In this paper, the authors made attempt to analyse the influence of moisture in the external wall of a building on the distribution of the temperature field, using numerical and experimental methods. Studies were carried out in the places of heat leakage occurring in structural joints of a single-family residential building, built in the traditional technology. In this study, the thermal bridge parameters were calculated by determining the values of thermal and moisture identifiers. For this purpose, two three-dimensional models of the building partition were designed based on an existing structure, and the boundary conditions for simulations were determined. The obtained heat flux values made it possible to perform quantitative calculations of heat flux distributions and temperatures of construction joints within the thermal bridge occurrence area. Moreover, the accuracy of the final temperatures obtained after combining the mathematical models with the values determined from thermograms was evaluated. In order to validate the results of numerical simulation, a test model was used taking into account the parameters specified in PL-EN 15026. The analysis aimed to present the handiness of using the simulation at the stage of planning the design and thermomodernisation of buildings in the places particularly exposed to adverse terrain and atmospheric conditions.