Cross-laminated timber Preview

Revised reprint

Design and performance

Exemplars and case studies demonstrating excellence in CLT construction Highly illustrated with over 150 colour photographs and drawings Researched and written with input from leading CLT experts

Cross-laminated timber (CLT) is increasingly being used within residential and non-residential buildings. Offering a significant strength to weight ratio, improved installation speeds, reduced on-site waste and an inherent high standard of airtightness, CLT also has the advantage of being a renewable resource that can combine carbon sequestration with the design flexibility required in modern building practice.

This book has been written to cover the design and performance of CLT within construction.

Chapter 1 showcases its uses for architects and building designers. Chapter 2 focuses on design principles and Chapter 3 covers CLT performance, including structural design, fire performance, acoustics, thermal performance, durability, appearance, and sustainability.

Chapter 4 concludes the book with thirteen case studies based on several building types.

Cross-laminated timber Design and performance

Cross-laminated timber

Cross-laminated timber Design and performance

Highly illustrated with photos and technical drawings, this book demonstrates the versatility of CLT as a sustainable, engineered timber solution and will assist architects, engineers and their clients looking to work with this material.

Researched and written with contributions from Adrian Young, Patrick Hislop, Hugh Strange Architects, Arup, B&K Structures, Eurban, KLH UK, Ramboll, Stora Enso, Waugh Thistleton Architects, BM TRADA, and the Structural Timber Association.

BM TRADA, part of the Element Group, provides a comprehensive range of independent testing, inspection, certification, technical and training services. We help organisations to demonstrate their business and product credentials, and to improve performance and compliance. We help our customers to make certain that the management systems, supply chain and product certification schemes they operate are compliant and fit for purpose.

BM TRADA

CLT_Cover_230322.indd All Pages

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Contents

Introduction

7

Chapter 1 CLT and its uses 8 1.1 What is cross-laminated timber?

8 1.2 How is cross-laminated timber made?

10 1.3 How sustainable is cross-laminated timber?

13 1.4 What are cross-laminated timber’s key structural properties?

17 1.5 What are cross-laminated timber’s other key properties?

19 1.6 What does cross-laminated timber look like?

21 1.7 What can cross-laminated timber be used for?

23 1.8 How does cross-laminated timber compare to the alternatives? 26 Chapter 2 Design principles 2.1 Key facts 2.1.1 Speed of construction 2.1.2 A renewable resource 2.1.3 Less weight 2.1.4 Versatility 2.1.5 Structural uses 2.1.6 Thermal performance 2.1.7 Sound transmission 2.1.8 Vapour control 2.1.9 Airtightness 2.1.10 Appearance 2.1.11 Fire resistance 2.1.12 Moisture, durability and movement 2.1.13 Integrating building services 2.2 Example buildings and forms 2.2.1 Cellular loadbearing CLT 2.2.2 Glulam frames and CLT panels 2.2.3 Low-rise CLT structures 2.2.4 Crosswall 2.2.5 Hybrid

31 31 31 31 31 33 33 33 34 34 34 34 34 34 35 35 36 39 42 44 46

Chapter 3 Performance 3.1 Structural design 3.1.1 Structural forms and stability 3.1.1.1 Structural forms 3.1.1.2 Stability 3.1.1.3 Disproportionate collapse 3.1.2 Structural elements 3.1.2.1 Commonly used methods of analysis 3.1.2.2 Crushing 3.1.3 Wall panels 3.1.3.1 Pre-scheme design of walls 3.1.4 Floor panels 3.1.4.1 Pre-scheme design of floors 3.1.4.2 Vibration 3.1.5 Roof panels 3.1.5.1 Pre-scheme design of roofs 3.1.6 Hybrid and composite construction 3.1.7 Connections 3.1.7.1 Connection types 3.1.7.2 Screws 3.1.7.3 Nails 3.1.7.4 Analysis of fasteners 3.2 Fire

