We have a house from 1981 with a concrete slab foundation. On the concrete, there is 60 mm of foam insulation, on top of that plastic sheeting and 20 mm of particleboard.
Last Christmas, we discovered a water leak from the built-in water tank of the toilet. It has been going on for some time. Now a large part of the floor has to be removed. It is clearly visible where the water has been.
My question: should I put new foam insulation directly back on the slab, or should I use another construction method? The concrete looks completely dry next to the water damage.
Last Christmas, we discovered a water leak from the built-in water tank of the toilet. It has been going on for some time. Now a large part of the floor has to be removed. It is clearly visible where the water has been.
My question: should I put new foam insulation directly back on the slab, or should I use another construction method? The concrete looks completely dry next to the water damage.
If it has been good before according to you, then why change the construction, make it as it looks today
Of course, there can be problems with slab-on-grade, but not everyone experiences them. You can see how it looks when you lift the insulation; if it's black underneath, then it's not good, but if there's nothing, just concrete and it's dry, then it's OK.
The fundamental problem with non-insulated slabs is that water vapor in warm indoor air condenses when it meets the cold concrete, keeping it damp. This is primarily an issue associated with houses from the 1970s. A house built in 1981 should have some form of insulation even beneath the concrete. Additionally, 60 mm of foam on top is quite little. The plastic film under the chipboard prevents water vapor in the air from penetrating down towards the concrete. Problems arise mainly where there is no insulation or plastic film, such as at the sills of partition walls. The type of leak you experienced should not occur. Silicone seal toilet bases so you don't have to perforate the waterproof layer.
vapor barrier first, then foam plastic, particle board, and your surface layer.
actually, a tip is rag paper between foam plastic and particle board
actually, a tip is rag paper between foam plastic and particle board
Vapor barrier should always be on the warm side.
so you're saying not to follow what the cellplast manufacturers write?J justusandersson said:
It is basic building physics. Cellplast is vapor-resistant but not vapor-tight. However, since cellplast tolerates moisture, the consequences are not that significant.
and I have done around ten ground floor apartments with plastic first.J justusandersson said:
and this was done according to all the existing regulations
I have described what I believe is physically correct in building physics and argued for it. I can't do more than that.
Plastic against the concrete is for ground moisture. Plastic on the warm side is against moisture in the air. Vapor pressure downward is minimal as the warm air carrying moisture that can condense rises towards the ceiling. Imagine the house is upside down and the heat with moisture flows from heat sources down to the peak of the roof.
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Ground moisture is probably the least of the problems. Most concrete slabs, at least since the early 1950s, have been poured on a layer of capillary-breaking crushed stone. Even though the warmest air is located at the top of a room due to its lower density, it doesn't mean one can neglect insulating building components like exterior walls and floors.
Concrete slabs poured on an insulating layer almost never have moisture problems.
Concrete slabs poured on an insulating layer almost never have moisture problems.
exactly "almost never".J justusandersson said:
