How soundproof are windows?

: I would also be interested in the information on this.

My problem is similar to the thread starter's. I suspect that the connection of the windows to the outer wall structure is faulty in my case. The windows are only set about 2 cm into the outer wall and the rest of the depth is in the insulation layer. Around the window, the window installer then glued thermal insulation boards/Styrodur and sealed the gap to the window with foam.

In the insulation layer above the window, there is also a roller shutter installed between the lintel and the brickwork (no additional sound insulation visible to me).

Can anyone help with this? Thanks.

The windows are only set about 2 cm into the backup masonry

By that you presumably mean the inner leaf of a cavity wall.

I suspect that the connection of the windows to the backup masonry is faulty in my case. [...] Around the window, the window installer then glued thermal insulation boards/Styrodur and sealed the gap to the window with foam.

I wouldn’t call that a suspicion: anyone who “seals” with foam might as well bark at the moon. I believe this is discussed even more frequently in the green forum (construction experts forum) than here, but I haven’t saved any references from either.

Many window suppliers nowadays "understand" the purpose of the installer to be that he somehow screws the delivered windows into the house in order to trigger the customer’s payment. If the installer did that bare-handed, the show effect would be about the same as with whipped cream around the window frames: the audience cheers, but it doesn’t really help ... ?

In the insulation layer above the window, there is also a roller shutter installed between the lintel and the facing brick (no further soundproofing is apparent to me).

I can’t say anything about connection details there, I have never had such cases and therefore not in complaints handling either.

: thanks. What would a professional sealing (without foam) look like?

The "popes" RAL and ift provide guideline-like statements on proper window installation. I have nothing against foam – only against the misconception of foam as a miracle cure for any and all excessive disregard for precision.