As we know, the measure of fire resistance (FR) is the time elapsed from the start of the fire until the point where the material fails to function. CLT’s fire resistance comes in the form of ‘charring’. When the timber is exposed to a fire that burns to a temperature in excess of 400 degrees C, the surface of the timber ignites and burns at a consistent rate. As it burns, it forms a black layer of ‘char’. This char is an insulating layer that prevents an excessive rise in temperature inside the core or ‘unburnt’ part of the panel. This core maintains its structure and continues to function for the period of fire resistance.

While the debate continues around the efficacy of the testing, CLT panels can be produced with an FR of 30, 60 and 90 minutes, so it is a certified fire-safe material. However, it isn’t as simple as just rating the CLT. If you have a project coming up that features CLT, you really need to consider where and how services will be penetrating, and if there are any FR requirements for the structural steel supporting the panels. These elements need to be protected collectively for the FR to be achieved.