Roof interior insulation incorrectly executed - major damage caused

Hello!

I have to turn to the collective knowledge here.

In 2017, we bought a house from 1921, the roof is from 1993 and has a diffusion-tight (!) underlayment, which was common at that time. In 2017, we converted the attic and had it newly insulated by a drywall installer. For this, the structure was doubled, the insulation wool was pressed tightly against the underlayment, then came insulation below the rafters, followed by the vapor barrier foil, and then the drywall.

So far so good. Now, at Christmas 2023, we had a storm/rain damage because the connection from the chimney to the roof became leaky. The roofer lifted some tiles there and saw water everywhere. Condensation is present all over the roof between the insulation and the underlayment; he looked under the tiles from the outside on all sides of the roof. Subsequently, we opened a part from the inside; everything was wet (far outside the chimney area—around the chimney damage, the insulation was soaking wet from rainwater, in the rest of the roof it is "only" condensation between insulation and underlayment). The roofer told us the interior insulation was done incorrectly. The insulation should never have been pressed directly against the airtight underlayment but should have been realized with several centimeters of ventilation. Now all the moist insulation wool has to be removed, huge effort, big costs. The leak at the chimney was sealed and a proper repair must be done there in spring, but this must be clearly separated from the condensation damage. The condensation damage would probably only have been noticed once the drywall had gone moldy.

What do you think? Does anyone have experience with this and any tips/ideas/suggestions? Can the drywall installer be held accountable? There is already slight black mold on the beams and all the insulation plus drywall must be removed, discarded, and replaced. I estimate the cost at roughly 10-15,000 EUR. Only the thinner insulation mats of the insulation below the rafters are dry and can possibly be reused. We cannot hope for goodwill from the drywall installer. We would like to hold him responsible if possible; after all, we hired a professional company back then to prevent exactly such a thing from happening. We paid a considerable amount of money back then and it was only 6 years ago.

Unless you have agreed on a separate warranty, it generally ends after 4 or 5 years depending on the type of contract, and you basically can do nothing more. Unless you can prove fraudulently concealed defects - which sounds rather unlikely here. You can check what was offered to you or charged at that time.

The story with the roof and the insulation has actually been going on for a while. We first suspected something in 2019 and then had drywallers and roofers come. In the end, they agreed that it was only a limited damage because there were 2 staple needle openings that were not sealed. We let it dry out and then closed it again. Despite endless calls, the roofer never showed up for the promised roof inspection and we then thought it was okay and dried out and left it at that. At that time, it was only 2 years ago – does that make any difference?

The problem is: if you rely on professionals, you are abandoned. But how are we supposed to know about this as laypeople? You really have no chance to notice something like that – and if so, it’s too late.

That is really tricky. I would probably first hire an expert. If this expert certifies that the drywall installer executed the construction against regulations (standards, ARdT, etc.) that were already in effect at the time, that falls within the realm of fraudulent/intentional behavior and you might have some legal (partial) success with a bit of luck. If the expert gives you little hope there, your only option is to gamble and try to get the drywall installer to contribute to the costs of the renovation to protect their reputation. The problem with drywall construction is that it is not a profession that requires a master craftsman certificate to register a business. In other words, there are many bunglers operating in this trade.

The contracted drywall installer also partially works on public projects. So we thought he was actually reputable. After reading a bit about fraudulently concealed defects, I will first seek an initial consultation with a specialist lawyer. Since we have a diffusion-tight mesh foil, ventilation was actually unavoidable; at least, that is what is stated everywhere. Only with a diffusion-open underlay membrane could the ventilation have been omitted. In this respect, the damage was foreseeable. Depending on what the lawyer says, we will talk to the drywall installer. He obviously will not admit, "Sure, it was my fault, I will do it properly again." Then we will have to see what to do next. For now, we are waiting to see what the lawyer says.

but now you have done some reading and realized that it was not executed correctly. Why didn’t you do that before or during the creation of the trade? It really wasn’t that much effort to google, was it?

Sure, professionals should do their trade properly. But you’re no longer 20 and you already had quite a bit of life experience, didn’t you?

At least during the construction period, I tried to roughly understand every trade and do a plausibility check for myself to see if it could be correct as executed. In addition, the master builder on site, who was related to us, paid close attention to the correct execution of many trades. Still, I certainly don’t want to say that everything went perfectly with me/us.

Why don’t “laypeople” get a paid expert for supervision who speaks for the builder? (I explicitly include myself here despite having a draftsman’s training (civil and road construction ;-) and half a civil engineering degree)
Without my brother (civil engineer FH) and the master on site and consultations with our architect (partly performance phase 5), we would certainly have hired someone like that too.