Fire retardant treatments (FRT) may considerably improve the reaction to fire properties of wood-based products and the highest fire classifications for combustible products can be reached, but the maintained reaction to fire performance e. g. in exterior applications needs to be addressed in order to form a basis for new and reliable wood products with improved fire performance. A European Technical Specification with Durability of Reaction to Fire performance (DRF) classes has been developed in order to assist product development and to guide potential users to find suitable FRT wood products. It is based on ASTM standards and has been further developed upon Nordic initiatives from industry and research as Nordtest methods. It consists of a classification system for the fire properties over time of FRT wood and test procedures for hygroscopicity and accelerated weathering covering both interior and exterior applications. The European system has been applied to a range of commercial FRT wood products and products under development and a long term experimental study on the maintained reaction to fire performance of FRT wood products over time has been performed. It includes accelerated ageing according to different procedures and natural weathering up to ten years. Main conclusions are: - The hygroscopic properties are unchanged compared to untreated wood for most commercial FRT wood products - The reaction to fire properties of FRT wood may be maintained after accelerated and natural ageing if the retention levels are high enough - Several FRT wood products loose most of the improved reaction to fire properties during weathering - Paint systems contribute considerably to maintain of the fire performance at exterior application The results of the long term study show that requirements for interior applications of FRT wood products often are fulfilled, while products for exterior applications with maintained fire performance over time are rare. There is thus a strong need for product development for exterior applications. In the meantime, requirements on the long term durability of the fire performance of FRT wood products should be included in the national building regulations. There is also a need to determine the relationship between accelerated and natural weathering in different climates in order to further develop the conditions for accelerated weathering.

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