30 minute read
Service life performance of wood in construction
Ed Suttie reveals how a new project is calculating the durability performance of wood.
When we buy a house, it is rare that we scrutinise durability aspects of performance in relation to how long the whole, or components of the whole, will last or function. We understand a need for upkeep and maintenance, and we may make decisions based on perceptions or experience and avoid surprises by engaging a professional surveyor or take comfort from new home warranties. In the construction industry, we need to understand durability to design a house, which raises the question ‘How long does a house last?’
What is a forever home?
Victorian houses, among others, have transitioned into our national conscience as an important part of our urban landscape, many afforded conservation status, and as such they might last ‘forever’ as we invest significantly in maintaining and upgrading them. However, many house types, and perhaps many new-builds, may never be valued as conservation-worthy, through loss of functionality or undesirableness, and be lost sooner, such as a poorly designed post-war housing development that is demolished after only 40 years in service.
More empirically, whole building environmental assessment methodologies, for example BREEAM1 and the former Green Guide to Specification,2 set a lifetime for a home that reflected the study period for the life-cycle assessment (LCA). This lifetime was set as 60 years, a little more than two typical mortgage cycles. This enabled comparison of environmental impact for components that may be used for the same function but which are made of different materials, and with different maintenance and replacement intervals.
The service life of the components (windows, doors, floor cassettes etc) therefore became the focus of interest and significantly affected environmental assessments such as LCA, and latterly environmental product declaration (EPD). A component that needs to be replaced twice in the 60-year study period would have a much greater lifetime environmental impact than a component that only had to be replaced once, or even not at all, during the 60 years. >>
Software tool developed by the CLICKdesign project. Photo: Ed Suttie
Performance-based specification
Service life planning and performance classification are core issues in construction, underpinning product specification and use. The absence of easily accessible durability and performance-based specifications for wood currently limits opportunity. Concrete, steel and polymeric sectors deliver software to architects and other students of construction, enabling performance-based specification and consistent teaching of design best practice.
The need for service life data
Building Information Modelling (BIM) maintains information in a suitable format so that better decisions can be made about planning, design, detailing, occupancy and end of life. The life cycle data management in BIM needs service life data and functionality data for components and assemblies, as well as information on changes to the asset during its lifetime. BIM therefore requires durability service life data and will, in future, determine decision-making regarding component and structure selection based on performance.
Service life of components is determined from models of degradation of the component in its exposure and use conditions, often combined into a factor method such as described in ISO 15686.
Wood in construction
We have a cultural legacy of wood in construction that reminds us of the enduring possibilities for wood, if knowledge is applied – including species and material qualities, design details and construction skills, knowledge of local conditions, and climatic and other challenges. How long do wood products last? Well, of course, it depends – a block of wood on my desk will last forever if the building around my desk and internal conditions remain the same as they are now.
However, durability service life data can be fragmented and complex to analyse. The performance of a wood product in service is the combination of the material resistance (durability, coatings) and the exposure (climate, design, environment). If the exposure dose is less than the material resistance, the product endures until the exposure dose exceeds the material resistance (for example, as it weathers) and onset of decay or significant surface colour change occurs (the limit state). This does not happen comprehensively in Europe for wood, although specific initiatives do exist, for example:
• TRADA’s National Structural Timber Specification (NSTS)3 • UK Structural Timber Association guidance4 • German Carpenter Association’s Guideline on Building
Facades, Terrace decking and Balconies.5
But this specification gap, and the fact that technical specifications for performance are increasingly required for BIM and LCA, has driven the development of ForestValue6 project CLICKdesign. The project is developing a performance-based specification protocol for wood in construction and is providing a software tool for service life performance specification for planners and architects.
Service life
The established specification of wood durability is not performance based. Service life is referred to as unquantified and in an ambiguous way, using terms such as ‘reasonable working life’ or ‘satisfactory performance’. Timber engineers using Eurocode 57 find that this ineffectual language is of little value.
