Fuktsäkra parallelltak - En studie av risken för mögelpåväxt i parallelltak med variabel ångbroms

Sammanfattning: Today, it is important that the houses that are built are environment-friendly. Houses that are environmental friendly has often thick insulation and a framework in wood. To be able to do that, it is important to avoid mould growth. In this report, the risk of mould growth will be examined in a ventilated roof, situated in Lund, Stockholm, Borlänge and Luleå. The part of the roof that will be examined in this report is the roof beams. The study will examine if the risk of mould growth can be reduced with a smart vapour retarder. A smart vapour retarder absorbs the moisture in the air and opens up. The relative humidity is in general higher on the warm months. That means that the smart vapour retarder opens up in the summer, which allows the roof to dry on the inside. When the relative humidity is low on the inside, the smart vapour retarder works as a regular vapour retarder. A study of whether a typical ventilated roof will be affected of problems with mould growth in these four towns will also be done. The report will also handle the most critical parameters that are affecting the risk of mould growth. To examine this, simulations has been done in the computer program WUFI. In the simulations, one or several parameters has been varied at the same time. This is done because of the uncertainties that are in the simulations and also because that gives the information about the critical parameters. With the results of the simulations, the risk of mould growth is calculated with the MRD-model. The MRD-Model is a method to design a construction to avoid mould growth. The model is based on the critical time a material is exposed to a climate where mould can grow. The simulations show that the smart vapour retarder only can reduce the risk in cases when problems will occur anyway. The critical parameters, regarding risk of mould growth are in general: • The amount of rain that is leaking in through the roof membrane or to the Masonite board • The vapour tightness of the board, creating the air gap • The colour of the roof • The amount of air changes in the air gap • The leakage trough the vapour retarder in combination with a steam tight board. The simulations also shows that the location of the building has a big impact on the risk of mould growth. The risk is highest in Lund, lowest in Borlänge and somewhere between in Stockholm and Luleå. The effect of a parameter can vary based on the location. The original case will not be affected by mould growth in any of the examined locations. In Lund especially, the margin is small. A change of a single parameter like the amount of rain leaking in, or the colour of the roof can cause problems with mould growth.