Vapor barrier connection foot purlin / sealing

Hello everyone,

we noticed today during the Blower Door test that we apparently connected the vapor barrier incorrectly. Just a brief introduction: we built a two-story house with a hip roof and a 35° roof pitch. The heating and ventilation system is located in the attic. Therefore, we insulated both the wooden beam ceiling on the upper floor and the attic with 24 cm insulation and Isover vapor barrier.

Now to the issue. We glued the vapor barrier in the attic to the collar beam. This rests directly on the ring beam. During the Blower Door test, it was noticed that air flowed between the collar beam and the ring beam into the attic. I have now learned that we should have glued the vapor barrier up to the masonry.

How should we proceed best now? Would it possibly be sufficient to inject and seal the collar beam with silicone? The attic is only used as a storage space and for housing the heating/ventilation system. Or should I cut a 30 cm strip of the foil and connect the collar beam to the masonry?

I quickly made a sketch for better illustration. I would appreciate your tips.

You have already sealed the [OG] against the [DG]? And it still drafts in the [DG]? Then there must be something else wrong, or how is the sketch to be understood? Otherwise, without knowing any other boundary conditions, the second option (new strip) would be the correct approach for now.

Thank you for your quick response, I have uploaded another picture with the plan from the architect.

Is the intermediate ceiling insulated? Who came up with that? The arrangement doesn't really make sense. Regardless, it probably shouldn't matter for the blower door test, since apparently you do have a hole in the sealing to the attic, which is much more serious.

Exactly, the intermediate ceiling is also insulated. The roof had to be insulated because of the heating. We wanted the upper floor to be additionally insulated for soundproofing (all done by ourselves). It certainly won't hurt to have both insulated.

If we now extend the vapor barrier up to the ring beam, the problem should be solved, right? I had possibly hoped that the much simpler solution (sealing with silicone) would also be OK here. But we'd rather do it properly once.

Just to be sure again. We did the blower door test once with the attic stairs closed. Everything was fine then. In another test with the hatch open, there was a draft noticeable between the ring beam and the foot purlin.

It won’t hurt to have both insulated.

If not heated and not ventilated, it can indeed cause damage. It is definitely not particularly beneficial for the wooden structure.
Make sure to set up a temperature/humidity meter with a logging function.

Everything was fine there. In another test with the hatch open, you could feel a draft between the ring beam and the base purlin.

Oh, okay, then it doesn’t sound so bad anymore.
Silicone is not permanently airtight.