Cracks in the interior plaster / window reveal

Hello everyone,
I have inherited a 1960s apartment. The apartment has relatively large plastic window sashes in some rooms, some about 180 cm wide, which were renewed about 10 years ago. While clearing out, I have now noticed that some windows have cracks in the plaster on the ceiling inside, see photos. I understand that plastic windows expand depending on temperature and certainly also move under wind load.... BUT: if you push against the window frame at the top from the inside outward, you can move it a few millimeters, about the width of the crack. To me, it feels as if the window frame was not installed correctly – or is this normal and the connection to the ceiling plaster just needs to be elastic? Since the apartment is going to be sold, I would appreciate an assessment of how serious the problem is and how it can be professionally fixed.

Morning,

yes, that is normal. Especially with the wide windows, the movements caused by wind load as well as deformation due to heat/cold are quite large, so that tears can appear in an elastic seal (this will happen repeatedly) and with a rigid surface application, cracks in the plaster could become apparent here.

Best regards, Jann

Hello Jann,

thank you very much for the reassuring response. That means a joint with elastic sealing would be the better solution, even if there will eventually be cracks.

What still surprises me is that the frame can be moved at the top by strong finger pressure, but is rigid at the bottom. I would have expected it to be firmly connected to the ceiling/the lintel at the top as well.

Best regards
k-man

So actually, nowadays a window is only firmly anchored on the sides in the reveal. Additionally, there is a load transfer downwards. Upwards, there is only the sealing. However, it shouldn't wobble even with light finger pressure. To me, this suggests that something isn't quite right with the sealing, and maybe in the upper third the side anchoring is either missing or has somehow come loose.
Warning: I am a layperson and only trained by installing my own windows with my father-in-law (30 years a window fitter). So it may be that in the 60s there were other mounting methods that were permissible.

yes, that is normal.

:oops: - if that is normal, I wonder which cracks would be abnormal?

What can be seen in the photos must never happen. Not in this form.

Well, we have a thermally induced component shortening. The sealant adheres more strongly to the frame than to the wall / wall paint and thus tears off. Since these shortenings (or expansions in summer) cannot be prevented, fastening elements must also be chosen so that they can accommodate these movements. All this information can be found in the corresponding standard.

I would claim that this crack width no longer occurs in summer.