insulation #2
Busy, busy, busy insulating!
This past month has seen a variety of areas of our house build progressing, with a mixture of tasks including more external wall insulation, over-insulating the window frames, and the installing of some glulam post balustrading / support for our stair!
We have now almost completed the 3-layered external wall insulation and the Spano Durelis Vapour Block internal airtight racking, with only a corner of the double height space still to go. The photos below show some the master bedroom in progress...
After the 60mm layer has been completed... After the 160mm inner most layer has been completed... Finally, after the Spano Durelis board has been fitted.
Although this task has been ongoing for a while now we are still amazed at how pleasant the wood fibre insulation is to work with, with no itching or inhalation issues when cutting it. We have deliberately broken up the monotony of undertaking this task over the whole building with other jobs, so although on the one had it feels like we have been doing it for ages and are now 'old hands', we have really only spent a few weeks in total on it!
The other job we have been doing along side this is the over-insulating of the outside of the window frames. This is a really important detail in terms of reducing or eliminating thermal bridging at the window frame edge, with the recommendation for a typical overlap onto the frame of between 30-40mm, or more, depending on the frame dimensions;
In the first photo below you can see the main line of the 100mm thick Gutex on the left, with a second 100mm thick piece inserted afterwards between the first layer and the window frame. With hindsight I would detail this junction slightly differently however we had some sequencing issues on site which slightly forced our hand to insert a second piece of insulation after the main outer layer was completed.
These photos show the additional layer of insulation being inserted up one side of the window frame...
The second photo above shows the 30mm overlap onto the frame (note the front piece of insulation here will need trimmed back with a jigsaw to match the piece immediately adjacent to the window frame as it has accidentally been extended too far beyond the line of the window frame, which is another slight snag in the sequence we have chosen)...
The third shows a (small) 15mm space at the side of the projecting section of aluminium window frame for taping onto!
As we are not using certified units the frames aren't as long (or wide) as they might be which means that we are a little limited as to how much insulation we can actually overlap the frames with. During the design phase we were aiming for 30mm maximum and in reality we have achieved this, however due to the slight projection of the aluminium section of the outer part of the window frame it doesn't leave much room at the window frame edge for our wind-tightness taping detail. Whilst we still think this will be achievable for us (or me with small fingers!! as we did a little test before finally fitting the insulation) it has shown us that this detail needs some careful consideration on future projects to make sure that it can meet all of the requirements of a well insulated yet wind-tight frame-to-insulation junction in as straightforward a manner as possible.
We still have to fit a small tapering piece of insulation under the cill...
Initially our detail here was to simply tape any joins in the external Gutex insulation that are not tongued and grooved as it is this that keeps the joins wind-tight, however we have since decided that it would be quicker and more robust to simply use a wind-tight membrane all around the reveals which is taped to the window frame and out onto the front face of the Gutex. This will then cover all of the various joins around the windows (tongue & grooved or not) and leave us in no doubt that we have achieved a good wind-tight detail at each opening. We are planning to use Pro Clima's Fronta Quatro membrane with black Tescon Invis tape, for both performance and aesthetic reasons.
As we are going to bring the open rainscreen larch cladding into the window reveals as we want to make sure that all of the tapes and so on used here are black so that they are not visible behind the gaps in the cladding.
We will be working more on this detail over the next few weeks, but it has certainly been one of the most interesting to execute so far!