concrete composites. In some cases, the screw has a distance marker to ensure it is driven to the correct depth before the concrete is poured; in other examples, a placeholder is cast into the concrete allowing for precast elements. Onsite, screws are later installed through the placeholders, ensuring proper shear transfer between the concrete and wood. There is even a screw that has threads for both concrete and wood. When installing sill plates, a hole can be drilled through the wood into the concrete, and then the screw driven to connect the two. The benefit is the perfect alignment of the hole in wood and concrete as they are drilled in-situ at the same time. When it comes to the length of self-tapping wood screws, some manufacturers offer 1-m (3.3-ft) and 1.4-m (4.6-ft) models. These long screws can be used in part as replacements for glued in threaded rods in moment connections, but it is recommended a small pilot hole be pre-drilled in order to set the installation angle and to reduce the friction and drive-in torque. Timber moment connections can also be achieved using common connectors augmented with the STS as reinforcements to increase capacity. There are also steel plates that, together with their screws, can be used in a system to create a timber moment connection.

Further developments in STS When it comes to using self-tapping wood screws with other systems, the sky seems to be the limit, reaching from simple steel plates, custom weldments of any shape imaginable, or standardized system connectors. The principle, however, remains the same by using the STS in withdrawal by â&#x20AC;&#x2DC;hangingâ&#x20AC;&#x2122; these system connectors off or on them. Figure 1 shows a proprietary product, a form-fitting connector employing the time-honoured shape of a classic dove-tail, being installed on a glulam beam in the plant with STS, before being shipped to the Prince George site of the WIDC where the two parts simply slide together. The advantage of the various proprietary connection systems lies in the fact they are standardized, allowing designers to simply pick from a catalogue based on the required capacities, minimizing time for design and drafting, for example, custom steel weldments. Additional benefits of standardized systems are higher quality control and reduced assembly times due to a higher grade of pre-manufacturing, as their individual parts are shop-installed. Some of these standardized connection systems provide capacities up to 600 kN (134,885 lb), and simple steel plate tension splices in excess of 1 MN have been achieved solely by virtue of self-tapping wood screws (granted, a lot of them). While STS development keeps progressing and more new ways of using them are being explored, another modern connection system is holding entry into the North American market: epoxy. The principle itself is not new, but there is innovation in using an existing and developing technology in timber engineering and engineered timber construction.

CONSTRUCTION CANADA WOOD DESIGN

Figure 2

= withdrawal capacity of the screw

= tensile capacity of the screw = characteristic (5th percentile) timber density [kg/m3], to be taken as the lesser of the mean density * 0.84 and the 5th percentile density = reference density [kg/m3], from manufacturer’s ETA = characteristic (5th percentile) withdrawal parameter [N/mm2], from manufacturer’s ETA = characteristic (5th percentile) head pull-through parameter [N/mm2], from manufacturer’s ETA = characteristic (5th percentile) tensile strength of the screw [kN], from manufacturer’s ETA = nominal screw outside diameter, as per manufacturer’s ETA = effective embedment depth [mm] = angle between screw length axis and wood grain [°] = effective number of screws The screw’s characteristic or specified (unfactored) capacity in withdrawal is to be taken as the minimum of the values calculated above.

The EuroCode 5 (EC5) equation.

Two technologies in particular have successfully been used in North America. One system is a wood-concrete composite using a glued-in steel mesh as shear connector between the wood and the concrete, whereas the other is a steel mesh welded to a steel connection plate and then the mesh glued in the wood for a steel-wood composite that can now be joined to other materials. The great advantage of these systems is their high strength and stiffness while still being ductile. The system can be used to create strong and stiff moment connections, and has been used in the feature staircase of University of British Columbia’s (UBC) Earth Sciences Building (ESB) in Vancouver. When it comes to the design and engineering of connections using self-tapping wood screws or standardized connection systems, only one manufacturer currently has a Canadian Construction Materials Centre (CCMC) report to use alongside Canadian Standards Association (CSA) O86, Engineering Design in Wood. However, this does not mean the screws of other manufacturers cannot be used. The CSA standard has a provision in 3.3.2 for new or special systems of design and construction. Based on this, such systems can be used without a CCMC report if they are following engineering principals and/or reliable test data. In the case of

CONSTRUCTION CANADA WOOD DESIGN

Concealed modern wood connection after installation at the Earth Sciences Building (ESB) located on the University of British Columbia (UBC) campus in Vancouver.