48 48 48 48 48 51 51 51 53 54 56 56 59 60 60 62 62 66 66 66 68 69 69

4 | Contents

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3.2.1 Fire resistance 70 3.2.1.1 Fire protection 71 3.2.1.2 Connections in fire 73 3.2.2 Compartment walls and floors 73 3.2.3 Resistance to surface spread of flame 74 3.2.4 Fire risk during construction 74 3.3 Acoustics 75 3.3.1 General 75 3.3.1.1 How CLT contributes to acoustic performance 76 3.3.2 Compartment walls and floors 77 3.3.2.1 Compartment walls 77 3.3.2.2 Party floors 79 3.3.3 Other walls and floors 80 3.4 Thermal performance 81 3.4.1 Thermal insulation 82 3.4.1.1 Common situations where thermal insulation is needed 83 3.4.1.2 Achieving thermal insulation with CLT structures 84 3.4.1.3 How to enhance thermal insulation of CLT 84 3.4.1.4 Thermal bridging 84 3.4.1.5 Insulating CLT and condensation risk 84 3.4.2 Airtightness 85 3.4.3 Thermal mass 87 3.5 Durability 87 3.5.1 Moisture 88 3.5.1.1 Wetting from weather 89 3.5.1.2 Contact with wetted surfaces 89 3.5.1.3 High humidity 90 3.5.1.4 Condensation 90 3.5.2 Moisture movement 91 3.6 Appearance 93 3.6.1 Exterior 93 3.6.2 Interior 94 3.6.2.1 Protecting the appearance of exposed CLT 95 3.6.3 Panel finish 96 3.7 Sustainability 97 3.7.1 Design and Access Statement 97 3.7.2 Carbon sequestration 98 3.7.3 Material 99 3.7.4 Transport 99 3.7.5 Delivery and erection 100 3.7.6 Disposal 101 Chapter 4 Case studies Case study 1 Bridport House, Colville Estate Case study 2 Strange House Case study 3 Dyson Centre Case study 4 Farnham Place Case study 5 Lancaster Institute for the Contemporary Arts Case study 6 Sky Health and Fitness Centre Case study 7 Ditchling Museum of Art + Craft Case study 8 Timber Lodge Case study 9 TNG Youth and Community Centre Case study 10 Kingsdale School Case study 11 Waingels School Case study 12 West Buckland School Case study 13 William Perkin Church of England High School

103 105 110 114 117 120 124 128 132 136 140 142 146 150 Contents | 5

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Introduction

The versatility of modern engineered wood products is leading to new and innovative timber buildings. Alongside timber’s well-known environmental advantages, the wider technical and performance benefits of products such as cross-laminated timber (CLT) and glued laminated timber (glulam) are now also being realised. By laminating layers of softwood together to form stable elements, producers are able to combine the traditional advantages of solid timber with new structural possibilities and accurate computer fabrication.

Pioneering timber experts have generously shared their expertise and experience in this book to assist in the wider understanding of the nature, potential uses and performance of CLT, and to communicate best practice to all building designers.

Following an introductory section on CLT and its uses (also available as a standalone document for use with clients), the authors describe aspects of design and performance in more depth for technical readers.

Exemplar buildings for CLT and hybrid glulam/CLT structures are examined.

Additionally, in the final section of the book, there are thirteen inspiring case studies demonstrating the application of CLT in a range of different building types.

Highly illustrated with relevant drawings and photographs, provides architects, building designers, engineers, contractors and construction managers with a useful, accessible resource they can consult for inspiration and technical guidance.

Nevertheless it is clear that the use of CLT as a building method is still evolving and future editions are anticipated in order to keep pace with developments and new practices.

Related CLT publications, available to buy at https://bookshop.bmtrada.com. include: •

Wood Information Sheet

:

•

Wood Information Sheet

:

•

GD10:

•

Worked example:

•

Case studies.

Introduction | 7

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CHAPTER 1

CLT and its uses

1.1 What is cross-laminated timber?

In recent decades, technological advances have led to the development of a new form of engineered timber, cross-laminated timber (sometimes called CLT or crosslam), that has transformed the opportunities for clients and architects in the construction of buildings, while retaining the age-old joy of working with this most natural and sustainable of materials.

Humankind has been building with wood since the beginning of civilization, leading in some cases to the development of extremely sophisticated cultures of timber construction. In Britain we have a very particular affinity with the material. In his 1955 Reith lectures titled ‘The Englishness of English Art’, Nikolaus Pevsner suggested this was perhaps born out of the importance of boat building to an island nation, ‘…English poetry has shown awareness of the sea around the island, and that hearts of oak are not only the ships, but also the mighty and ingenious roofs of the churches of England.’

Despite this, and with some notable exceptions, the Industrial Revolution, and the 20th Century in particular, saw a general decline in the pre-eminence of timber structures, and advances in steel and reinforced concrete technology led to their dominance as structural systems.

Factory-based innovations in Switzerland in the late 20th Century, however, established new techniques for processing the raw material of wood to produce new forms of engineered timber. By laminating layers of softwood together to form stable elements, producers are now able to combine the environmental and aesthetic advantages of traditional timber construction with new structural possibilities and accurate computer fabrication.

Figure 1.1 (above) Long House, Hampshire English architecture has a long tradition of using timber as a structural building material. In this image a stack of crosslaminated timber panels awaits erection adjacent to a traditional timberframed house

Figure 1.2 (right) Architect Place Architecture Client Private Timber structure Eurban/Merk Timber Timber superstructure engineer Eurban Photograph © EURBAN

Mountain Shelter, Austria Cross-laminated timber was first developed in central Europe in the 1990s. Here, a helicopter delivers lightweight, prefabricated panels to a remote alpine location for rapid and simple siteassembly

Architect Hermann Kaufmann Client German Alpine Club Timber structure Binderholz Photograph Hermann Kaufmann

8 | CLT and its uses

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CHAPTER 2

Design principles

2.1 Key facts In the more general aspects of CLT construction were introduced, such as the basic materials, the method of manufacture, the environmental merits and the construction costs of the method. A number of example buildings demonstrate the versatility of CLT construction. CLT construction has been used in Europe for some time and is rapidly growing in popularity in the UK. It has already been used for many types of building, from individual houses to multi-storey flats, and from primary schools to offices and sports buildings. contain more detailed information for designers, whether architects or engineers, who are considering using this method of building.