For performance modelling of wood products, biological agents (mould, decay fungi, termites and other insects) need to be considered. First attempts were prepared using various models that had been derived from previous European research projects. Good progress has been made during more recent years in service life planning and performance prediction of wood-based components and structures, but, as repeatedly became evident, the complexity of performance is still not captured in these processes and it remains ‘on the shelf’ rather than in use.
The foundation of previous work has now been reviewed and this has enabled a running start to the CLICKdesign >>
‘Hunting tower’ test rig capturing data on local climate variation and vegetation. Photo: Christian Brischke, University of Göttingen, Germany
project, which has generated data on significant missing features related to performance, such as splash water, cracks, vegetation and topography. In addition, project CLICKdesign includes a focus on robust time forecasting of aesthetic changes on wood surfaces – a vital component of functionality for exterior wood cladding and decking.
CLICKdesign project
The tool is based on a numerical model that enables the user to zoom in on the location of their building or structure in Europe and automatically upload average climatic data. This provides default moisture content data for a Norway spruce board and a service life figure at that location. By implementing selections for design details (end grain, moisture traps, joints, shelter from overhangs), topography and shading, further impacts on the moisture content and service life are revealed. If the outcome is not acceptable, different materials of different material resistance can be selected. This helps educate users as they can directly see the impact of their decisions on the moisture content and service life.
The aesthetics model that combines with this unfolds the surface of the building to create a UV surface map and, combined with material data, provides a simulation of surface wood appearance for predicted rain cycles. Architects can see how their timber clad design will change in appearance with time.
The next step is to integrate a termite and insect measure into the durability and aesthetic functionality, to make the tool pan-European. The tool then be made more widely available in 2021 for piloting with groups of specifiers and architects.
Conclusion
Wood is a versatile construction material, which can make a highly significant contribution in tackling the climate emergency – through forest growth and by locking carbon into buildings. This may be achieved by specifying timber products in place of other construction materials that have greater impact on the environment. However, of equal importance is that the wood product must perform its function for a satisfactory period (the service life), ideally the lifespan of the building.
Therefore, as we take custodianship of this incredible carbon store, it would make folly of nature’s good work and our endeavours if it were inappropriately specified for the exposure challenge it will face over its lifespan, and as a result failed prematurely with the resulting economic and social consequences.
As data is central to decision-making, the information about the service life for wood products is a foremost question. To fulfil the maximum potential of the contribution of timber in construction to the United Nations Sustainable Development Goal 13 (Climate Action), wood products must deliver long-term carbon storage through performance-based specification. n
About the author
Ed Suttie Research Director Centre for Sustainable Products BRE
Further information
To find out more, email Ed.Suttie@bregroup.com or visit www.bregroup.com/services/research/clickdesign
Further reading
• WIS 4-28 Durability by design, BM TRADA, 2019 • Design life for wood and wood-based products, BM TRADA, 2018
References
1. www.breeam.com 2. www.bregroup.com/greenguide 3. National Structural Timber Specification (NSTS) V2.0, 978-1-909594-61-6, BM TRADA, 2017 4. www.structuraltimber.co.uk 5. Holzbau Deutschland: Home (holzbau-deutschland.de) 6. https://forestvalue.org 7. BS EN 1995, more commonly known as Eurocode 5 or EC5, is the standard for structural timber design.
Alternative UK timber species
Steven Adams and Dan Ridley-Ellis discuss the findings of a recent research project into the properties and potential uses of lesser-used timber species in the UK.
European silver fir logs being marked up prior to cutting into test specimens. Photo: Edinburgh Napier University
The UK’s commercial forestry is based largely on one species, Sitka spruce, which provides wood fibre for use in a wide range of uses, including construction, pallets and packing, fencing, panel products and paper. There are other important economic species, such as Norway spruce, Scots pine, larches, and Douglas fir, but a little more than half of the total volume is Sitka spruce because this species grows and processes so well.
With more than 15 years of research at Edinburgh Napier University, the properties of these timbers are now well known, but this does not necessarily provide certainty for the future. Just these few species, together with two more pines (Corsican and lodgepole), account for as much as 95% of the total home-grown softwood available for harvest, which raises concerns about the resilience of the forest, and the industries and livelihoods that depend on them, against the effects of climate change, pests and diseases.
Disease and diversity
There is now a different, and more personal, perspective on the need to keep a disease outbreak under control, but there is also no shortage of high-profile examples for trees too, such as ash dieback and Phytophthora ramorum, which are causing enormous damage in the UK, and Xylella fastidiosa, pinewood nematode and spruce bark beetles in Europe. One way to protect forests, which also brings many other benefits for modern multipurpose forestry, is to plant a much wider range of tree species – but how can we prepare our wood products industries for a more diverse raw material?
UK forests already have a number of other tree species that are currently under-managed for the production of wood, but which could potentially be brought into the supply chain in the near future, though the real challenge is preparing for what is being planted now. There is information in books and databases about these other species when grown in other countries, but data is sparse about what the properties would be like when grown in the UK (except that there is a good chance that they will be different), or how suitable they would be for processing in mills that have optimised their operation for the relatively small list of current species. >>
Research project
A study by the Strategic Integrated Research into Timber (SIRT) project took a preliminary look at certain potential alternative species, to gauge what properties could be expected from growth in UK forests, and how they might complement the existing commercial species for the wood processing industries. Initially, seven species with promising forestry potential were selected through consultation with the Forestry Commission (as it was then known), and members of the SIRT project management board and sponsors representing the forestry industries.
The study covered Pacific silver fir (Abies amabilis), European silver fir (Abies alba), grand fir (Abies grandis), Japanese red cedar (Cryptomeria japonica), Serbian spruce (Picea omorika), sycamore (Acer pseudoplatanus) and silver birch (Betula pendula). A previous study, with additional funding from the Scottish Forestry Trust, covered Norway spruce (Picea abies), noble fir (Abies procera), western red cedar (Thuja plicata) and western hemlock (Tsuga heterophylla). A Forest Research project also enabled some testing of Nordmann fir (Abies nordmanniana).
Some of these species had, so far, only been grown in small amounts, but thanks to the work of the Forestry Commission there were some reasonably representative stands in forest gardens and other experimental plots. Nevertheless, it requires a large amount of testing across several sites to properly characterise a timber species for commercial production from a particular geographical origin, so the data that follows can only be an indication of potential, pending more comprehensive study. This was especially true, even for the very common species birch, because the available trees, not being managed for timber, were too small to produce many timbers of the 100mm x 50mm size we used for evaluating strength.
The European grading system for structural timber is based on density, strength and stiffness (usually in bending), and it is usually one of these that will limit the achievable grades. For example, Sitka grown in the UK tends to be limited by stiffness when grading to standard BS EN 3381 strength classes, but other species can be limited by strength (such as UK-grown Douglas fir) or by density. This preliminary testing is enough to indicate the most likely limiting property, but the strength class estimates are more tentative. >>
The timber is broken in a bending test to obtain strength and stiffness data. Photo: Edinburgh Napier University
Outcomes
Softwoods
Results of this study indicate that UK-grown Japanese red cedar, which is one of the most economically important species in Japan (where it is known as sugi), would struggle even to make C14, due to low stiffness and a remarkably low mean density of just 310 kg/m3 . 2 This does not mean that it does not have its uses, where its low weight could come in handy for use as studs in partition walls, or even super-lightweight crosslaminated timber. It is an attractive wood, but also rather soft.
European silver fir. Photo: Edinburgh Napier University
If grown in the UK, four of the North American species – grand fir, western red cedar, noble fir and Nordmann fir – also look like they might not be able to achieve the usual UK market strength class, C16, with high grading yields, the first two due to low stiffness and the second two due to low strength. This, however, might well be due to the limited testing, particularly for grand fir and Nordmann fir. The other properties measured for grand fir showed more promise, with strength suitable for C16 and density suitable for C18, and similarly with Nordman fir, where stiffness was equivalent to C18 and density C30. The other two North American species look like they would be able to achieve viable C16 yield for grading, if grown in the UK. Pacific silver fir is limited by its density and western hemlock by its stiffness. However, western hemlock, being rather similar to Sitka but with higher density, is a good candidate for blending in with existing British spruce supplies. Pacific silver fir, with strength and stiffness both looking to be around the C18 mark, might have potential for lightweight construction, even compared to Sitka spruce – which was historically favoured for building aircraft.
Three UK-grown European species of conifer were included – of these, European silver fir looks limited to C16 by stiffness, but strength and density again far exceeded this grade (C20 and C27 respectively). Serbian spruce looks to be limited to C16 by strength, but had good stiffness (C18) and density (C40). Norway spruce is already known to be similar to Sitka, which grades very well to C16, perhaps with slightly better stiffness and strength.
Many of these conifer species look like they could have potential to be blended in to the existing C16 ‘British spruce’ market, ideally by mixed processing, subject to adequate grading approaches. This is encouraging, as relatively small amounts of these species could start entering the mainstream markets with little disruption.
Hardwoods
Two hardwood species, sycamore and birch, were looked at to see if they could be the equivalent of and be graded along with the conifers. Both species were found to have good properties; with sycamore, stiffness is the limiting factor and would fit the ‘softwood’ grade of C18. For birch, both the stiffness and strength are limiting factors, but fit the >>
high grade C40. However, it proved difficult to get enough birch of the dimensions required, which not only meant that only limited testing could be carried out but also that it may be difficult to find enough suitable material for processing. Density for both these species is, unsurprisingly, much higher than the softwood grades require, but it is also not enough to grade well into the hardwood D-classes where it would become the limiting property, reducing the declarable design strength and stiffness.
Industry survey
At the same time as this research, a survey was carried out asking for the thoughts, opinions and experience of sawmillers with these alternative species. The results showed that, while there is little or no experience of using some of these species, such as Japanese cedar, Pacific silver fir and Serbian spruce, this did not preclude everyone from saying that they would not be open to using them if they became available in the future.
A stool made from birch and sycamore, reclaimed from the broken test specimens. Photo: Edinburgh Napier University There was some experience of the other conifer species, European silver fir and grand fir, with the latter being the least popular due to the presence of large knots and cracks, for example, which weaken the wood and create processing problems. Birch and sycamore were also known, with both species receiving a favourable opinion.
Thoughts for the future
The information gained from this research into the mechanical properties of alternative timber species, together with information from the concurrent survey gathering the thoughts and experiences of professionals using these species and working within the industry, will help to inform future research. This research will feedback to industry to help make informed decisions for new planting and preparing the UK’s timber industry for the future. n
About the authors
Steven Adams Research Fellow Edinburgh Napier University
Dan Ridley-Ellis Head of the Centre for Wood Science and Technology Edinburgh Napier University
Further information
Research into properties of several species mentioned in this article can be found at: www.forestresearch.gov.uk/research/ timber-properties-of-noble-fir-norway-spruce-western-redcedar-and-western-hemlock-grown-in-great-britain
Further reading
WIS 2/3-67 Specifying British-grown timbers, BM TRADA, 2017
References
1.BS EN 338:2016 Structural timber. Strength classes, BSI
2.Adams, S. H. and Ridley-Ellis, D. J., ‘A brief look at alternative tree species in the UK’, Proceedings of the 16th
Annual Meeting of the Northern European Network for Wood
Science and Engineering – WSE2020, 1–2 December 2020
Brimstone cladding test site
Tom Barnes reports on a project that hopes to provide a better understanding of this innovative British product.
The Sylva Foundation Wood Centre in Oxfordshire. Photo: Sylva Foundation
In 2015 a prototype of thermally modified British hardwood cladding was installed at the Sylva Foundation Wood Centre in Oxfordshire, as part of a feasibility project by Grown in Britain. The Sylva Foundation is an environmental charity, providing silvicultural training and workplaces for woodworking enterprises.
Five years later and, after much testing and refinement to the product, a new batch is being installed by Vastern Timber under the brand name Brimstone. This cladding and joinery at the Sylva Wood Centre is the latest addition to what has become a long-term test site for this innovative material.
