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A method for the determination of the effective constant coefficients of the transverse coupled hygrothermal diffusion is presented. Onsager’s reciprocal relation [2] is utilized to reduce the number of the diffusivity coefficients of constitutive materials from four to two. The so called cross coupling diffusivities are expressed in terms of the thermal conductivity and the coefficient of diffusion. The representative volume element of the composite is analyzed by applying a twodimensional finite element model. It is assumed that the composite is undamaged, and there is no resistance in diffusion and heat conduction at the interface of the fiber and the matrix. The method is tested numerically with a set of different cases. The coupling affects most clearly to the heat flux in the tests. The average coupled heat flux is significantly greater than the uncoupled heat flux.

The present paper deals with a study of different climate effects and defining boundary conditions on mould growth risk inside building envelope. The case structure represents a common envelope of timber-framed singlefamily house. Weather conditions from Utsjoki, Oulu and Joensuu are considered in the analysis representing climate gradients wet and dry, coastal and inland conditions during a period of 6 years.Mould growth initiation and progression require a sufficiently high humidity at suitable temperature range. Coastal regions characteristically have humid and warm climate that causes higher risk for mould growth than the more dry inland locations. The most unfavorable conditions for mould growth were seen in the coldest and the northernmost location. Hygro-thermal simulation also presented significant differences in key interior boundary conditions that, considering standard approach, may be interpreted as potential structural health issues.