Capturing the impact of wind driven rain on solid-brick wall dwellings

Approximately 6.5 of the 25.3 million dwellings in the UK having solid-brick walls, insulating these dwellings could have a substantial impact on reducing energy usage. Applying internal wall insulation could, however, have a negative impact on the moisture risk for the inhabitants. The research in this PhD thesis evaluated the impact of the risk of wind driven rain to the moisture-safe insulation in solid-brick dwellings across the UK by (1) identifying the predominant factors impacting the moisture risk for solid-brick walls for various UK weather locations, (2) measuring the response of solid-brick walls to different wind driven rain events under dynamic boundary conditions and (3) evaluating the long-term moisture risk from wind driven rain when insulating solid-brick dwellings.

Throughout this research project four wall structures were examined: an uninsulated baseline lime mortar wall, an insulated wall with a vapour tight insulation (EPS), an insulated wall with a vapour open insulation (mineral wool and a vapour barrier) and a lime mortar wall structure with a hydrophobic layer at the exterior side of the wall.

To identify the predominant factors impacting the moisture risk for solid-brick walls for various UK weather locations an uncertainty and sensitivity analysis was executed. The results of this analysis have shown that parameters affecting the dimensions and thermal characteristics of the wall structure had the largest influences on the hygrothermal behaviour of the wall structures.

The response of solid-brick walls to different wind driven rain events under dynamic boundary conditions was evaluated during laboratory experiments. From the data collected, it was concluded that the response of the wall structures was different under the two different ways of applying wind driven rain to the wall structures. In contrast to intermittent rain, continuous rain water could penetrate the complete wall and thus lower the thermal resistance of the complete wall rapidly. Furthermore, it was concluded that moisture stayed in the wall longer than expected.

Evaluating the long-term moisture risk from wind driven rain when insulating solid-brick dwellings was performed with numerical simulations. The simulated ten-year periods of current and future weather for different wall structures on two locations, with low and high wind driven rain, showed that the moisture risk was high for all wall structures and for both locations. The performance of the wall structures in the future weather scenarios was found to be very dependent on changes in the external relative humidity.

The main implication of the research is that the application of interior wall insulation on solid-brick wall dwellings will increase the risk of moisture problems and thus be detrimental to the health of the inhabitants of the dwellings. This means that large-scale insulation of these dwellings is not possible. When retro-fitting individual solid-brick wall dwellings, a cautious approach is needed with simulations of (un)insulated, especially concerning the applicable weather.