Energy use in buildings has come more into focus in recent years. Achieving an energy efficient building is very dependent on the building’s air tightness. This can be quantified using the blower door pressurization technique. The air tightness requirements in the new and stricter Norwegian technical regulations, TEK 2007, cause considerable concern for the building industry. This leads to a growing interest for air tight constructions and methods. Air leakages in buildings have many origins, where joints around windows is one of them. This depends on the materials being chosen, sealing technique as well as the craftsmanship. This paper is a part of a PhD study, and discusses the effects on air leakages from window joints only, depending on tightening technique chosen. Measurements of 7 different sealing techniques have been carried out on a window of 1,2m x 1,2m with a continuous joint of 15 mm. The pressure chamber testing rig at SINTEF Byggforsk has been used. From the laboratory measurements it is shown that tape, wind barrier strips and backer rod contribute the most to the air tightness of the window joint. A comparison has also been made between a pulled-in and a conventional mounting of vapour barrier. The measurements show that when the vapour barrier is squeezed against the jamb liner, the pulled-in variant should be sealed in the corners to reduce air leakages. Measurements of the air tightness of a self-expanding sealing strip show that this product has the same air tightness as 50 mm mineral wool insulation.