The project
The aim of promoting under-utilised British timber aligns with Sylva’s goal of ‘helping trees and people grow together’. To create the latest test site at the Sylva Wood Centre, Vastern Timber supplied over 100 square metres of Brimstone cladding in three different species. Windows and a door were produced by George Barnsdale, using thermally modified ash.
The front elevation, which faces west, has been designed to look relatively consistent, although it includes three species, three different profiles and three different fixing methods. The three species used are ash, sycamore and poplar, all of which have been thermally modified for external use. This installation of the cladding was the final stage of a large redevelopment project of the old grain store at the Sylva Wood Centre, providing new workspaces for woodworking enterprises and skills training. The remainder of the building was clad in British larch feather-edge, chosen because of its value for money and provenance.
Brimstone cladding has been installed on hundreds of commercial and residential buildings, but it is often difficult to gain access regularly and for a long period of time. The installation at the Sylva Wood Centre allows continuous access to view the product and monitor changes. It is also rarely the case that one installation will include different cladding types alongside each other for comparison purposes.
All wood looks great on day one, but it is far more relevant to know how the products will perform over time. This installation creates an accessible long-term research and display site in an interesting location where the cladding and joinery can >>
We use intense heat to reconfigure traditional British hardwoods. No chemicals. Nothing nasty. Just a more durable, stable and consistent material for decking, cladding and joinery.
Transforming British Woods
By using British species, we’re increasing the demand for native broadleaf woodlands. This supports local species and rural jobs, while reducing the environmental impact of global transportation.
For product advice and sales
Vastern Timber: 01793 853 281 sales@vastern.co.uk www.brimstonewood.co.uk
be monitored over many years. Brimstone has been tested to destruction in the lab but there is no better evidence than having the product in situ on a building for the long term. The Sylva Wood Centre development adds to the wealth of data covering durability, stability and consistency.
Thermal modification can be used to transform under-utilised, locally grown species such as ash, poplar and sycamore into a durable, stable cladding suitable for a wide range of projects. The process uses nothing but extreme heat under controlled conditions to alter the cell structure of the original wood. The effect of the transformation is to make the wood more durable, stable and consistent. Although many wood species respond well to thermal modification, white hardwoods work particularly well. It is also a happy coincidence that these same white hardwoods are currently not in vogue and are consequently hard to sell in their raw form.
Five years of testing and development
The first thermally modified British ash and sycamore were installed at the Sylva Centre in 2015 as part of a project with Grown in Britain, the organisation dedicated to supporting the use of British timber. The original batches have weathered nicely and show no signs of decay or distortion.
Since the first material was installed, so much has been learnt about the material; how it performs and the best ways to install it. Although thermal modification is now a well-established process, investment in testing has helped to determine physical and performance metrics specifically for these products rather than relying on generic data. The species used have achieved Class 1 Durability for out-of-ground use in lab-based testing and mechanical tests have demonstrated a minimum of 50% improvement in dimensional stability.
Environmental Product Declaration
To discover the environmental impact of thermal modification, a detailed life-cycle analysis of Brimstone was commissioned.
Environmental Product Declaration. Source: Sylva Foundation
The Environmental Product Declaration (EPD) was an extensive process, modelling the greenhouse gas removals and emissions in the life cycle of Brimstone, from the growth of the sapling to the eventual disposal of the product at the end of its useful life.
This rigorous analysis of Brimstone enables like-for-like comparison with similar products, but the key benefit of the process was gaining a better understanding of the impact at each stage of production and the identification of potential impact reductions in the future. >>
Windows and a door were produced by George Barnsdale, using thermally modified ash. Photo: Sylva Foundation
Brimstone joinery by George Barnsdale
As well as supplying the Sylva Centre cladding, Vastern Timber worked with George Barnsdale Joinery to produce timber-framed windows and doors made of Brimstone ash for this project. This is the first commercial site to house joinery made from Brimstone timber, and it was the first joinery to result from this association with George Barnsdale.
While confidence has grown in understanding Brimstone as a cladding and decking material there is a lot to learn about its performance and suitability for joinery applications.
