Exterior plaster is uneven, window sills are too short, tightness of the ETICS (External Thermal Insulation Composite System)

But first, you have to find a lawyer who dares to take it on.

One has to find a lawyer first who dares to do it.

Oh, one can surely find someone from another jurisdiction. It should be an administrative law specialist.

So you finish with the roofing membrane and barely any air can circulate through the eaves in the cold roof space. Could that really be the sole reason?

Ultimately, the vapor retarder (not the barrier) must be multiply leaky anyway, as evidenced by the various moisture hotspots.

With all due respect to , back to the topic.

I would have thought that the humidity condenses most where it is cold – in your case where air circulates under the roof, or am I thinking incorrectly?

My general contractor always warned us that the cold roof would lead exactly to the consequences you are seeing. Whenever I go up through the floor hatch, a lot of water will condense on the ceilings in winter. The vapor retarder/vapor barrier will then be in the attic floor, and the floor hatch is sealed. Is it something like that, or have I misunderstood?

What about the blower door test? Did it leak anywhere?

With all due sympathy for , back to the topic.

I would have thought that humidity condenses most where it is cold – in your case, where air circulates under the roof, or am I mistaken?

My general contractor (GU) always warned us that a cold roof would have exactly the consequences visible in your case. Whenever I go upstairs through the attic hatch, a lot of water will condense on the ceilings in winter. The vapor barrier/vapor retarder will be in the attic floor in our case, and the attic hatch is sealed. Is it something like this, or have I misunderstood?

What does the blower door test say? Was there any draft detected?

Our building supervisor thinks that the ETICS insulation boards are installed too high (they end flush with the roofing membrane). They should have actually stopped inside the roof box. The ventilated roof box only ventilates itself but not the cold roof. The moisture simply cannot escape. He also recommended replacing the wool insulation above the vapor retarder, because once wet it no longer fulfills its insulating function and simply creates a new thermal bridge. A roofer who is a friend of a friend said that they usually cut the underlay membrane at the ridge so that no moisture accumulates?

The blower door test has not yet been conducted. Apparently, the general contractor only does it at the end, shortly before handover. Which is nonsense of course. Ideally, it would be done after installing windows/front door and establishing the vapor retarder. At this point, it is becoming increasingly expensive to fix leaks afterwards. We have urged the general contractor to carry out the test promptly.

Apart from that, in the room with the first water bubble on the ceiling (now also another one in a different room), there is a moisture spot on the wall that is getting bigger – see picture. Behind it is no pipe or duct, only exterior masonry. Moisture from the attic should not be able to pass either, since the ring beam seals the Poroton blocks. Or is migrating roof moisture behind the sheathing of the ring beam conceivable, which creeps behind the interior plaster?

Furthermore, the window sealing tapes on the inside are leaking or partially detached in more than half of the cases. At least there are drafts. Combined with the unsealed exterior windowsill, nothing good comes out of that. Our building supervisor thinks that the windows would be sufficiently sealed by plastering in the interior windowsills?

I’m curious when someone from the general contractor will show up here to determine measures. As building owners, we are not allowed to interfere with the construction process, but we have nevertheless made it clear to the drywall installer that he should not first panel the ceiling towards the roof. At least not until it is properly sealed here and no more puddles occur.

Oh, and the ventilation grilles of the indoor heat pump freeze up at the edges (where the system leaks), so that the exterior plaster is also damaged there.

Otherwise, there is still a damp spot on the wall in the room with the first water bubble on the ceiling (meanwhile also another one in another room), which is getting bigger - see picture. [...] Furthermore, the window sealing tapes on the inside are leaking or partially detached in more than half of the cases.

May it also be of use to you that, in my opinion, you document the defects quite exemplarily (especially the dated outline around the damp spot!). The improper use of branded adhesive tapes would almost be funny if it weren’t such a tragedy. Instead of "Würth," the tapes could just as "usefully" but impressively say "Calvin Klein" or "Veuve Cliquot" :-(

The blower door test has not been carried out yet. Apparently, the general contractor only does it at the very end, shortly before handover. Which is, of course, nonsense. Ideally, it should be done after installing the windows/front door and establishing the vapor barrier. At this point, it is becoming increasingly difficult to rework leaks. We have urged the general contractor to carry it out promptly.

I feel so sorry for you, this is a tragedy. Even you, as a layperson, know when it should be done.