STS and any of the other standardized systems, the engineering can be done following some adopted provisions of the EuroCode 5 (EC5) and the manufacturerâ&#x20AC;&#x2122;s European Technical Approvals (ETA). To gain ETAs, the manufacturers must go through a battery of tests fulfilling the CSA O86 provisions for reliable test data and applied EC5 and the ETAs to show the design follows engineering principles. The design process itself is not difficult; most distributers offer design tables to further simplify the process. Still, caution should be taken regarding the constraints of these design tables like densities and load duration factorsâ&#x20AC;&#x201D;such constraints are usually explained in the footnotes.

Engineering equations The following describes the design based on equations that would allow the engineer to be free of constraints and set all parameters as required for the project at hand. For STS loaded in shear, perpendicular to the length axis, it can be done with the yield equations given in CSA O86. For screws loaded in withdrawal, parallel to the axis of the screw, the main direction of loading in most cases uses the EC5 equation in Figure 2. When using this EC5 equation, special consideration has to be given to the characteristic (5th percentile) density. The densities for local wood species are given in CSA O86 as relative specific gravity (G) at a wood moisture content (MOC) of oven-dry.

CONSTRUCTION CANADA WOOD DESIGN

However, the densities used in EC5 are given as 5th percentile values at an MOC of 12 per cent. To use the CSA densities, some statistical ‘soft’ conversions implying certain assumptions have to be done. The conversion of relative gravity (a value relative to water with 1000 kg/m3 density) to density is straightforward, and the value can simply be multiplied by 1000. To convert the mean value to a 5th percentile value, the former is multiplied by 0.84, as shown in the equation. As a last step, the MOC has to be taken into consideration. The Wood Handbook by the Forest Products Laboratory of the U.S. Department of Agriculture (USDA) Forest Service gives great information of the effect of moisture content on the density and offers the following formula for conversion: ρk,0% = ρk,0% *(1+M/100) with M = 12% Putting it all together the following equation can be used to convert the CSA gravities (G) to EC5-compliant densities: ρk = ([G *1000] * 0.84)* (1+M/100) When it comes to establishing the factored design capacity, the provisions given in CSA O86 can be used or the EC5 provisions applied, since both codes are semi-probabilistic and use load resistance factor design with similar factors. The material safety factor for connections in EC5 (ϒM) is 1.3 whereas a common factor ϕ of 0.7 can be used for connections utilizing self-tapping wood screws. When looking at 1/ϒM = 0.769, it is slightly higher than the 0.7 used in CSA, but when looking at load duration factors and how they are established (which is beyond this article’s scope), the 1/ ϒM can be normalized to ϕ = 0.7 in combination with the use of the common Canadian load duration factors (KD). The engineering design of standardized connection systems from Europe using STS can be done the same way, but most manufacturer provide characteristic (5th percentile) values for their systems in their ETA as the number of screws per connector is fixed. In that case, only the safety factors have to be applied to the tabulated values. It is worth noting the tabulated values are, in almost all cases, tabulated solely for the reference density and the standard connection with screws at a set angle to the grain. With a system connector used in connections that are inclined or oblique, the designer has to calculate the capacity as the angle between screw axis and wood grain can differ from the standard situation and impact its capacity. This also means that competing connection systems have to be checked separately as comparison of the standard situation capacity difference between systems may not be linear; it could also be different for inclined or oblique connections. For example, if System A is 10 per cent stronger than System B in a standard situation, it may in fact prove to be weaker in other scenarios.

Conclusion Innovation almost always moves faster than building codes can react. Codes, however, give provisions for the use of emerging new systems and manufacturers do their due diligence in research and development.

