Vapor barrier under parquet flooring with intermediate joists and underfloor heating?!

[avendere]

Hello!

I have searched but haven't found an answer to my specific problem.

The conditions are a 1.5-story house, intermediate floor, and water-based underfloor heating.

The "problem" is that there is a vapor barrier behind the ceiling drywall on the ground floor, and according to the parquet manufacturer’s instructions, there should also be a vapor barrier directly under the floor on the upper floor with underfloor heating, i.e., double vapor barriers on both sides of the joists.

My first thought was to skip the vapor barrier entirely since there is already one deeper in the construction, but in the flooring manufacturer's (I think it was Kährs) instructions, it "under no circumstances" should be as deep as on the other side of the joists to count.

What I'm considering now is whether to install a vapor retarder under the floor on the upper floor instead as a compromise? My idea was that it slows down a large part of the vapor pressure you want to avoid, while allowing any moisture to breathe out over time. But maybe it doesn't benefit the floor anyway, and if so, it's unnecessary...

Does anyone have some input on this? I'm more interested in what works in practice than what the surface layer manufacturer "requires" (cheaper to replace the floor than the joists =)).

Grateful for answers!

Best regards, Marcus

 

[KnockOnWood]

What function would the vapor barrier in the intermediate floor actually serve?
The fact that there is plastic over the ceiling plaster of the ground floor is probably just a leftover from the time before the attic was converted and heated.

But call Kährs and ask what they mean, will you! But make sure to talk to a technician

 

[avendere]

Yes, the function is controversial, to put it mildly, but essentially it is about the heat creating a vapor pressure that makes its way up into the floor and causes gaps and/or other issues. A vapor barrier is supposed to prevent this.

All manufacturers firmly claim it is needed, even in floor structures and even if relative humidity is below 60% with underfloor heating, I am skeptical and choosing between skipping it entirely or installing a vapor retarder. Double waterproof layers must be the worse of two evils.

There must be many who stand/have stood before the same problem? Funny that you can't Google an answer to this in 2018...

 

[Rabbithole]

In the intermediate floor, nothing is needed at all. There is equivalent temperature on both sides of the floor. If it's on one side, it probably won't do much harm, but I would avoid doubling it.

 

[avendere]

I agree instinctively, but this is what Kährs themselves write about underfloor heating:

SPECIAL REQUIREMENTS FOR INSTALLATION OF UNDERFLOOR HEATING:

• The floor construction must have a heat-distributing layer that provides an even temperature across the entire floor surface, so that the temperature does not become too high at certain points.
• It must be possible to regulate and limit the surface temperature with great precision.
• The entire floor surface must be heated. However, this does not apply to comfort heating systems that complement normal heating. In such cases, the temperature should be significantly lower than the allowed 27 °C at the floor surface.
• The laid floor, including the intermediate layer, must have low thermal resistance.
• A vapor barrier must be built into the floor construction and placed as close to the wooden floor as possible. If the floor joists are thick or heavy, it is especially important to have the vapor barrier close to the wooden floor. The vapor barrier must not under any circumstances be placed on the opposite side of the floor joists.

However, this statement does not specify whether it concerns a mid-floor or a crawl space, but it is indicated that the requirement for a vapor barrier also applies to mid-floors.

 

[avendere]

Got a response from Kährs now that in my specific case, the vapor barrier/brake should be skipped entirely. I assume the text above applies to crawl spaces or similar joists, so I will follow their advice!

 

[Barfot]

Hello!

I have searched but haven't found an answer to my specific problem.

The situation is a 1.5-story house, intermediate floor, and water-based underfloor heating.

The "problem" is that there is a vapor barrier behind the ceiling drywall on the ground floor, and according to the parquet supplier's instructions, you should also have a vapor barrier directly under the upper floor with underfloor heating, i.e., double vapor barriers on either side of the floor construction.

My first thought was to skip the vapor barrier entirely since there is already one lower down in the construction, but the flooring supplier (I think it was Kährs) states in their instructions that it "under no circumstances" can be as deep as on the other side of the floor construction to count.

What I'm considering now is laying a vapor brake under the floor on the upper floor instead as a compromise? My idea was that it retards a large part of the vapor pressure you want to avoid while allowing any moisture to breathe out over time. But maybe it doesn't benefit the floor anyway, and if that is the case, it's unnecessary...

Does anyone have some input on this? I'm more interested in what works in practice than what the surface manufacturer "requires" (cheaper to replace the floor than the floor construction =) ).

Grateful for answers!

Regards: Marcus

I have the same problem and have called Kährs, and what they say is that the lacquer on the wooden floor is extremely tight, which is why they recommend laying a vapor barrier. But since I have a waterproof layer in the ceiling of the basement, I will skip a vapor barrier under the parquet to avoid the floor construction becoming completely enclosed and risking a bigger problem. So I have placed 3 mm masonite (board) under the parquet and a felt paper to have a barrier that partially lets through and also ensures that I can lay the parquet along with the lath that holds the water-based heating pipes.

 

[avendere]

I have the same problem and called Khärs. They say that the lacquer on wooden floors is extremely dense, which is why they recommend laying a vapor barrier. But since I have a waterproofing layer in the ceiling of the basement, I will skip a vapor barrier under the parquet to avoid completely enclosing the beam layer and risking a bigger problem. So I have laid 3 mm masonite (board) under the parquet and a felt paper to create a barrier that partially allows passage and also allows me to lay the parquet along with the sparse panel that holds the waterborne heating pipes.

This was a while ago (wrote the post in 2018) so I can gladly report that after 4 years without a vapor barrier, the floor is still in pristine condition (minus the kids' "natural" patina). As I said, better to risk the surface layer than the beam layer.

Best regards: Marcus