ᐅ Concern About Vapor Barrier – Air Flow from Ceiling Vent

The pitched roof of our house is supposed to be insulated as standard: construction (from outside to inside): tiles – protective membrane underneath – insulation – vapor barrier – small air gap – drywall.

Yesterday, during the autumn storm, I noticed that there is a draft coming through the wall/ceiling outlets for the lamps. Shouldn’t it be completely airtight to the outside because of the vapor barrier behind them?
Should I be concerned, and how high is the risk of mold developing in the insulation? If damage occurs, how would it be repaired? Would the entire drywall in the roof slope/ceiling need to be removed and the membrane resealed?

Thanks for the help.

Did you not perform a blower door test with leakage detection back then? Is it a vapor barrier or vapor retarder, and what is the SD value? What type of insulation was installed, and is it vapor permeable?

If you provide me with the exact construction details, I can assist you better.

Basically, there should be no drafts, and it must be airtight. The work was not done properly.

Gunnar76 schrieb:
Should I be worried

Yes, it depends on the roof construction, but it is not healthy.

Gunnar76 schrieb:
How high is the risk of mold in the insulation?

Mold will take some time to develop. First, it will become damp.

Gunnar76 schrieb:
And how would the damage be repaired? Would the entire drywall in the sloped roof/ceiling really need to be removed and the vapor barrier re-glued?

That would only be necessary if there is no vapor barrier at all. Usually, only the connections are not properly made.
To check, you can carefully open up the drywall a bit around some outlets and see if the penetration of the vapor barrier has been properly sealed. The vapor barrier should be securely taped around the cables using approved adhesive tape.

If not: enlarge all openings in the drywall, tape the vapor barrier to the cable, and close it again.

Ceiling-to-wall connections are more difficult to check and repair, and you often only notice issues when it becomes damp because air leakage is minimal or hardly noticeable.

Until today, despite several inquiries, I have unfortunately not received any detailed documentation and only know what I learned during daily site visits at the time: the roof is built as described above – with a membrane acting as a vapor barrier, which essentially covers the insulation on the interior side. The roof is not insulated all the way up to the ridge, but only up to a ceiling that has been installed inside the attic space. Of course, there is also insulation on top of this ceiling, and above that is a small uninsulated loft accessible via an insulated pull-down ladder.

If I want to check again now, everything is covered with drywall, which I would probably need to remove. The question is: is it really necessary?

dertill schrieb:

Usually, only the connections are not properly executed.
To check, you can simply open up the drywall slightly larger at a few outlets and see if the vapor barrier penetration has been properly sealed.

... That is usually not the issue. The cable does not go through the vapor barrier; it comes up from the switch (chased into the wall) and then lies in the cavity behind the drywall – still on the inside of the vapor barrier.

Gunnar76 schrieb:
The cable does not pass through the vapor barrier; it comes up from the switch (chased into the wall) and then lies in the cavity behind the drywall – still before the membrane.

So you have an uninsulated installation space on the interior side of the insulation and vapor retarder. And at the penetrations, meaning the holes, you are experiencing drafts.

This does not necessarily indicate a leak in the airtight layer.

If you have openings for outlets at the bottom, light fixtures at the top, and a continuous cavity in between, air movement can occur there, similar to a chimney effect.

To rule out leaks in the airtight and vapor-tight layers, the only method that comes to mind immediately is measuring surface temperatures at the suspicious spots. Maybe someone else has better suggestions.