Future Risks on Moisture Safety in Ventilated Parallel Roofs: A Numerical Study of a Common Roof Type in Sweden Subjected to Future Weather Data Sets

Abstract

The climate is changing. The prognoses are a higher outdoor temperature and an increased absolute vapour content in outdoor air for all of Sweden. In Sweden today many roofs are already subjected to moisture-related damages and the guidelines for moisture safe design roofs are sparse. Two different roof constructions are normally used in Sweden today: the attic and the ventilated parallel roof. The ventilated parallel roof has not been evaluated for a future climate. The purpose of this study is to investigate the moisture safety of ventilated parallel roofs subjected to a data set of future climates. The effect of orientation, inclination, colour and additional exterior insulation is evaluated for different locations in Sweden. Parallel roofs in Sweden are often ventilated by natural driving forces: wind and thermal buoyance. The model of the study considers a full data set of meteorological data for calculating directional dependent thermal buoyance, moisture infiltration from indoor to outdoor due to pressure differences, and moisture and heat transport through the roof. The result shows a future increased risk of mould growth in ventilated parallel roofs in all of Sweden. North is the dimensioning orientation. The most efficient way of reducing the risk is to use a reflective and bright-coloured roof.