CONSTRUCTION CANADA WOOD DESIGN

This bus shelter at the University of British Columbia was designed by Public: Architecture + Communication. Photo courtesy Tanya Luthi, Fast + Epp

All system types listed in this article, and more coming, are readily available in North America; in most cases, they are actually imported to the continent, but more specifically distributed from Canada. All these distributers offer technical support from within the country, and most also offer engineering support with knowledge of the prevailing codes. The respective technical support can be enlisted in helping with engineering design, ideas, and offer proper installation and application guidance and instructions.

Notes Numerous Construction Canada articles have focused on these innovative wood projects. Examples include “Why Wood Works: Designing the Richmond Olympic Oval,” by Jim Taggart (November 2009), “Building the Earth Sciences Building at the University of British Columbia,” by Eric Karsh (August 2013), and “Overcoming the Learning Curve: Design and Construction of the UBCO Fitness and Wellness Centre,” by Patrice R. Tardif (October 2013). Visit www.constructioncanada.net and select “Archives.” 2 For more on this project, see the article “Constructing an All-wood Building,” which was written by Werner Hofstätter, and appeared in the April 2014 issue of Construction Canada. 3 They should not be confused with self-drilling screws, which are connectors that physically remove material and are used predominantly in the metal industry—they do not work well in wood. 1

CONSTRUCTION CANADA WOOD DESIGN

Part Five Restoring Historical Architectural Woodwork in the Construction Industry

BY ALAN STACEY AND KATHY STACEY, B.SC.

Alan Stacey is a principal at Heritage Mill Historic Materials Conservation, and trained in both an indentured five-year apprenticeship as well as at Englandâ&#x20AC;&#x2122;s Salisbury College. He has worked in the conservation field in England, working with such collections as the 19th century ships models collections for the National Martine Museum in Greenwich and, in Canada, the Thompson Collection of 17th and 18th century ship models on permanent display at the Art Gallery of Ontario (AGO) in Toronto. Stacey is a member of ICOMOS Canada, Canadian Association of Conservators (CAC), and the Architectural Conservancy of Ontario. He can be contacted via e-mail at alanstacey@heritagemill.ca. Kathy Stacey, B.Sc., is a principal at Heritage Mill. Her past experience includes facilities management for the culture and recreation department as project coordinator, special projects, implementation of the Compulsory Competitive Tendering Act with regard to compliance, design and function of community cultural recreational buildings. Stacey lectures on the principles of building conservation to professionals with audiences from all government levels, the Construct Canada show, Heritage Canada Foundation, and the Educational Round Table for Education in the Heritage Field. She is a member of Project Management Institute (PMI), the Association for Preservation Technology, and the Architectural Conservancy of Ontario. Stacey can be reached at kstacey@heritagemill.ca.

CONSTRUCTION CANADA WOOD DESIGN

The Welland (Ont.) Courthouse, with work by VG Architects and Heritage Mill. All images courtesy Heritage Mill

Restoring Historical

Architectural Woodwork

in the Construction Industry There is a substantial number of heritage commercial and institutional buildings in Canada. Able to provide productive useful space for decades to come, these projects are culturally significant, serving to define the past and present, along with the cultural landscape in which we live and work. There was a time, not so long ago, when many owners and designers would choose demolition over adaptation and repurposing. Fortunately, many have gotten beyond this thinking and made progressive moves toward creatively adapting these historical structures.

CONSTRUCTION CANADA WOOD DESIGN

Successful historical architectural woodwork is both an art and a science. These three images demonstrate the need for the skills described in the article.

There are many excellent examples of these projects that span the commercial, educational, and municipal sectors. Toronto’s Maple Leaf Gardens,1 Brampton’s Alderlea Heritage Estate, and St. Catharines’ Canadian Hair Cloth Factory are recent inspirational illustrations of what has been achieved in Ontario. Heritage woodwork restoration, in particular, is a specialized area of this type of construction that is not fully understood by many general contractors, sub-trades, building owners, and even consultants. It is not, and should not be confused with, ‘renovation.’ The fact woodwork restoration is both an art and a science can make the specifications for this endeavour difficult to write. When the document does not clearly articulate the intent of the restoration, there is too much room for subjective interpretation. A clear specification—as well as the specified requirement of skilled, experienced, and qualified tradespeople—goes a long way to ensuring a successful outcome. This article defines heritage woodwork restoration/conservation, examines how it differs from standard construction, and explains why some projects go terribly wrong.

