VikG

So after completing self build air tightness for external walls I found fairly easy to achieve unless in areas where joists were built into the wall itself. Over here we ended up using a lot of expandable foam (not the most eco friendly). One consideration that I still am unsure about (even though our build is finished) is where the internal leaf of wall meets the rafters of the roof. Since we had a warm roof this area was very difficult to make airtight. We extended the PIR behind plasterboard vertically as far as we could go (to the OSB holding the roof above but as you can imagine this created potential leaky points every 400mm where the roof rafters were. There seems to be no issue with thermal imaging, but would be nice to know if there is something else people use to seal the internal area when using an MVHR. We are currrently building the inlaws home in derbyshire and would be nice to get it right. Also when window fitters come ensure there are plenty of foam guns for them to use, they're terrible for leaving gaps all around the windows and where the cavity wall is exposed needs cavity closers.