ᐅ Insulate the cavity between the window and the wall structure!

Good morning,

to get straight to the point, what is the best way and material to insulate the cavity? I have looked into external thermal insulation composite system (ETICS) panels or stuffing in Styrodur panels and then foaming? I had an argument with the window installer because I disagreed, and now I’m faced with the problem and would like to fix it myself if possible. The window installer only applied foam underneath and said that would be sufficient… He said: use mineral wool and pack it tightly until it’s sealed, but I definitely didn’t want to accept that solution…

Best regards
goubilas

This needs to be airtight. Using expanding foam is nonsense. In general, what I see in the picture is just poor workmanship.

In my opinion, it should be properly filled with masonry and then sealed carefully.

We are building with 36.5cm (14.4 inches) Poroton clay blocks filled with mineral wool. Cutting these blocks is not easy because they break very quickly. I also considered filling the cavity with mortar strips—would it be possible to fill the entire cavity with these strips to make it completely airtight? They are easy to cut. That’s what I had in mind, but I wanted to ask what you think about it.

You can also fill the gap with regular unfilled perforated bricks or even better, Ytong.

With Ytong, you have the advantage that the block has no hollow chambers and is easy to cut.

For sealing, use mounting foam and compression tape. That’s how I would do it.

What speaks against filling the gap with perimeter insulation strips (extruded polystyrene boards)?
I bring this up because I still have plenty stored. In addition, foam seal every small opening and apply compressible sealing tape below the window.

Basically nothing. Maybe the very poor sound insulation? To me, it seems somewhat unstable, even though I have often used extruded polystyrene (XPS).