George Barnsdale is a family owned firm with a proud history and a commitment to innovation and sustainable development. It has a commitment to research and development, and the manufacture of high-quality products from British-grown timber.
A growing body of knowledge
This new installation of Brimstone cladding and joinery at the Sylva Wood Centre is the latest step in a quest to test, observe and fully understand the characteristics of Britishgrown, thermally modified timber. The Brimstone cladding and joinery will be monitored over time and the outcomes will contribute to the growing body of knowledge and, in turn, the advice that can be offered to architects and specifiers for future projects. n
About the author
Tom Barnes Managing Director Vastern Timber
Further reading
• WIS 2/3-63 Modified wood products, BM TRADA, 2017
• External timber cladding, ISBN 978-1-909594-005, TRADA
Technology, 2013
Changes to the tests and requirements for fire and cladding
Mostafa Jafarian explains the regulatory developments and how these affect timber cladding.
Although timber is historically one of the most commonly used materials for construction, the current climate emergency, and as a result the focus on sustainability and the reduction of carbon dioxide emissions, has prompted an increase in the specification of timber for construction projects.1-3 Advances in timber technology have also enabled designers to use hybrid timber solutions not only for low-rise construction but also for medium-to-high-rise construction (such as the 58m-tall Brock Commons Tallwood House in Vancouver, Canada,4 the 49m-tall The Tree in Bergen, Norway, the 33m-tall Dalston Works in London, UK and several others).
Despite their advantages, timber structures are vulnerable when exposed to fire if not adequately protected.5 Fire safety of timber construction and the risks in terms of fire resistance and reaction to fire are specified in fire safety regulations.6, 7
Regulatory changes
Following the tragic fire at Grenfell Tower, several standards have been subject to reviews and redevelopment, which has had an impact on the timber industry. In England and Wales this includes an amendment to Building Regulation 7 – Materials and Workmanship, the review of the Approved Document B (AD B),6 BS 84148 and development of BS 9414.9
The review of AD B led to amendments and clarifications. The main part subject to revision was part B4 of AD B dealing with external fire spread and the inclusion of the amendment text from Regulation 7. As a part of those changes, Regulation 7(4) defines so called ‘relevant buildings’, which means a building with a storey height of more than 18m* above ground level that contains one or more dwellings, an institution, or a room for residential purposes**. For this type of construction the external walls or specified attachments must be made from materials
Figure 1: Provision of the materials for external wall systems. Source: Building Regulations, ‘Approved Document B: Volume 2 – Buildings Other than Dwelling Houses’, National Building Specification, MHCLG, 2019
with a reaction-to-fire classification of A2-s1, d0 or better (when classified to EN 13501-110)***. For non-relevant buildings such as hostels, hotels or boarding houses with a storey height over 18m or other buildings with a height under 18m, the external wall can still be constructed with materials that do not achieve class A2-s1, d0 or better, provided that they comply with the recommendations given in paragraphs 12.3 to 12.9 of AD B (which offers guidance for external surfaces, materials and products, cavities and cavity barriers). The provision of the acceptable materials is given in paragraph 12.5 and table 12.1 (see Figure 1). The alternative route, as shown in paragraph 12.3 b, is to meet the performance criteria given in BRE report BR 135 for external walls using full-scale test data from BS 8414-1 or BS 8414-2.11 >>
* This height does not include roof-top plant areas or any storey consisting exclusively of plant rooms. The height is also under review and may be lowered further. ** This article discusses the changes applicable in England and Wales; similar regulations and guidance are published in Scotland with the limit set at 11m. Northern Ireland is likely to follow
England and Wales in future. *** Some exemptions exist for component parts that are documented in Regulation 7(3).
How is timber cladding affected?
The new recommendations mean that timber cladding, if treated to have an improved flammability performance, can achieve Class B at present but not A1 or A2, and must be tested to BS 8414-1 or BS 8414-2 (if used for construction above 18m for non-relevant buildings); see Figure 2. Aside from those points that directly affect technical aspects of the test, the latest version of the standards requires labs to provide more detailed information about the:
• observations during and after the fire test • installation and installers of the cladding system.
