Insulation on upper floor concrete ceiling / roof by own work - vapor barrier?

Hello dear members,

I want to insulate my upper floor ceiling or attic space with my own work.

Construction: 2 x 10 cm EPS WLG 035 and on top 1.5 cm OSB boards for walking on.

Around the edge on the outside, I will leave out the first row of OSB boards.

Now the question: Do I need a vapor barrier?

I keep reading the most varied opinions and recommendations.

Hello,

at the end of July, we insulated our upper floor ceiling together with the local master carpenter and created the cold roof (KfW70 house).

First of all, the roof frame was raised. A part of the vapor barrier was already laid under the collar beams. Then, very carefully, the vapor retarder was laid over the entire upper floor ceiling area. The seams were neatly sealed. Everything was also neatly sealed at the supports of the ridge beam and the chimney.

After that, we laid 2x12 cm EPS insulation boards staggered, covering the entire area up to the collar beams. Behind the collar beams (i.e., at the eaves), where we could not reach with the boards, we accordingly placed/stuffed glass wool. We also made sure to leave no spot open during the insulation!

Afterwards, we immediately installed the roof sheathing, the roofing membrane, and the counter battens so that no moisture could reach the insulation and the roof would already be watertight.

I hope I could help you.

Edit: I just noticed that I wrote Dampfbremse once and Dampfsperre once. However, I mean Dampfsperre consistently. This was recommended to us by the master carpenter.

That sounds very much like you have a wooden ceiling - but Harald asked about a concrete ceiling. Here I am quite sure that a vapor barrier is not needed, since concrete is almost vapor-tight by nature.

That sounds very much like you have a wooden ceiling – but Harald asked about a concrete ceiling. Here I am quite sure that a vapor barrier is not needed since concrete is almost vapor-tight by nature.

No, we also have a concrete ceiling and it is naturally diffusion-open to a certain extent – unless the ceiling is made of waterproof concrete (WU-Beton).

I suppose the vapor barrier prevents moisture rising from the rooms from migrating through the concrete ceiling into the insulation and thus "weakening" the insulation – because wet insulation is less effective. (Warning – layman’s opinion).

Hello,

No, we also have a concrete ceiling and it is naturally diffusion-open to a certain extent

Since when?

- unless the ceiling is made of WU concrete

WU stands for WaterUntight; this property is generally inherent in every concrete

Rhenish greetings