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Poor airtightness in buildings can lead to an over-consumption of energy and to many issues such as moisture damage and poor indoor climate. The timber frame constructions are particularly subject to air leakages, and further knowledge in this field is needed to meet the regulation requirements tightened by the development of low-energy and passive houses. This article focuses on a three-scale experimental study carried out in laboratories to quantify the impact of a number of construction details on timber frame wall airtightness. For this purpose, we built two original experimental setups and to complement an existing large-scale facility. Each setup enables to carry out pressurization tests at a different scale. The results put all together give quantitative information for more accurate simulations of building performance. Some specific construction details were investigated. It has been found in particular that the density of the insulation material is significant since a soft glass wool can have an air permeability three times higher than a rigid one with the same thermal performances. Moreover, it has been pointed out that the bond between the gypsum board and the insulation has a significant impact on the resulting pressure–flow law, and to ensure that there is no air gap the whole interface should be glued. The air flow directions also influence the flow values for high-pressure differences. Finally, at wall scale we have found that the sealing of the gypsum boards and the vapor barrier against the bottom wall plate is not very significant as long as the exterior side is sealed correctly. On the other hand, a proper sealing on both sides of a window is required because of the air gaps along it. [ABSTRACT FROM AUTHOR]