CLT-solid wood elements are characterised by their high fire resistance
CLT solid wood elements are more fire-resistant than is generally assumed. Stora Enso CLT has a moisture content of approx. 12%. If CLT is exposed to fire and thus to an elevated supply of energy, its temperature rises and the water molecules embedded within start to evaporate at approx. 100 °C. At temperatures above 200-300 °C, these chemical compounds decompose in a process known as “pyrolysis” (whereby gas emissions from combustible components in the wood burst into flame), gradually spreading along the wood, leaving a charring area behind it. This char layer is formed from the carbonaceous residue of pyrolysis, which burns, generating embers. This layer’s properties — in particular, low density and high permeability — act as heat insulation and protect the underlying, undamaged wood. This results in a carbonised surface which protects the internal CLT layers which have not yet been exposed to fire and although in a fire, solid wood constructions become charred on the surface, the process of pyrolysis and the behaviour of wood can actually be predicted (unlike steel or concrete constructions). Through the properties of pyrolysis and the ability to form a char layer, the building material, wood, has inherited its fire resistance from nature itself. By contrast, steel constructions, for example, require additional fire protection measures. The environmentally-friendly building material offers unique features when exposed to fire, which means that CLT elements have a high level of fire resistance. To underline these statements, Stora Enso CLT has been tested by accredited institutes. The results speak for themselves, demonstrating the high level of fire resistance of CLT components. Our classification reports are available for downloading below. The results of the classification reports and a detailed description of REI criterion calculations are compactly summarised in a comprehensive document entitled “CLT documentation on fire protection” which can be found at www.clt.info/media-downloads.