Choice of insulation under underfloor heating on cast slab in extension
"An uninsulated concrete vault located between an unheated and a heated space will always become damp."
Well, that's not quite right?
There is no air that can condense on top of the vault because there is polystyrene/self-leveling compound/floor heating/tiles, and due to the floor heating and the insufficient insulation against the vault, it results in a concrete vault that is warmer than the air temperature below. Cold air does not condense on warm surfaces.
So why would the vault become damp?
A slab on the ground with insulation on top is a bit different. There, it's mainly due to ground moisture that it can become a problem, right? And if the floor doesn't have a moisture barrier or a complete moisture barrier above the insulation.
I would dare to go out on a limb and say that a slab on the ground with a proper capillary-breaking layer underneath and good drainage doesn't cause any moisture problems.
Well, that's not quite right?
There is no air that can condense on top of the vault because there is polystyrene/self-leveling compound/floor heating/tiles, and due to the floor heating and the insufficient insulation against the vault, it results in a concrete vault that is warmer than the air temperature below. Cold air does not condense on warm surfaces.
So why would the vault become damp?
A slab on the ground with insulation on top is a bit different. There, it's mainly due to ground moisture that it can become a problem, right? And if the floor doesn't have a moisture barrier or a complete moisture barrier above the insulation.
I would dare to go out on a limb and say that a slab on the ground with a proper capillary-breaking layer underneath and good drainage doesn't cause any moisture problems.
Yes, an uninsulated concrete vault located between an unheated and a heated space will always become moist. The only thing that can prevent this is a vapor-proof layer on the top side of the slab, but styrofoam/self-leveling compound/underfloor heating/tiles are not vapor-proof. I bring up the issue because henkop does not believe that humid warm air can move into the concrete. The thousands of problems with uninsulated slabs on ground from the 70s construction were almost exclusively due to water vapor in indoor air condensing in the slab. In fact, most moisture damage in basements is due to moisture in the indoor air. In the past, when uninsulated basements were common, there was only a low temperature in the basement and never any organic overlay on the floors.
I give my thanks and bows for all the help!
After a few trips to Rinkaby rör and some simple math, we've changed our minds. Since the slope is as steep as it is, the self-leveling compound will be heavy, cumbersome, and expensive. I calculated over half a ton of self-leveling compound for 15m2, which comes to about 4000:-. It's not worth the money and time/effort. So, I'm thinking of working with wood and skipping the tile (even though I love tile).
What do you all think of the following:
1. Cover the floor in the "vault" with underlay paper
2. Lay a durable plastic over it
3. Wedge sparse exterior panel/ceiling sparse 22x120 into level
4. Insert or buy stone wool and rake insulation into the space between
5. Lay heat distribution plates
6. Finally insert hose, cover with durable plastic, foam, and finally vinyl/vinyl or laminate.
And finally, insulate the basement ceiling with cell plastic.
After a few trips to Rinkaby rör and some simple math, we've changed our minds. Since the slope is as steep as it is, the self-leveling compound will be heavy, cumbersome, and expensive. I calculated over half a ton of self-leveling compound for 15m2, which comes to about 4000:-. It's not worth the money and time/effort. So, I'm thinking of working with wood and skipping the tile (even though I love tile).
What do you all think of the following:
1. Cover the floor in the "vault" with underlay paper
2. Lay a durable plastic over it
3. Wedge sparse exterior panel/ceiling sparse 22x120 into level
4. Insert or buy stone wool and rake insulation into the space between
5. Lay heat distribution plates
6. Finally insert hose, cover with durable plastic, foam, and finally vinyl/vinyl or laminate.
And finally, insulate the basement ceiling with cell plastic.
