By Minnie Ashdown
According to the International Energy Agency, making buildings airtight may reduce building heating loads by 20-30%. Given that space heating accounts for approximately 48% of UK energy consumption by end use (from DUKES 2018), there’s good reason for builders to focus on making buildings more airtight.
This role played by unplanned air leakage on heating and cooling energy costs, as well as buildings energy efficiency, makes it vital that builders meet targets for building airtightness. These targets form part of an overall energy rating for a building, that all new buildings must attain in order to be considered complete.
A new publication from Lolo student Minnie Ashdown has shed light on the improvements in airtightness achieved in new dwellings, around the time that new guidance was released to builders. While limited by a relatively small dataset, the research suggests that although developers were able to meet more stringent design targets, they were not always able to meet them through improvements to the primary air barrier (boundary between the indoor conditioned space and outdoor unconditioned space), rather, last minute alterations to the building were made in order to meet targets.
While the alterations did have the effect of meeting the airtightness targets, in around 20% of cases, measures such as foam, tape, or mastic sealant are likely to have been used, which might not have the same longevity as improvements to the primary air barrier. If these measures don’t last as long as the rest of the building fabric, the energy efficiency of the building will deteriorate faster than it otherwise might. This could be the case if, for example, mastic is used to seal a gap between the floor and the wall, which is then removed to fit a carpet. This suggests that developers need better guidance in meeting airtightness targets, and that there may be a role for incentives and support that can generate more robust shifts in building practices in order to deliver more airtight buildings.
Further, it was shown that small aggregate differences between airtightness distributions of construction techniques exist, which implies that some construction methods perform better than others in terms of airtightness. Minnie says “The most airtight construction methods in the dataset were reinforced concrete frame and dry lined masonry, followed by timber frame and light-weight steel frame. This is good news for dry lined masonry, because it’s sometimes associated with a lack of airtightness.”
If the UK is to meet its 2050 commitment of net zero CO2 emissions, it is necessary that new buildings are built to standards that can minimise unwanted heat losses, and buildings that can maintain standards as they age are essential. It will also be vital to understand the causes of differences in airtightness between building methods, and how practices can be improved to deliver a more airtight primary air barrier, to support developers in achieving highly performing buildings.