Build window reveal with insulation boards

So what is it, basement or ground floor?
The basement may be made of pumice, but above it is supposedly a 1975 Neckermann, hence from Streif, which is not made of pumice (?)

Without a lintel very risky. Absolutely do not do it.

So put in a lintel, take out the window opening. Then plaster the wall evenly. Install the window. Do not use foam sealant. The opening should be about 2-3 cm larger all around than the actual window. Compression tape goes between the wall and the window. No foam sealant.
Inside and outside, the window should be sealed with breathable window sealing tape. Then stick the Styrodur on, 3 cm thick, on both inside and outside. On that, stick the window connection tape and plaster the window.

That is how a proper RAL installation of a window is carried out and not otherwise.



People buy expensive windows and then the wall connection is wrongly made. Even the best window with the best insulation values is useless if installed incorrectly. And foam sealant is absolutely wrong in that case.

So if someone on their construction site sees that the windows are foamed in, they should intervene immediately.