Humid warm air, I believe, has an extremely difficult time moving in concrete. After all, it is air, however, you are absolutely right that moisture and warm moisture can move, and it not only can but does so. At least in our house. Moisture is certainly a concern but it is to be drained in the future so I'm not thinking much about it. On the other hand, I was quite concerned about the ability of the foam to keep the heat from the coil staying in the extension and not sinking down into the concrete.justusandersson said:
Skip number 2. You can't have wood between two plastic layers. If you have foam plastic in the basement ceiling, you can't have a car there due to fire risk. Laminate floors are cold, but that might not be an issue if there is underfloor heating.
We have an uninsulated basement and I agree with you 100%. The damage or infestations we had were due to the choice to put plastic flooring on the floor and a nice wallpaper on the walls sometime around the 70s. We just had to tear everything down (plenty of growth), angle grind with diamond grinder, plaster, and then paint with silicate paint. One thing I'm pondering is whether the shower in the basement is also affected. I haven't seen anything but it smells slightly suspicious and there's painted fiberglass wallpaper on the walls.justusandersson said:
I am trying to express myself simply. Essentially, it is a movement on the molecular level. However, it belongs to the basics of thermodynamics that all energy seeks equilibrium.
Absolutely, it makes sense to skip that. However, it might be an idea to lay that plastic before pressing down the pipe, meaning plastic between the heat distribution plate and the pipe (did this on the kitchen floor because it creaked, uponor's solution). Or maybe that's a bad idea. Should I prime and cover the exterior panel instead? Could condensation form where the wood is?justusandersson said:
I'm not a professional in that type of underfloor heating solutions, but I think one should avoid diffusion-tight layers unless they are absolutely necessary. If the wood is on underlay paper and the basement ceiling is insulated, I can't see any moisture problem. I also don't think that the fiberglass fabric in the basement shower should be an issue, even if it is painted with plastic paint. But you should always get to the bottom of any bad smell in the basement.
That's not true. IF you have a very large moisture addition from the warm side, it may be true under certain conditions. But the mechanism is not that air penetrates the concrete. Air cannot penetrate concrete (except in negligibly small amounts). What happens is that the moisture condenses on the surface of the cold concrete and then penetrates the concrete through diffusion. If you have heating coils in the floor, no moisture can condense and thus no moisture can penetrate.justusandersson said:
That is also not true, it is also common for moisture problems in 70s slabs to be due to rising ground moisture. In cases where the problems are due to the condensation of humid indoor air, the conditions are entirely different than in the case of concrete vaults and underfloor heating. It is when you have an elevated insulated floor on top of the uninsulated slab. The elevated floor allows some circulation of air which can condense against the slab, causing moisture in the insulation and joists/sills. Thus, the organic material can mold.justusandersson said:
I would place the plastic layer between the wood and the concrete. The risk with the construction is not moisture in the concrete but in the wood, so that it molds. It feels completely wrong to enclose the wood between plastic and concrete slab.
All conditions affecting moisture migration depend on various parameters such as temperature differences and relative humidity. In many cases, the "right" circumstances are only present during a limited part of the year or perhaps never. However, one should not advocate potentially critical solutions at all. Especially not on a forum like Byggahus where many seek advice without either theoretical or practical competence!
Enclosing the wood between plastic and concrete is something I will never do even if it is okay to do in other cases. The problem I see is moisture from the concrete. Normally, a wooden floor is protected against moisture migration by laying age-resistant construction plastic between the piping and the floor. In my case, the "wooden floor" can start at the concrete and thus the vapor barrier should be there. So on second thought, it will probably be as I wrote from the beginning. Underlay felt, vapor barrier, wooden batten. But I am a bit indecisive now. You struggle a bit with yourself. I really want tiles and am now considering doing the following: I have 50-60 mm to work with.f91jsw said:
On the concrete slab in the vault I lay:
1. Underlay felt
2. Construction plastic
3. Wooden batten to get everything level, now I have about 50-60 mm to work with.
4. (22mm) 22mm sparse panel 20c/c and 16mm loop with heat distribution plate.
5. (36mm) 12mm floor gypsum
6. (48mm) 12mm floor gypsum
7. Primer
8. (61mm) Adhesive and tiles
What do you think about that?