Air Seal Tapes

Around 10% of heat loss is via uncontrolled ventilation, or gaps and cracks. This equates to £400 for a typical home. Windows and doors are particularly problematic, especially on older cavity walled properties that lack cavity closers or where windows are installed poorly into uneven openings.

Window installers will default to expanding foam which can be good for filling unwanted voids, but it is not an airtight solution. Air seal tape should be used, linking the frame back to the internal airtight layer (typically on the inside) like a wet plaster layer or sheathing board.

If you’re a customer: ask for cavity closers to be fitted to cavity wall openings when windows are replaced and insist on air seal tape around the whole assembly for a proper airtight seal.

For designers and specifiers: clearly identify the airtightness layers on all details and specify air seal tapes for best practice window installations. Communicate to the installer the need for cavity closers to be fitted using Approved Document Part L1 10.3c along with a requirement for photographic evidence for Building Regulations compliance.