Air tightness is particularly important to achieve buildings with low energy demand. The air tightness requirements in the new and stricter Norwegian technical regulations, TEK 2007, cause considerable concern for the building industry. Thus there is a growing interest of forecasting whole buildings’ air tightness based on sealing techniques chosen. In the paper “Air tightness performance of different jointing methods for windows in wood-frame buildings”, the air tightness of different sealing techniques for window joints were measured and discussed. This paper represents a continuance of the same PhD study, and focuses on the resulting n50 air change rate, depending on window joint sealing method chosen. Different wood-frame buildings of gross area around 150-200 m2 with various numbers of windows and geometries have been analysed. This gives a basis for calculating the contribution of air leakages from the windows to the buildings total air change rate. Calculations show that the geometry of the windows is of the utmost importance to the total length of window joints. In turn this is essential to the total air leakage contribution from windows. Architects designing energy efficient buildings therefore should deliberate while planning the number and geometries of windows. This will take both the potential of air leakages and thermal bridges into account.