airtightness
Making the window reveals airtight.
This week we also began the process of making the window and door reveals airtight! We did the window which is right next to the MVHR cupboard first as we needed to complete the wall build-up before the Paul unit was fixed to the external wall.
As this was the first window I did I tried a few different methods / sequencing of the various layers in order to see what was most effective, quickest and used the least tape! Below is a step by step of the key stages...
The first step was to staple the membrane in place that bridges the airtightness 'gap' between the window frame and the Spano Durelis wall board. I began by pressing it into the corner (so that when we fill the service cavity zone that wraps into the window reveal the insulation can fit snugly against the window frame) and stapling it roughly in place a few times. Once it was in place all down the window reveal I went back and stapled it at 100mm intervals in each direction. I also stapled it onto the window frame itself so that we are not relying solely on the adhesion of the tape to the frame to hold it in place.
In these two photos you can see that I have stuck the first piece of Pro Clima Tescon Profil tape to the window frame without the membrane in place - after this window I decided it was simpler, and a fractionally more efficient use of tape, to have all of the membrane in place all round the window first, then do all of the taping in one go.
The Profil tape is really handy for this type of application as it has 2 release papers which means that it can be adhered to one surface first and then smoothed onto the second surface without creating wrinkles etc.
I overlapped the membrane slightly up over the adjacent side of the reveal (so in this instance top and bottom) to avoid having a taped join right in the corner - in later windows I moved this overlap further away from the corner.
As you can see here on this window I stapled and taped each side before moving on to the next as described above. You can also see there is a corner of membrane 'missing' at the external face of the window reveal due to the relief cut made as the membrane wrapped up around the corner.
The second photo shows the tape over the join between the two strips of membrane, but right along the internal corner. With more experience at taping this was less difficult to execute, but I still decided to move this junction to a flat area for ease. Again on this window I made a relief cut in the tape at the external corner.
I then taped over this relief cut to complete the airtight layer here... Then I taped a small section vertically between the two pieces of membrane... Then I made an internal 'corner', which Steven from Ecological Building Systems showed us how to make on his recent visit. This is basically a square of tape with a slot cut in one side, which allows a 3-D internal corner to be formed. The next photo shows the 'corner' stuck in place... Finally, above are a few shots of the finished window.. We also used Pro Clima Tescon Vana tape, which has a single release strip, to adhere the membrane to the Spano Durelis board around the perimeter of the opening.
In this last photo we have started to add the service cavity battens, which are screwed through the Spano board into the structure behind. We then filled between them with Steico Flex wood fibre insulation before sheeting the wall.