CONSTRUCTION CANADA WOOD DESIGN

Co-ordination and strategic project management of new build and heritage restoration, the bracketed area must be completed (at least to primer) before the excavation even begins for the new building. The new additions can be seen in the accompanying photos.

Finding the right team General contractors new to heritage work may not realize the potential challenges with this field, even at the estimating phase. Often, they do not have an estimator or project manager that possesses the necessary experience to undertake a project with a heritage component. It can be frustrating for an estimator who is used to preparing takeoff sheets based on readily available industry standard cost data. Heritage estimating requires at least some interpretation of the specifications. If a project has been estimated incorrectly, the chances of a successful compliance with the specification are minimal. Many tenders are now calling for a decade of specialist experience for heritage-related work, rather than the five years that seemed to be standard in the past. While this is

CONSTRUCTION CANADA WOOD DESIGN

certainly a progressive move, it is only relevant when the references and background information are thoroughly checked. This level of scrutiny gives a higher level of protection to both the building and the owner. The pre-qualification of general contractors with the financial capacity to handle challenging jobs, and that have worked on a number of heritage projects, is frequently seen. While the general contractors will not have the necessary heritage skills themselves, they can use both their experience with similar projects and network of subcontractors that have heritage expertise. A list of specialized subs is sometimes specified in the contract documents; this can help ensure the correct team is in place for the project. This is a common-sense approach as heritage restoration is fundamentally different from general construction and new buildâ&#x20AC;&#x201D;companies specializing in civil engineering infrastructure projects do not engage in residential construction or vice versa. Heritage restoration involves a great deal of custom work; almost none of the wood components can be readily purchased off the shelf or ordered from a catalogue. Further, the basic doctrineâ&#x20AC;&#x201D;especially in conservation of maximum retention of original materialâ&#x20AC;&#x201D;is in juxtaposition to new build work. Historical architectural woodwork replication and restoration requires a high degree of skill and education within the company providing these services and manufactured materials to the project. The firm must employ a team with a comprehensive range of experience and specialties. Traditional joinery, fretwork, carving, turning, wood conservation and restoration, and historic finish conservation, along with computerassisted design (CAD), are required to operate a successful historical architectural woodwork business. At least one member of the team should have expertise in artifact conservation, an extensive historical knowledge of styles, and a thorough understanding of proportion and the orders. The firm should also have an experienced building technologist that has the knowledge to understand new and historic building construction, as well as the building code and how it relates to each project. This kind of depth within the firm is essential to ensuring on-time and on-budget delivery of goods and services to the project, avoiding construction delays. All the team members should be educated and trained at the post-secondary level within their field. Moreover, there is a considerable outlay in specialized equipment including custom and adapted hand tools, standard and state-of-the art power tools and specific joinery machinery, and the tooling required for exact replication work. (This is infrastructure beyond what the average carpentry firm carries.) The company should ideally have an extensive reference library of both trade and pattern books of the period, other historical reference books, as well as the industry standard trade manuals and current building technology references, including the current edition of the applicable building code. It is extremely important due diligence be rigorously applied when pre-qualifying. There are many questions that need to be answered when determining the suitability of the specialist woodwork firm. Does the company really have 10 years of experience, and projects that substantiate this? Does it originate from a conservation/restoration background or at least from a finish carpentry apprenticeship? Did the staff serve formal apprenticeships or are they self-taught? Did they go to a recognized college that teaches the applicable skills, and did they continue their knowledge in heritage

CONSTRUCTION CANADA WOOD DESIGN

This moisture reading indicates good conditions of the application of paint and epoxy. The other photo shows well-executed Dutchmen patches to an area of a door jamb and casing that had been previously cut away.

after graduation?2 Does the company have the overall capacity to complete the work? An immediate check of the firm’s insurance status, as well as its clearance eligibility with the province’s worker’s compensation insurer, is easy to obtain indicators of that company’s ability to be working in the construction industry. (It is surprising how many small firms cannot produce these basic requirements.) During the project, at least one workshop inspection should be specified in the contract documents. This allows the consultant to gain crucial information about the firm and its ability to perform the work. The company should also be required to keep the approved craftsmen on the project for its duration. The specification of detailed mockups is one of the most useful ways to determine the ability of the heritage woodwork company. A mockup of an area of restoration that has been selected to encompass a number of skills should be assigned. Only once it has been approved, should work proceed. This area should then be kept as a reference for all other related work.

