Timberbond Glulam timber burns slowly and resists heat penetration by the formation of self insulating char. When large glulam members are subjected to fire, the uncharred inner portion maintains its strength, giving the structure a higher survival factor.

The Fire Rating Design of timber structure is particularly well developed in New Zealand where The Code of Practice of Timber Design NZS 3603:1993 Section 9, sets out clearly methods of calculating the fire resistance of load bearing structural timber members. In calculation of the fire resistance rating of glue laminated timber elements it is assumed that charring of exposed surfaces of the Glulam member occurs at a uniform rate, and, in the case of NZ Radiata Pine, it is taken as 0.65mm per minute.

When exposed to heat of a fire, timber undergoes a thermal breakdown (pyrolysis) into combustible gases, and a layer of charcoal forms on the burning surface.

Effects of fire testing on Glulam Timber

A) Original size
B) Section of a member after a half an hour of fire testing
C) One hour of fire testing

The rate of progress of pyrolysis is governed by the low thermal conductivity of the timber and the lower conductivity of the charred layer, which also hinders the access of oxygen to the timber surface. The total insulating effect of the char and timber is such that temperatures only a short distance in from the char line will not rise sufficiently to impair the strength of the wood.

An experienced structural engineer should design fire resistance of timber structure or contact Timberbond for assistance. Other fire protection such as use of fire retardant chemicals to reduce flaming by raising the temperature of ignition and retarding spread of flame are available to meet client's design requirements