This chapter is about the issues designers must consider when deciding on materials and structural form, while deals with performance. But at this stage it is particularly important to note a fundamental characteristic of the product – speed of construction.

2.1.1 Speed of construction For many specifiers, the biggest advantage of CLT is the speed of construction. It offers an alternative form of loadbearing panel system to pre-cast concrete, with the same potential for multi-storey construction and prefabrication. Temporary props can be removed as soon as the slabs are installed, allowing follow-on trades to start work, thereby making programme savings in the process. See

2.1.2 A renewable resource CLT construction offers a particular advantage over concrete and steel in that timber is a renewable resource, while steel and concrete are not. Like all wood components, a substantial amount of carbon is locked into the panels for the life of the building. explains this in more detail.

2.1.3 Less weight CLT has a higher strength to weight ratio than solid concrete, reducing foundation requirements, craneage and transportation costs. For instance, Bridport House in London was constructed over the site of a large and vulnerable brick sewer that is incapable of supporting high foundation loads.

Using CLT enabled the construction team to keep the mass of the building down while at the same time adding additional storeys.

The theatre facilities and box office in Regent’s Park, described in , provide another example that illustrates this point. Here, the use of CLT Design principles | 31

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One advantage of using glulam or other wood-based materials in conjunction with CLT panels, rather than steel or concrete for framing, is that structural connections between the wood-based materials can be relatively simple, only requiring screws, bolts or nails. There is also the advantage that both components will react in a similar manner to changing environmental conditions.

Similar thermal properties will also substantially reduce the risk of the thermal bridging through external walls that can sometimes occur with steel or concrete structures. There will also be a similar reaction to fire in both panels and framing in that they will both be protected from fire by charring in a similar manner if designed appropriately.

Because CLT panels can be made in large sizes, unusual shapes or occasionally even bent into curved forms, they have been frequently used on projects with non-orthogonal structures such as three-dimensional lattice roofs that can be pyramid, folded, vaulted or dome-shaped in form. These structures can be made up with CLT roof panels alone or in conjunction with a glulam framing. In either case the CLT panels can be easily cut to the complex shapes and edge profiles required. shows an unusually complex-shaped swimming pool roof simplified by composite construction of stressed-skin CLT panels comprising thin CLT with whitewood rafters and glulam beams. See ‘ ’ case study12 for details.

Figure 3.21 Stressed-skin CLT roof panels at Alfriston School Drawing Duggan Morris Architects

Performance | 65

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CASE STUDY 7

Ditchling Museum of Art + Craft

Introduction Figure 4.29 The listed late-18th Century cart lodge has been restored to house a café, shop, and a new entrance Photograph Tim Brotherton and Katie Lock

In the years before the First World War, the typographer and sculptor Eric Gill and the graphic designer Edward Johnston (best known for his sans serif typeface for London Underground), moved to Ditchling, a rural village on the Sussex Downs above Brighton. Influenced by the teachings of William Morris, they formed a loose community with other artists and craftspeople, including printer and poet Hilary Pepler, poet and artist David Jones, hand weaver Ethel Mairet and silversmith Dunstan Pruden. The community eventually dwindled but the tradition of creativity remained and in 1985 a small museum, celebrating the work of its famous artistic residents, was set up in Ditchling’s Victorian village school.

128 | Case studies

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Revised reprint

Design and performance

Exemplars and case studies demonstrating excellence in CLT construction Highly illustrated with over 150 colour photographs and drawings Researched and written with input from leading CLT experts

Cross-laminated timber (CLT) is increasingly being used within residential and non-residential buildings. Offering a significant strength to weight ratio, improved installation speeds, reduced on-site waste and an inherent high standard of airtightness, CLT also has the advantage of being a renewable resource that can combine carbon sequestration with the design flexibility required in modern building practice.

This book has been written to cover the design and performance of CLT within construction.

Chapter 1 showcases its uses for architects and building designers. Chapter 2 focuses on design principles and Chapter 3 covers CLT performance, including structural design, fire performance, acoustics, thermal performance, durability, appearance, and sustainability.

Chapter 4 concludes the book with thirteen case studies based on several building types.

Cross-laminated timber Design and performance

Cross-laminated timber

Cross-laminated timber Design and performance

Highly illustrated with photos and technical drawings, this book demonstrates the versatility of CLT as a sustainable, engineered timber solution and will assist architects, engineers and their clients looking to work with this material.

Researched and written with contributions from Adrian Young, Patrick Hislop, Hugh Strange Architects, Arup, B&K Structures, Eurban, KLH UK, Ramboll, Stora Enso, Waugh Thistleton Architects, BM TRADA, and the Structural Timber Association.

BM TRADA, part of the Element Group, provides a comprehensive range of independent testing, inspection, certification, technical and training services. We help organisations to demonstrate their business and product credentials, and to improve performance and compliance. We help our customers to make certain that the management systems, supply chain and product certification schemes they operate are compliant and fit for purpose.

BM TRADA

CLT_Cover_230322.indd All Pages

23/03/2022 14:23:29