Hello everyone,
We are currently experiencing the first winter in our newly built house. After the recent cold days, I just noticed in the attic that we have mold on the gable side (OSB boards) and on the battens for the vapor barrier (see picture, mold not visible)
Some background about the building structure: The house is built using timber frame construction. The attic is part of the thermal envelope. The vapor barrier is therefore, as can be seen, located beneath the roof structure. The intermediate ceiling does not have a vapor barrier. Last year’s blower door test according to the energy consultant showed no defects.
What I find noticeable is that the mold seems to appear only on one gable side. Do you have any advice on how I should proceed or how to investigate the issue?
My initial thoughts:
- At some stapler points, the vapor barrier foil has torn from the staples. There are small tears the size of the staples in the foil (I plan to tape these up tomorrow first).
- Beneath the affected area is partially the bathroom. Between the ceiling and the gable wall there is a small gap that leads into the installation cavity of the bathroom wall. Could it be that moisture is entering the attic through this gap? (see picture)
-
- The attic hatch is generally insulated. However, around the frame of the hatch, there is a small open gap towards the ceiling. This gap is open to the bottom and only covered by the hatch’s trim panel.
As I understand it, the indoor air in the living space should not be a problem since the attic is included in the thermal envelope?
Thanks in advance for your help.
We are currently experiencing the first winter in our newly built house. After the recent cold days, I just noticed in the attic that we have mold on the gable side (OSB boards) and on the battens for the vapor barrier (see picture, mold not visible)
Some background about the building structure: The house is built using timber frame construction. The attic is part of the thermal envelope. The vapor barrier is therefore, as can be seen, located beneath the roof structure. The intermediate ceiling does not have a vapor barrier. Last year’s blower door test according to the energy consultant showed no defects.
What I find noticeable is that the mold seems to appear only on one gable side. Do you have any advice on how I should proceed or how to investigate the issue?
My initial thoughts:
- At some stapler points, the vapor barrier foil has torn from the staples. There are small tears the size of the staples in the foil (I plan to tape these up tomorrow first).
- Beneath the affected area is partially the bathroom. Between the ceiling and the gable wall there is a small gap that leads into the installation cavity of the bathroom wall. Could it be that moisture is entering the attic through this gap? (see picture)
-
- The attic hatch is generally insulated. However, around the frame of the hatch, there is a small open gap towards the ceiling. This gap is open to the bottom and only covered by the hatch’s trim panel.
As I understand it, the indoor air in the living space should not be a problem since the attic is included in the thermal envelope?
Thanks in advance for your help.
A
Allthewayup23 Jan 2026 20:01Please measure the temperature and humidity up there. If you don’t heat the attic, it probably gets too cold, and even a few percent increase in humidity can lead to mold growth.
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