Landscape and exteriors Cladding
Changes to the tests and requirements for fire and cladding
Mostafa Jafarian explains the regulatory developments and how these affect timber cladding.
A
lthough 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).
www.trada.co.uk
Timber 2021 Industry Yearbook
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