Forgot insulation on the dormer wall - mold on wood - what to do?

There is no independent construction supervision.

You should urgently change that. The site manager is an employee of the construction company, so he has a conflict of interest. And in this specific case, he should have done something even in case of a conflict of interest, as it is immediately noticeable. So I would assume negligence on the part of the site manager. And you want the expert who only represents their own interests for that as well.

In our contract, it is clearly stipulated that our general contractor also takes over the site management and, among other things, monitors the quality of the individual trades and intervenes if necessary.

I acknowledge that there is a conflict of interest, and we will possibly consult an expert on this matter.

But ultimately, that is not the issue.

I want to know the best way to deal with this moldy wall now.

Option A: Treat the wood (mold remover or similar) and let it dry, then install the insulation plus vapor barrier

Option B: Treat the wood (mold remover or similar) and immediately install the insulation plus vapor barrier

Or perhaps there is a completely different alternative.

Let the contractor propose something. You are the client and only need to point out the defect, not the solution.

I have the feeling we are talking past each other :D

The GU sent craftsmen to the construction site yesterday. They were supposed to install the insulation and vapor barrier. As a layperson, I consider this risky, which is why I sent the craftsmen away again yesterday. The GU did not inform us about this measure, and the craftsmen did not contradict me when I explained why I am now rejecting it.

It is important for me to know how to properly solve this problem. I would prefer not to be responsible later for the fact that professionally correct solutions could not be carried out on schedule.

At the moment, it is not about responsibility or anything like that, but really just about a professional opinion on how to proceed.

Formal letter in paper form! (Registered mail / return receipt) with the title "Complaint about defects". List what you believe is not okay - done.

Option A: Treat wood (mold cleaner or similar) and let dry, then install insulation plus vapor barrier Option B: Treat wood (mold cleaner or similar) and directly install insulation plus vapor barrier Or maybe there is a completely different alternative.

The "problem" at the moment is that you have warm, humid air in the house due to the screed drying and with the current outside temperatures around 0°C this immediately leads to condensation on the wooden board/exterior wall. You will not get it dry without further measures. In any case: First remove the mold and, for example, stop growth for the time being with a lime wash. Then ... Option A: Set up a fan heater blowing warm air towards the dormer/dormer wall and run it for 1 day. Then the dormer wall will be sufficiently dry because condensation does not occur due to the warm airflow or the board dries out. Immediately afterwards install insulation and vapor barrier on the inside and seal airtight! Of course, the fan heater should be electric, not a gas heater, which produces warm, humid air from the burned gas. Option B: Directly insulate the still wet board from the inside and seal as in A. Although the board is still wet, no more moisture will come in and over time the board will dry out. This should also work, but how fast this happens depends on the ventilation behind the metal cladding. Probably almost zero, so it will take until spring. I would convince the general contractor of Option A or initially ask him to present his plans for remediation. If these only include installing the insulation, I would push for Option A. Later the mold will be harmless there, even if some residual spores remain on the wood. If the wood no longer gets wet, it will not grow further and the spores are outside the living area. Given the presumably affected area, this is also uncritical.