Is the vapor barrier in the roof vapor-permeable? Yes? No!

...and here my cousin, a carpenter by profession, did it with me, he said it is better to use those because moisture can escape in moderation. Structure here: concrete roof tiles, angled at 30 degrees, then a thick vapor barrier, overlapping and glued. Between the rafters glass wool, then the climate membrane. This is how it looked before insulation.

I know quite a bit about this and am happy to help you. So it depends on your insulation which membrane you use. There is also a moisture calculator and U-value online where you can calculate it.

A vapor barrier requires 100% clean bonding. Definitely do a blower door test afterwards; with acquaintances, it was so leaky that the test could not be carried out.

With a climate membrane, the advantage is that processing defects are not as critical as with the barrier. But these membranes are not unconditionally recommended either. Therefore, the exact construction must be considered.

I know a lot about this and am happy to help you.

Thanks!

The construction is currently as follows:
- Roof tiles
- Underlayment membrane airtight glued
- Stone wool (Klemmrock 035 240mm)
- Vapor barrier
- Gypsum fiber boards

Regarding the floor: In the attic, there are two rooms: bedroom and bathroom. Above the bathroom, there is an attic installed and the bedroom is open to the top. A controlled residential ventilation system is also installed.

Is this information sufficient for you?

I am now a bit confused. A vapor retarder requires 100% clean sealing. What exactly is a climate membrane? We currently have a vapor barrier.


I also assumed that a vapor retarder would be better and we initially planned with that. Maybe Bookstar can soon shed some light on why a vapor barrier was recommended in our case.

The above is actually a typo, I meant vapor barrier in the clean processing.

So the climate membrane works in both directions depending on the need. Some doubt the reliability of these films, as they haven’t been around that long either.

Your construction is completely correct and has been carried out like that many times. The catch is, absolutely no vapor passes through there. If you now have a leak, condensate will accumulate there and it will mold. That’s why it has to be 99.9% tight and cleanly sealed.

Your underlay membrane is hopefully around sd 0.02 or similar, so highly diffusion-open?

Then you could also use a climate membrane well, but choose one with a somewhat higher sd value. For example, Pro clima Intello.

A standard vapor retarder would be wrong! It has a rigid sd value of 2, which would be too little in case of doubt and your insulation could get soaked.

Ah ok, thanks for the clarification!

That means the vapor barrier is correct and a normal vapor retarder would have been the wrong choice. Do you mean a leak by an unsealed spot, like a hole, or for example also if the insulation doesn’t fit perfectly? How about the battens? At that spot you go through the foil, but the battens should seal.

Braas Ecotec was used as the underlay membrane.

What advantage would the climate membrane have? The foil is already installed, but I could change it if it’s worth it.

Basically, the rule is: airtight inside, permeable outside. This also applies to walls, windows, etc.

You want to prevent the warm and moist air from the interior from penetrating your insulation, as it would condense there and cause mold. Therefore, a vapor barrier must be installed on that side, which must be applied meticulously. There are adhesives, nail tapes, etc. for this purpose. A leak, for example, means a nail hole if no nail tape was used underneath. The insulation behind it doesn’t have much influence there. However, it should of course also be installed properly.

From the insulation towards the outside air, you want moisture to be able to escape, so something vapor-permeable should be provided here.