Moisture safe cold attics - Assessment based on risk analyses of performance and cost

Paper in proceeding, 2014

Problems with high humidity levels and mould growth in cold attics have been increasing over the last few years. A recent Swedish study showed that as many as up to 60 – 80 % of the single-family houses in Västra Götaland (largely, the Gothenburg region) are showing significant mould growth and thereby risk developing serious moisture problems. The high humidity levels are to a large extent a consequence of the increasing demand on energy efficiency. Houses are frequently retrofitted with additional attic insulation, which leads to a colder attic space and hence a higher humidity. Furthermore, furnace heating is often replaced in favour of heat pumps or district heat. This may alter the air-pressure balance of the house, resulting in an increased thermal pressure on the ceiling with subsequent air-leakage up to the attic. Also newly built attics have problems. A risk assessment of the risk for mould growth is performed for different design of the attic. Also a simplified life cycle cost is estimated for the different design alternatives. The alternative with controlled ventilation is estimated to be risk free with lowest life cycle cost. Roof insulation gives low risk for mould growth in northern part of Sweden.