ᐅ Is a vapor barrier necessary in the basement with waterproof concrete and underfloor heating?

Hello everyone,

Since the roof is currently being worked on, the roofer asked me if he should also install a vapor barrier in the basement. I pointed out that the concrete used is waterproof concrete, but he replied that while the floor and walls are resistant to water under pressure, they are not vapor-tight.

Is he just trying to generate extra business, or is he correct?

Thinking one step further: assuming I agree to have this vapor barrier installed, won’t other trades (electrical and plumbing) be drilling holes through it and thus making it ineffective?

By the way, our basement will be fully equipped with underfloor heating. Isn’t that enough to remove any potential moisture coming from the ground?

Thank you very much and stay healthy!

Hi,

Seriously? Waterproof against pressurized water but not vapor-tight? I’m laughing out loud here. In some cases, that could actually cause condensation and consequently mold between the vapor barrier and the concrete in the walls. So no, no vapor barrier on the walls. It’s used on the floor slab only if it hasn’t dried long enough. The idea is to prevent residual moisture from evaporating into the screed and, in rare cases, condensing. The barrier applied there is specifically designed for this purpose and not just leftovers from what remains from the roof.

Regards,
Nika

Glad I could cheer you up.

Why are you making fun of it? If I knew, I wouldn’t be asking for advice.

Could someone with expertise possibly respond?

Oakland schrieb:

Glad I could cheer you up.

Why are you making fun of it? If I knew, I wouldn’t be asking for advice.

Sorry, I wasn’t making fun of you, but rather questioning the business sense of your roofer. You did the right thing by not believing everything the professional says and asking for further clarification.

I actually had the same question when I was building, and I found expert reports from building surveyors online addressing this. What I wrote was the main essence of those publications.

Regards, Nika

The vapor barrier should, of course, be applied only to the floor and extend just 20 cm (8 inches) up the walls, which corresponds to the height of the floor structure.