Wood, restoration, and water management Good heritage restoration is not just ‘scrape and paint.’ Old paint will often need removing, but this needs to be done with care to prevent unnecessary gouging and rounding off of

CONSTRUCTION CANADA WOOD DESIGN

An inappropriate adhesive was used to laminate the sill section above. Delamination took place within three years of the work’s completion.

moulding profiles to the heritage material. (Although this may sound obvious, it still needs to be written into the specification.) Existing damage (e.g. rot) to the woodwork will need to have well-executed Dutchmen that should be glued with suitable epoxy adhesives. The patch should be undetectable from 1 m (39 in.) or less. The Dutchman patch should not telegraph through the paint. When completed by a skilled person and installed at the appropriate moisture level with the right epoxy adhesive, it should have a long lifecycle provided future water management issues are addressed. Old reclaimed lumber of the same species and of similar low-moisture content should be used in patching wherever feasible. Material can often be harvested from the building itself, particularly when there is a new build component and some of the heritage material becomes ‘sacrificial.’ As mentioned, water management is critical to the survival of historic woodwork. Elevated moisture levels increase the likelihood of both rot and insect infestation. Wood

CONSTRUCTION CANADA WOOD DESIGN

The prolific use of car-body-filler was in violation of this project’s specification. This indicates the need for construction documentation to serve as a means of deterrent against this practice.

preservatives are often specified with the intention of addressing the problems of future rot and insect infestation. However, this should not be considered a total solution. The strategic design or adaptation of water management at the woodwork level must be considered in addition to the building’s overall moisture protection. Careful thought should be given to any use of wood preservatives that can leave the material in a condition unreceptive to application of epoxy and paint. The wood needs to have a coating applied that will adhere to the timber’s underlying cell structure. Certainly, the coating must penetrate the surface and not just sit on top of the wood. One must recognize the cocktail of chemical compounds may not mix as well as desired. Applying petroleum-based oil, plant-based oil, and synthetic resin to a plant cell structure is a delicate combination; the reliance is on these chemical reactions to form bonds for protection of the timber. Epoxy fillers are often specified to be used in restoration work. A two-part bisphenol A and F type with a phenol/formaldehyde reactor should be employed as an adhesive, and

CONSTRUCTION CANADA WOOD DESIGN

This is an area of a windowsill filled with car-body-filler—failure occurred within a year.

then used in combination with a high-grade fairing filler for the consolidation process. Latex-based fillers are not suitable for this work. While epoxies have a role to play in the restoration process, they should in no way be regarded as a substitute for skill. The manufacture of complete sections of mouldings, turnings, and carvings in epoxy is totally unacceptable and should not be condoned. If the company does not have the skill set to make these pieces in wood, they should not be doing the work.

Lifecycle of the repair It is important to look at the lifecycle of the repair project. This restored woodwork has to perform in a harsh environment in extreme temperatures and moisture levels. Car-body-filler is often used for repairing woodwork, but is inappropriate. An isobenzofurandione polymer-based product containing ingredients like oxide glass, salts with montmorillonite limestone, and chlorite is unsuitable for wood restoration. Obviously, wood should not be filled with something that does not come close to its modulus of elastically; the fact this product contains ‘stone’ should be a clear indicator of its unsuitability. Used prolifically throughout the painting and decorating industry, isobenzofurandione polymer-based materials are chosen because they dry quickly,

CONSTRUCTION CANADA WOOD DESIGN

Well-executed Dutchman patching, with clear-coat finish and colour-matching, successfully restored a split area.

