Measuring and mitigating overheating risk in solid wall dwellings retrofitted with internal wall insulation

Upgrading the thermal insulation of UK houses to improve wintertime energy efficiency raises concerns about potential summertime overheating risk. To address these concerns, experiments were conducted in a pair of thermally matched, solid walled houses, located in the UK. One of the pair was retrofitted with internal wall insulation, while the other remained uninsulated; both houses were monitored for four weeks during the summer of 2015. Operative temperatures in the living room and main bedroom were observed to be higher in the internally insulated house in comparison to the uninsulated house. The houses were again monitored for a further three weeks with a simple overheating mitigation strategy applied consisting of night ventilation and shading using internal blinds. The data were normalised for variations in external weather conditions using a linear regression model, with the exponentially-weighted outdoor running mean air temperature as the predictor variable of indoor operative temperature. The results showed that the mitigation strategy was effective at reducing the internal temperature in the internally insulated house to a level similar to that observed in the uninsulated house. The marginal increase in overheating risk should not be considered a barrier to the uptake of IWI in this type of house and location, at this time. Shading devices and secure noise attenuating vents for existing dwellings may be needed as part of a package of refurbishment in the future. It could become a requirement within the Building Regulations [1] to reduce overheating risk when retrofitting existing homes.