Hello dear forum,
I recently bought a house from the 1960s, and I am facing the following issue. Due to moisture caused by a faulty vapor barrier, the floor structure in the basement, which is used as living space, had to be stripped down to the concrete slab. The old floor construction was about 6 cm (2.4 inches) high. We want to keep the new floor build-up to a maximum of 6 cm (2.4 inches) to avoid having to adjust many doors, steps, and transitions in height. Otherwise, the costs would far exceed our budget.
Therefore, my question: Is there a sensible floor construction that would also provide some insulation? Our carpenter recommends a system with a vapor barrier, wood fiber insulation boards (Pavatex brand), and wooden plank flooring on top. This option has the advantage that you can skip the screed, saving 4 cm (1.6 inches) in height while still achieving decent insulation.
Can anyone provide information on how these wood fiber insulation boards behave if the vapor barrier were to let through some moisture? The contractor who carried out the demolition painted a nightmare scenario of mold forming under the wooden floors.
Many thanks in advance for your input.
Bumsi
I recently bought a house from the 1960s, and I am facing the following issue. Due to moisture caused by a faulty vapor barrier, the floor structure in the basement, which is used as living space, had to be stripped down to the concrete slab. The old floor construction was about 6 cm (2.4 inches) high. We want to keep the new floor build-up to a maximum of 6 cm (2.4 inches) to avoid having to adjust many doors, steps, and transitions in height. Otherwise, the costs would far exceed our budget.
Therefore, my question: Is there a sensible floor construction that would also provide some insulation? Our carpenter recommends a system with a vapor barrier, wood fiber insulation boards (Pavatex brand), and wooden plank flooring on top. This option has the advantage that you can skip the screed, saving 4 cm (1.6 inches) in height while still achieving decent insulation.
Can anyone provide information on how these wood fiber insulation boards behave if the vapor barrier were to let through some moisture? The contractor who carried out the demolition painted a nightmare scenario of mold forming under the wooden floors.
Many thanks in advance for your input.
Bumsi
For the basement, probably on a slope since it's the living room, I would mainly be concerned about moisture penetrating from below and around the base of the exterior basement wall, especially considering the building’s age. Is there any visible waterproofing or known solution for this?
I would also suggest using Jackodur/Wedi/or whatever – cement-coated, fiberglass-reinforced XPS boards. These boards are resistant to moisture, have an integrated vapor barrier, definitely do not absorb moisture from below, and can replace the screed—provided the floor covering does not transmit point loads. So, multi-layer parquet, solid wood planks, or tiles would be suitable. In that case, glue down 40–50 mm (1.5–2 inches) boards and then install the floor covering on top.
I would also suggest using Jackodur/Wedi/or whatever – cement-coated, fiberglass-reinforced XPS boards. These boards are resistant to moisture, have an integrated vapor barrier, definitely do not absorb moisture from below, and can replace the screed—provided the floor covering does not transmit point loads. So, multi-layer parquet, solid wood planks, or tiles would be suitable. In that case, glue down 40–50 mm (1.5–2 inches) boards and then install the floor covering on top.
First of all, thank you for the ideas.
Correct, the house is located on a slope! There was virtually no waterproofing. The plan is actually to install paraffin barriers with floor transitions to the vapor barrier at all walls adjoining the ground, to prevent any moisture from coming through.
@dertill Am I correct in understanding that with the XPS boards you would also skip the welded vapor retarder, or does that still need to be installed underneath?
@Bookstar
The assembly with the Pavatex boards would be done using special battens for the joints. My biggest concern is this: if moisture were to get into the floor structure for any reason, these eco-boards would probably develop mold quite quickly. I understandably have little desire to tear everything out and reinstall it from scratch again.
There was one more problem I forgot to mention. The concrete slab is quite uneven. Would that still work with your versions?
Correct, the house is located on a slope! There was virtually no waterproofing. The plan is actually to install paraffin barriers with floor transitions to the vapor barrier at all walls adjoining the ground, to prevent any moisture from coming through.
@dertill Am I correct in understanding that with the XPS boards you would also skip the welded vapor retarder, or does that still need to be installed underneath?
@Bookstar
The assembly with the Pavatex boards would be done using special battens for the joints. My biggest concern is this: if moisture were to get into the floor structure for any reason, these eco-boards would probably develop mold quite quickly. I understandably have little desire to tear everything out and reinstall it from scratch again.
There was one more problem I forgot to mention. The concrete slab is quite uneven. Would that still work with your versions?
Bumsi schrieb:
Do I understand correctly that with the XPS boards you would also skip the welded vapor barrier, or does it still need to go underneath?You no longer need a vapor retarder against moisture from the indoor air. However, I would still recommend sealing against moisture from the outside, as it can slowly enter through joints and at the edges.
What do you mean by uneven? The XPS boards are adhered with adhesive mortar or construction adhesive. If the unevenness can be compensated that way, no problem. Otherwise, a leveling compound must be applied beforehand. The boards should be glued across the full surface. Leveling with loose-fill insulation is not possible since the boards should not be installed as floating if there is no screed on top. Also, the total build-up height would no longer fit.
Retrofitting floor insulation in basements or in areas without a basement is always tricky regarding moisture. The ground keeps the underside permanently cool, which reduces drying out during summer (unlike roofs or walls).
Wooden battens with a vapor retarder and insulation mats placed between the battens can work, but I would feel uneasy about it, even though I generally try to build as "natural" as possible. Of course, this can also be done on uneven substrates.
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