In this graduation thesis the calculation of standard fire resistance of a simple single span timber beam is presented. The calculation is executed in accordance with EN 1995-1-2:2005 – Eurocode 5: Design of timber structures – Part 1-2: General - Structural fire design. Standard gives two simplified methods for determining fire resistance, the thesis is focused on reduced cross section method. Fire resistance is determined for floor beams with constant cross-section, made from solid timber and from glued laminated timber, and also for glued laminated timber roof beam with variable cross-section. Design of beams for ultimate and serviceability limit state is also executed in accordance with EN 1995-1-1:2005 – Design of timber structures – Part 1-1: General - Common rules and rules for buildings. On the basis of presented study it can be concluded that the fire resistance of timber beams is relatively high (> R60) which is a consequence of serviceability limit state being relevant for the ambient design of the beams.