Hello!
I am interested in purchasing a house where the concrete slab is insulated with 80 mm of overlying cell foam. On top of the cell foam is plastic sheeting and then 22 mm chipboard flooring.
Since I plan to replace the flooring throughout the house, I am also considering addressing the incorrect foundation construction so that I don't have to tear up my new floor due to future moisture problems.
If a solution can be found that also allows for hydronic underfloor heating, I would be really satisfied.
I'm thinking about installing a system for mechanical floor ventilation, but I'm not quite sure if and how this can be combined with underfloor heating.
I would like to get rid of the chipboard flooring since it can be attacked by mold. However, I am unsure how to put the whole scheme together. Should I leave the cell foam and plastic sheeting in place and replace the chipboard flooring with some mechanically ventilated material? Or should I tear up the cell foam and plastic sheeting as well and replace them with something else?
What does the expertise say?
I am interested in purchasing a house where the concrete slab is insulated with 80 mm of overlying cell foam. On top of the cell foam is plastic sheeting and then 22 mm chipboard flooring.
Since I plan to replace the flooring throughout the house, I am also considering addressing the incorrect foundation construction so that I don't have to tear up my new floor due to future moisture problems.
If a solution can be found that also allows for hydronic underfloor heating, I would be really satisfied.
I'm thinking about installing a system for mechanical floor ventilation, but I'm not quite sure if and how this can be combined with underfloor heating.
I would like to get rid of the chipboard flooring since it can be attacked by mold. However, I am unsure how to put the whole scheme together. Should I leave the cell foam and plastic sheeting in place and replace the chipboard flooring with some mechanically ventilated material? Or should I tear up the cell foam and plastic sheeting as well and replace them with something else?
What does the expertise say?
If it works, I don't think you should touch it...
If you want to do it completely right, you should break up the slab, dig out, insulate, pour a new slab...
Otherwise, before the insulation, you should lay nivell or platon with a ventilation system...
If you want to do it completely right, you should break up the slab, dig out, insulate, pour a new slab...
Otherwise, before the insulation, you should lay nivell or platon with a ventilation system...
I understand that it might seem crazy to tear up a floor before moisture damage has been confirmed, but partly I want to figure out approximately what it would cost to remedy before a potential purchase of the property, and partly I would like to install underfloor heating and replace the entire outer floor covering. But maybe it is unsuitable to install underfloor heating on that construction?
No major issue with that construction, provided that the concrete slab is clean and free from, for example, wood residues. The plastic sheeting prevents moisture migration upwards, just make sure it is taped or seamless.
My parents have a similar construction in their basement, and it works excellently.
Make sure to smell thoroughly in corners and such to confirm it's free from mold and sour odors from, for example, damp sills.
If you want underfloor heating, you can, for example, replace the chipboard with a grooved chipboard in which you then lay the heating coil.
My parents have a similar construction in their basement, and it works excellently.
Make sure to smell thoroughly in corners and such to confirm it's free from mold and sour odors from, for example, damp sills.
If you want underfloor heating, you can, for example, replace the chipboard with a grooved chipboard in which you then lay the heating coil.
But if the slab is wet and the plastic stops diffusion, there's a risk the moisture will go up into the walls instead.
If it's working well now, the slab might be sufficiently well-drained.
Otherwise, you'll have to break it up and excavate (expensive), lay tiles without underfloor heating that allow moisture to pass through, or use a ventilated floor system.
If it's working well now, the slab might be sufficiently well-drained.
Otherwise, you'll have to break it up and excavate (expensive), lay tiles without underfloor heating that allow moisture to pass through, or use a ventilated floor system.
Several other houses in the area have had issues with the sills, so I would like to take preventive measures even if they are not severely affected by rot yet. A ventilated floor should significantly reduce the moisture load on the sills even if the floor does not go underneath them. The question is whether it's suitable to use underfloor heating without insulation under the slab. Would it work to place the ventilated floor closest to the slab, then put foam plastic on top of the ventilated floor, and chipboard with channels for underfloor heating on top of that?
80 mm foam plastic and the ventilated floor may not have enough insulating effect to make underfloor heating suitable?
80 mm foam plastic and the ventilated floor may not have enough insulating effect to make underfloor heating suitable?
There is tracked polystyrene for underfloor heating, you don't need any chipboard at all but lay the parquet directly on the polystyrene. It is used by at least one house manufacturer in new constructions (on wooden joists with flooring chipboard, admittedly) so I assume it is an established method. Cheaper than putting mineral wool in the joist and tracked flooring chipboard is probably the reason for using this. If you don't have any moisture problems under the existing polystyrene, it might be a viable alternative.
LK recommended at least 3cm when we asked them a few years ago. We have 8-10cm polystyrene on the part of our slab that we cast on top of the old slab and we do not use large amounts of energy to heat the house, so it obviously works.