BS 8414-1 or BS 8414-2 are a series of well-known, largescales tests developed in the UK to determine the performance of non-loadbearing cladding systems under fire conditions. These tests are among the most stringent fire tests, duplicating a post-flashover fire scenario in a room with a total heat output of 4500MJ over 30 minutes at a peak rate of 3±0.5 MW. Those points are particularly important because the performance of a cladding system is significantly affected by the detailing and installation of the key elements of the system.12
The new standard
These standards have been reviewed and the latest versions are currently being applied. Although not subject to fundamental changes, there were some additional points. These include:
• fixing the height of the rig (where previously only a minimum was stipulated) • an additional measurement level closer to the top of the rig (that can gather further information and can be used for more detailed classification of the cladding) • specification of the block work required for BS 8414-1 test. While the new regulations do limit the use of timber for construction above 18m, if the recommendations of the fire safety codes are followed (for example treatment of timber to achieve Euroclass B-s3,d0) and if the timber is appropriately and robustly detailed for construction, it could be tested to the relevant part of BS 8414 to demonstrate compliance. However, even within a single structure the detailing and cladding systems could vary. Therefore, as part of the review of the standards, the Government commissioned the development of a new standard BS 9414.
BS 9414 was developed with the remit of having harmonised rules for extending the scope of application of cladding systems tested to the BS 8414 test series. It would also ensure that a new system could not record temperatures higher than the tested system. The new test regime will allow for previously tested products to remain valid, while extending the scope of the test to allow testing of newer products with more applications. This approach not only accommodates the need for the practical aspect of the test, but also makes sure that the change in detailing would not have an adverse impact on the overall performance of the system. >>
Open Academy, Norwich. Photo: Hufton+Crow Photography
Conclusion
Although the changing regulatory environment has had an impact on the use of timber cladding systems, the new regulations still allow for these to be used where the detailing is robust and fire test evidence is provided. The regulations will ensure the fire safety of the end-use product before they are used as a part of a construction. n
About the author
Dr Mostafa Jafarian Principal Certification Engineer – Facades & Structures Warringtonfire
Further reading
External timber cladding 4th edition will be published in 2021 and will be available to buy from https://bookshop.trada.co.uk.
References
1. Structural Timber Association, ‘Timber as a structural material – an introduction’, Structural Timber Engineering
Bulletin, 1, pp1–6, 2014 2. Loss, C. and Davison, B., ‘Innovative composite steeltimber floors with prefabricated modular components’,
Engineering structures, 132, pp695–713, 2017 3. Campbell, A., ‘Mass timber in the circular economy: paradigm in practice?’, Proceedings of the Institution of Civil Engineers –
Engineering Sustainability, Thomas Telford Ltd, 2018 4. Jackson, R., ‘Project focus: The TallWood House at Brock
Commons, Vancouver’, The Structural Engineer: Journal of the Institution of Structural Engineers, 96(10), pp18–25, 2018 5. Gerard, R., Barber, D. and Wolski, A., Fire safety challenges of tall wood buildings, National Fire Protection Association, 2013 6. Building Regulations, ‘Approved Document B: Volume 2 –
Buildings Other than Dwelling Houses’, National Building
Specification, MHCLG, 2019 7. Building Regulations, ‘Approved Document B: (fire safety) volume 1: Dwellings’, National Building Specification,
British Standards Institute: London, 2020 9. BS 9414:2019 Fire performance of external cladding systems. The application of results from BS 8414-1 and BS 8414-2 tests, British Standards Institute: London, 2019 10. BS 13501-1:2018 Fire classification of construction products and building elements, in Classification using test data from reaction to fire tests, British Standards Institute: London, 2018 11. BS 8414-2:2020 Fire performance of external cladding systems. Test method for non-loadbearing external cladding systems fixed to, and supported by, a structural steel frame,
British Standards Institute: London, 2020 12. Jafarian, M. and Murrell, J., ‘Testing façade systems to BS 8414 test series’, Gulf Fire, 2020
