Air seals around windows – getting it right matters

Soudal Technical Manager, Steve Loveridge discusses the importance of making sure this is done to spec – without question!

Air sealing around windows is such a fundamental task in the building and construction industry, you could imagine there was little left to be said on the topic. Unfortunately, that is not the case, as the multiple calls I receive from both contractors and architects confirms.

Done correctly, air seals will work incredibly well. Done poorly they can be a curse to the homeowner, the installer, and, in the longer term, the architect. The purpose of air seals is to provide for the equalization of air-pressure between the external and internal environments without the passage of water-loaded air. In short, the air passes, but without the water. An air seal done correctly will only extend approximately 20-25mm deep between the reveal and the framing sill and will start by having a PEF Backing Rod applied to guarantee a constancy of depth. The brilliance of expanding foam is where the real magic comes into play. The foam is applied once the PEF Backing Rod is in place, and the unbroken nature of its outer skin will allow the passage of air but importantly not moisture. It is worth noting at this point that the expanding foam should never be installed to cross the sill tape to the outside of the structure as damage may occur to this “outer skin” which then gives rise to further potential for moisture uptake into the building. The best air-seals will be capable of moving with the building structure and this is what a correctly applied system of PEF Backing Rod and Expanding Foam will guarantee. In this regard Soudal Gorilla are proud to be the New Zealand market leader in bespoke foam products for these purposes with Gorilla Pro Expanding Foam and Gorilla Flexi Expanding Foam at the top of the specification list.

For more information on air seals or technical advice on sealants, foams and adhesives, please contact our technical team on 0800 70 10 80 or visit our website to see our comprehensive product range and technical data www.soudal.co.nz/products/

This Tech Tip was supplied by NZCB National Partner Soudal. Soudal are a key supplier of sealants, foams and adhesives to tradies under our iconic Gorilla brand. For over 30 years Gorilla Grip, Foam, Glues and Silicones have proven their quality, reliability and technical performance in kiwi conditions. www.soudal.co.nz