In an experimental study the effect of fire protection of gypsum plasterboards attached to timber frame wall or floor assemblies was investigated. The principles of standard testing to be introduced in the CEN prestandard ENV YYY5-5 is presented, based on temperature measurements on the surface of the timber member and inside of it. For non-load bearing walls, a component additive method for calculating the total fire resistance has been developed and experimentally verified. This method has also achieved technical approval from the Swedish building authorities.