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HAVÍŘOVá, Z., KUBŮ, P.: Reliability and service life of wood structures and buildings. Acta univ. agric. et silvic. Mendel. Brun., 2005, LIII, No. 5, pp. 39–52 Service life of constructions and buildings of wood is dependent on temperature and moisture conditions in layers of the building cladding where the wood framework is built in. Temperature/moisture conditions or the corresponding equilibrium moisture content (EMC) of the construction show considerable effects on the functional reliability of the whole building from the viewpoint of mechanical resistance and stability (ER1), energy savings and thermal protection (ER6) and hygiene, health and environment protection (ER3). To ensure the reliability of constructions and buildings for the period of their supposed service life a more profound analysis of constructions is necessary from the aspect of a global thermal/technical evaluation. wood, construction, moisture, deformation, creeping, reliability Ročník LIII 5 Číslo 5, 2005 39 During last years, a marked shift occurs in the design and realization of buildings as low-energy constructions, ie buildings with the low consumption of energies for their operation and heating and towards the development of corresponding constructions of cladding. The development is particularly aimed at increasing the thermal resistance of the cladding or decreasing its coefficient of heat passage above all by means of increasing the thickness of a heat-insulation layer. Moreover, the maximum reduction occurs of heat losses by air infiltration through constructions and their joints. Methods of the design and realization of buildings and constructions of wood are also subject to these global trends. However, an endeavour to reach as low as possible heat losses in buildings of wood through decreasing the coefficient of heat passage in cladding constructions and through decreasing or elimination their air infiltration must not affect other fundamental requirements posed on these constructions and buildings. Simultaneously with the above-mentioned trend in energy savings and heat protection the designer and constructor have to see that mechanical properties and stability of constructions and buildings not to be worsened and hygiene and health protection of users of these buildings to be ensured. In increasing one of the properties referring to basic requirements the functional reliability of the constructions and buildings must not be limited or reduced from the viewpoint of other basic requirements and the adequate service life and durability have to be guaranteed. This requirement is also included in ETAG 007 Operating instructions for European technical approvals – Wooden frame structural configurations, article 4.7.1 Viewpoints of durability. MATERIAL AND METHODS We shall concentrate on interrelations of three basic functional requirements which are most important for designing and realization of wooden frame constructions: mechanical resistance and stability (ER1), energy savings and heat protection (ER6) and hygiene, health and environment protection (ER3). In addition to instant returnable deformations time-depen40 Z. Havířová, P. Kubů dent partly irreversible deformations also occur in wooden constructions which are induced by the effect of a long-term load (Cai et. al., 2002). In a European standard for designing wooden constructions (EUROCIDE 5) as well as in a corresponding Czech standard the problem of creeping is dealt with by means of the coefficient of creeping kdef (Tab. I) which is dependent on the period of loading and the environment moisture. The European standard establishes 5 categories of load: constant, long-term, medium-term, short-term, instant and 3 classes of use: class1 (protected interior) , class 2 (interior with the occasional occurrence of moisture) and class 3 (corresponds to an unprotected exposure). The element deformation in the course of time is expressed by a relation: ufin = uinst (1 + kdef), (1) where uinst expresses an instant deformation, ufin expresses deformation including creeping after the certain period of load. I: Values of the coefficient of kdef for solid and glued laminated wood according to(EuROCODE ) Class of the period of load Class of use