Fire retardants may considerably improve the reaction to fire properties of wood products, but the long term durability needs to be addressed. Several long term studies of fire retardant treated (FRT) wood products over time are presented. They are performed according to a European system based on earlier Nordic and North American systems and include accelerated aging according to different procedures and natural weathering up to 10 years.

Main conclusions are:

• The hygroscopic properties are unchanged compared to untreated wood products for most FRT wood products studied and used commercially

• The reaction to fire properties of FRT wood may be maintained after accelerated and natural aging if the The hygroscopic properties are unchanged compared to untreated wood for most FRT wood retention levels are high enough, but several products lose most of their improved reaction to fire properties during weathering

• Paint systems contribute considerably to weather protection and are usually needed to maintain the reaction to fire performance at exterior applications