Features: York House
Watch Architecture Today's webinar which explores fire safety in timber buildings and hear associate Anna Beckett's thoughts on the topic.
Mass timber is an immensely attractive material, aesthetically and environmentally, and also because of its lightweight properties. But barriers to its use are becoming greater, due largely to worries about its behaviour in fire. This is coming from two main directions – from changes to the Building Regulations, and from increasing concerns by the insurance industry. This webinar examined the issues and suggested some ways forward.
As Anna Beckett of engineer Webb Yates said, ‘Timber doesn’t burn as you would expect it to. The perception doesn’t agree with the way that it actually behaves.’ The fact that timber is not as flammable as some fear, and that it is usually protected from burning through by a char layer, does not mean that there are no problems.
Beckett explained how regulatory changes make it necessary to adapt designs. She showed some of the projects that the practice has worked on previously and discussed how they would have to change if built today.
For example, at York House in London’s King’s Cross, designed with architect dMFK, the front and roof extensions are in CLT and glulam. The CLT was sized to allow for the thickness lost to charring. At the time – 2019 – this was considered adequate and the CLT could all be left exposed. Today, Beckett said, the fire treatment would be different.
On a project at Old Street with Mary Duggan Architects, the team is looking at a hybrid steel and concrete structure. They were advised that either the ceiling or the walls of the CLT elements needed to be covered, because of concern about a build-up of heat in the joints.
Beckett provided several considerations for the design of future timber buildings:
• Choose a fire engineer and building control who have experience and are familiar with timber buildings.
• Have conversations about fire design early in the design process
• Full-scale testing or modelling for fire is likely to required
• It is unlikely both the walls and ceiling can be exposed
• Consider the charring depth for solid timber and charring with delamination for CLT.
• Sprinklers may be required even in low-rise buildings.