Moisture safety in wood frame walls : blind evaluation of the hygrothermal calculation tool WUFI 5.0 using field measurements and determination of factors affecting the moisture safety

Sammanfattning: Due to increased awareness of climate change and higher energy costs, well‐insulated buildings have become more common. Furthermore, the interests of using wood in building to produce more carbon dioxide‐efficient houses have increased. However, thicker thermal insulation in walls increases the risk of high relative humidity levels and the risk of mould‐related damage in Wood frame houses. In order to predict moisture damage it is important to have a properly verified, userfriendly and reliable calculation tool that can be used in the design phase. The first part of the thesis presents a blind method that can be used in order to verify heat and moisture calculation tools in a reliable manner. General results and findings from blind validations using a one‐dimensional transient heat and moisture calculation tool are summarized and presented. The comparisons include measurements and calculations of temperature and relative humidity and were carried out in Northern European climates. The thesis also presents important factors affecting the risk of mould growth in well‐insulated Wood frame walls. A parametric study is presented in which moisture‐critical positions in traditional Swedish wood frame designs in Northern European climates are investigated by using hygrothermal modeling. Traditional Swedish walls with insulation thicknesses of 220 mm are then compared to walls with thicker thermal insulation and alternative designs. In general the comparisons of measured and blindly calculated values show a good correlation. The results show that the studied tool can be used during the design phase to predict moisture risks. However, factors such as the influence of impaired temperature affecting the calculated RH have to be taken into account. There is also a need for developing outdoor climate boundary conditions that take into account critical periods and variations between different years. It has been found that there is a higher risk of moisture‐related damage in thicker insulated walls. However, this risk can be reduced by choosing more suitable designs in which well‐ventilated air gaps behind the claddings and exterior vapour‐permeable moisture proof thermal insulation boards are of great importance.