Wood-based materials, including wood-based building products and components, have a predictable and controllable fire behaviour in the design of buildings, in particular based on the application of regulated national and European design methods. This explains its current widespread use, and why wood-based materials are recommended in the construction of all types of structures.
The fire stability
The fire stability of timber supports and structures is achieved by limiting the temperature rise of the timber.
The fire protection of timber cannot be applied directly to the timber and must be accompanied by the installation of an expanded metal sheet.
The protection consists in Nergalto NG1 or equivalent sheets laid perpendicular to the beams (the sheets are laid side by side with an overlap of 100 mm) combined with the application of a fibrous, fire-retardant coating designed for fire protection.
The methods for predicting
The methods for predicting the fire behaviour of timber structures by calculation are described in Eurocode NF EN 1995-1-2. DTU 88 stipulates that timber components must resist fire at a rate of 0.7mm per side and per minute within a minimum time of 1/2 hour for buildings.
In the presence of timber structures designed to achieve a given fire resistance rating within a given period, the weak points are the metal elements. The heat can deform metal elements and impact on overall stability. Metal elements therefore have to be buried in the timber in order to protect them.
The burn rate of timber elements depends on which tree species are used (softwood, hardwood), the thickness of the elements, the moisture content and exposure to the fire. The burn rate is inversely proportional to the density and mass (section/perimeter) of the timber elements. Large blocks (over 6 cm thick) burn slowly. The outer layer of charcoal slows down combustion (the thermal conductivity of charcoal is 1/8 that of solid timber). Solid timber or glued laminated wood burns at a rate of 1 cm per side per quarter hour and planks at 1.5 cm per side per quarter hour.
Projiso manufactures and markets a wide range of spray-on fibrous coatings, such as Fibrofeu® or Firespray®, designed for fire protection of timber structures.
The product will be chosen according to the various issues specific to the site.