Earlier this month, the government revealed that all residential buildings over six storeys will be covered by its new fire safety regime, after Housing Secretary Robert Jenrick announced in January ‘the biggest change in building safety for generation’, including a new regulator, changes to height limits and new consultations.
‘Clarified and consolidated’ advice for building owners, proposals to extend the combustible materials ban and a consultation to lower mandatory sprinkler limits were launched, while a construction expert was appointed to review timescales and ‘identify what can be done to improve pace in the private sector’ in terms of cladding removal.
Mr Jenrick stated that the new regime would apply to all buildings six storeys or taller ‘even when they are below 18m in height’, a change from the government’s previous perspective that the regime would ‘only cover buildings at or above 18m in height’. However, this later caused the a series of architects and housing developers to lobby the government ‘not to ban structural timber’ under the new rules.
Glenn Howells Architects, AHMM, dRMM, Waugh Thistleton and Urban Splash said they believed incuding timber in a potentially extended combustibles ban ‘is not only unnecessary on safety grounds but would badly damage the rise of mass timber construction’. Such construction is ‘seen as a crucial means of responding to the climate emergency because it could slash the building industry’s carbon emissions’.
The Architects Climate Action Network argued that timber ‘should be exempt from the ban’, urging architects to respond to the consultation, and followed the recently expressed views of Willmott Dixon chief executive officer Rick Wilmott, who warned that ‘efforts to eradicate’ combustible building materials post Grenfell risk going ‘too far’, and create ‘huge’ challenges for developers.
Inside Housing has now reported on the timber industry’s plans to spend £500,000 on fire tests over the next 18 months on cross laminated timber (CLT) to ‘prove’ its safety in housing and large building use, with the material having been ‘heralded in some quarters as the future of construction because of its low embodied carbon and the capacity to produce the panels offsite’.
With the sector concerned that government plans ‘would effectively restrict its use to low-rise projects only’, CLT’s largest three suppliers KLH, Binderholz and Stora Enso have invested in the fire tests, with the Structural Timber Association (STA) stating that the tests aim to provide a ‘harmonised testing standard’ as well as an ‘enhanced understanding of fire resistance characteristics’.
Test data would be released as it becomes available, with Inside Housing noting that CLT would be affected by any extended ban by CLT being ‘effectively’ ruled out in walls, ‘although it is possible to use the building method in the internal structure only’. It also pointed out that housing association have ‘been among the biggest users’ of the material, and some have established factories to produce the panels.
While those in support of CLT have argued its fire risk is ‘limited’, on the basis that the wooden slabs ‘char rather than burn’ on being exposed to fire, Dr Rory Hadden – lecturer in fire investigation at the University of Edinburgh – said that ‘more research needs to be done to truly understand the risks associated’ with CLT.
He stated: ‘The key thing that I would emphasise is that charring is burning. The charring process itself produces flammable gases and they contribute to the burning within a space. The timber is going to burn. It’s marketing speak to say anything else. In a non-combustible building, you have the fuel, the tables, chairs, which will burn in a way that is independent to the structure.
‘As soon as you start putting a fuel load on the walls, the ceilings, it fundamentally changes how that compartment is going to burn. [So] timber is going to require a rethink of how we do these designs.’
STA chief executive Andrew Carpenter commented: ‘The STA is… providing test-based research evidence of product performance that will enhance the understanding of fire resistance characteristics. This extensive research will be completed within 18 months and we intend to release the data as it becomes available during the testing programme.
‘Building regulations and legislation are frequently misquoted, and it is worth noting that each CLT project has a bespoke fire safety strategy relating to scheme-specific details. We’re acting responsibly to counter misinformation as there is a potential risk of taking out of the market a building material that is the most sustainable construction material.’