Airtightness of timber frame buildings without a plastic film vapour barrier.

Good airtightness of a building can be achieved by the incorporation of an inner sealing layerfor the exterior walls and roofs in the form of a plastic film, which also serves as a vapourbarrier. However, if it is not wished to use plastic film as an inner sealing layer, thenairtightness must be effected through the use of other materials or in some other way. Thisproject has been concerned with investigation of a number of alternatives. It has been foundthat the arrangement most commonly used in Sweden today comprises polymer-based fibresheets (which permit diffusion) and gypsum board, as alternatives to plastic film on the insideof the structure.The work of the project has shown that, provided that the materials are airtight in their ownright, it is possible to achieve as good airtightness with alternative materials as can beachieved with plastic film. This has been demonstrated in the laboratory and in three of fivehouses in the field investigation. However, the airtightness performance of the finishedbuilding can be very poor unless care is taken both in the design and in construction, and thiswas also revealed in the field work.