Research done in North America, where there is a significant proportion of timber frame houses, confirms that fire safety in a house or flat has little to do with the combustibility of the structural materials used. Occupant safety is far more dependent on the occupant’s awareness of fire hazards, the contents of the home and fire protection measures taken during the building’s construction.
How fire codes work
Fire codes are building standards designed to maximise occupant safety. The main objectives of fire protection codes are:
- to confine the fire to the area of its origin
- to ensure structural integrity of the building is maintained during evacuation
- to ensure measures are in place to allow for the safe exit of occupants
How construction materials are fire-rated
Complete wall assemblies are subjected to fire, then timed to see how long they maintain their integrity. Fire ratings are usually expressed as times. So a “30 minute fire rated” wall is less fire resistant than a “60 minute fire rated” wall. It is important to note that individual components are not tested, but complete assemblies.
Fire damage to various materials
No material is completely fire proof. At TRADA [Timber Research and Development Association] & Canadian National Research Councils, studies were undertaken on how various materials react during a fire. Steel will soften at high temperatures, and it will lose its structural integrity. Concrete and brick are prone to “explosive spalling,” which means moisture in the pores of the material suddenly boils and “explodes” mortar or concrete. Timber maintains its structural integrity surprisingly well. Once the exterior of the timber has charred, the fire has no fuel left, and simply goes out, leaving the centre of the timber untouched.
Closed panel systems
Even during construction, closed panel systems are very difficult to burn. This is because a fireproof layer, in the form of gypsum board (also called wallboard or plasterboard) is installed at the factory. This highly fire-resistant material forms a coating to protect the panel. When gypsum board is exposed to fire, the release of moisture from the gypsum cools the fire. Specially manufactured fire resistant rated gypsum board is available.
Off gassing and insulation
How much insulation in the wall cavity of a timber frame wall panel off gasses during a fire depends on the insulation material. Urethane foams melt quickly and can give off noxious gasses, fiberglass is difficult to ignite, but melts quickly once it does, and emits formaldehyde gas. Blown cellulose is generally treated with fire proofing chemicals at the manufacturing stage and does not burn well. Rock wool simply shrinks and also forms added protection to wood joists.