allowing for same-day painting to expedite work (or cover up an inadequate job before the consultant can view it). The authors have seen in graphic detail what paint can conceal. In some cases, carbody-filler was used to make the cove moulding and 13-mm (½-in.) plywood for the flat fascia to ‘restore’ the cornice. (All this work was done by a painting contractor.) None of this restoration should have taken place until moisture content (MC) levels had been taken and were at satisfactory levels for the work to proceed. This would be nine to 15 per cent for exterior work, and five to 10 per cent for interior work in Ontario and Québec. Moisture readings should be taken at a few locations on the woodwork, particularly on horizontal areas. A pinless moisture meter that accurately checks the sub-surface

CONSTRUCTION CANADA WOOD DESIGN

MC should be used. Application of paint and/or adhesives must only be done when the moisture content is lower than the specified amounts stated. In the case of window sash, heritage glass will need to be carefully removed and labelled for re-installation; old glass must be harvested for broken/missing panes. Damaged edges on the putty rabbets will need to be addressed with Dutchmen. Rabbets should be primed prior to glazing, and glazing itself must be back-puttied and carefully tooled on the exterior, using linseed oil putty. The putty will need to skin over before it can be primed with an oil-based primer.

Documentation and pre-qualifications Documentation is also a major component critical to the successful completion of heritage woodwork restoration. This should be specified to take the form of a daily log book and a well- kept logical photo documentation record. The log should include a minimum of location references, as-built drawings and sketches, and the weather conditions (including air temperature and relative humidity [RH] readings). These readings should be taken into consideration before the commencement of the epoxy or paint application. Epoxy filling, consolidation, and painting when the surface is moist will ultimately lead to premature failure of the work and reduced lifecycle. The documentation should make clear the need to prequalify general contractors and the sub-trades they will use. A well-defined and comprehensive set of heritage specifications, and the careful selection of the section in which it is placed within the contract, are critical to ensure a positive outcome. Additional supervision will also be required, as well as high-quality material specifications. Further, mandatory site meetings for the general contractor (and sub-trades) should also be required. The specification must not be changed mid-project to suit the skill level of the bidder that has been awarded the contract. If the contractor cannot meet the specification required, it has not fulfilled its obligation under the contract—a clear indication the project should not have been bid on in the first place. Simply put, if the contract asks for a 152-mm (6-in.) slab-on-grade and a 102mm (4-in.) slab was supplied, the contract requirements were not met. The authors know a consultant who recently told a sub-trade, “You are going to have to come up to my level, as I am not going to lower my standards to yours,” in reference to a particular heritage roofing detail that was very clearly specified and accurately drawn in the contract. This consultant was extremely diligent in enforcing the contract specification.

Conclusion Ultimately, the successful outcome of a historical building restoration project depends on the strict enforcement of the correct specification, thorough attention to detail, and the skill level of the craftsmen preforming the work.

Notes 1

For a deeper look at this project, see the article, “Making History, Again: Repurposing Maple Leaf Gardens,” by Brian Burton in the September 2012 issue of Construction Canada. Visit www.constructioncanada.net.

CONSTRUCTION CANADA WOOD DESIGN

This is an example of both very poor workmanship and a total lack of knowledge in executing the work—note the heavy gouging of the surface (almost adze-like) and the very poor quality of the Dutchmen. Further, the uneven staining, colour, and treacle-like finish are completely out of context with the door’s Beaux-Arts architectural period. Dutchmen on stained and clear-coat work should be undetectable from a maximum of 300 mm (12 in). In reality, if well cut-in and carefully matched, they will be virtually indistinguishable. 2

On the note of education; this can be difficult to determine in Canada, unlike in England where the London City and Guilds certification is available. Given this multifaceted area of specialization has not even been clearly defined in Canada, how can we have an education program designed to train people for this? It is no wonder the industry is struggling to get this work done properly. This is a topic beyond the article’s scope, but it is something that needs to be addressed. It is misguided to think that a carpenter should be entirely responsible for this specialized area of work. However, at least for the portion of the work that does involve some carpentry, both Algonquin College (Ontario) and Nova Scotia Community College have good-quality heritage carpentry programs.

CONSTRUCTION CANADA WOOD DESIGN

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