Fire resistance of timber structures is an important topic of research and discussion. A popular method for protecting timber members against fire is the use of protective non-combustible claddings. For these, the most widespread material is gypsum plasterboard. A method for calculating the fire resistance of timber frame assemblies is the improved component additive method which will be introduced to the next version of the European standard EN 1995-1-2. Currently there exist formulas only for material groups. In this work two more materials are added and the implementation procedure is described. Four horizontal model scale furnace tests were conducted. Thermal simulations of the tested configurations were conducted by the finite element software SAFIR v2014a1. The thermal parameters of the studied materials were calibrated in order to obtain the same temperature rise curves as were shown in the fire tests. The calibration procedure developed was implemented on cellulose fibre insulations. With the suitable effective thermal parameters, another set of simulations was run based on the work of Vanessa Schleifer and material specific formulas derived. These were compared with results of separate full scale test results to verify the safety of the calculations.