LK recommended at least 3cm when we asked them a few years ago. We have 8-10cm polystyrene on the part of our slab that we cast on top of the old slab and we do not use large amounts of energy to heat the house, so it obviously works.
The chipboard flooring will not be affected since they are on the correct side of the plastic, provided the plastic is intact. However, if you are concerned about the sill, there is probably nothing else that helps apart from replacing it. I wonder the following:
- Is the concrete slab drained?
- Are there moisture damages on the exterior walls?
- Has the facade/base been repaired somewhere? Moisture rising can cause the plaster to detach.
- Is there a proper moisture barrier between the slab and the sill? I have seen that mineral wool has been placed in between as a sound insulator.
- Is the concrete slab drained?
- Are there moisture damages on the exterior walls?
- Has the facade/base been repaired somewhere? Moisture rising can cause the plaster to detach.
- Is there a proper moisture barrier between the slab and the sill? I have seen that mineral wool has been placed in between as a sound insulator.
Thank you for all the tips and opinions!
The concrete slab is drained with gravel underneath. Around it, there are clay pipes in gravel. However, this is the original since 1977, so I am considering redoing it for safety reasons. The exterior walls are made of brick, and I haven't seen any signs of moisture there.
There are no visible signs that the façade/socle has been repaired.
According to the construction drawing I attached in the first post, there is only mineral wool between the sill and the concrete slab. It doesn't feel sustainable in the long run. Then it should be caulked with some form of sealing strip between the sill and the foam.
Do you think it's possible to save the situation with a ventilated floor on top of the slab, or is a sill replacement unavoidable? It's a theoretical question, of course, but several people guessing is better than one
The concrete slab is drained with gravel underneath. Around it, there are clay pipes in gravel. However, this is the original since 1977, so I am considering redoing it for safety reasons. The exterior walls are made of brick, and I haven't seen any signs of moisture there.
There are no visible signs that the façade/socle has been repaired.
According to the construction drawing I attached in the first post, there is only mineral wool between the sill and the concrete slab. It doesn't feel sustainable in the long run. Then it should be caulked with some form of sealing strip between the sill and the foam.
Do you think it's possible to save the situation with a ventilated floor on top of the slab, or is a sill replacement unavoidable? It's a theoretical question, of course, but several people guessing is better than one
The answer is that you have a risk construction.
I have seen a house with three concrete slabs: house, garage, and an extension between the garage and the house.
Undrained throughout the house.
Water presses in and rises to the sill in the garage, as it is the slab that lies the lowest in relation to the ground. Here, the sill and studs rotted where the water came through the ground. But this likely happened before drainage was installed for that specific wall.
Use your nose! If it smells fresh, then probably nothing has happened. In that case, you might not need to do much. You probably also don't need to worry about impurities on the slab either, since the sill should have already rotted if the slab was waterlogged.
If you can manage to switch to a ventilated floor, then the sill replacement is almost free.
What costs are the floors and the chipboard, just calculate, I would guess that a new floor costs 500-1000 SEK/sqm in material.
The sill costs a maximum of 30 SEK/lpm.
If it doesn't smell, I would have stayed put and done nothing, maybe a new floor to freshen it up a bit. However, I wouldn’t dare to go for floor heating, because I do not understand if it might disturb some balance.
I have seen a house with three concrete slabs: house, garage, and an extension between the garage and the house.
Undrained throughout the house.
Water presses in and rises to the sill in the garage, as it is the slab that lies the lowest in relation to the ground. Here, the sill and studs rotted where the water came through the ground. But this likely happened before drainage was installed for that specific wall.
Use your nose! If it smells fresh, then probably nothing has happened. In that case, you might not need to do much. You probably also don't need to worry about impurities on the slab either, since the sill should have already rotted if the slab was waterlogged.
If you can manage to switch to a ventilated floor, then the sill replacement is almost free.
What costs are the floors and the chipboard, just calculate, I would guess that a new floor costs 500-1000 SEK/sqm in material.
The sill costs a maximum of 30 SEK/lpm.
If it doesn't smell, I would have stayed put and done nothing, maybe a new floor to freshen it up a bit. However, I wouldn’t dare to go for floor heating, because I do not understand if it might disturb some balance.
Sure, the sill is cheap per linear meter, but the actual work to access and replace it won't be free even if I choose to do a lot myself. My hope was that I could avoid future sill replacement by installing a ventilated floor instead. I really like the house's location, facade, garden, etc., but the question is how much cost reduction I should demand in my own bidding calculation to compensate for potential future measures. According to the attached drawing, it seems that the sills for the load-bearing interior walls are directly against the concrete. These should be more susceptible to moisture than the sills along the exterior walls, which are likely ventilated a bit through ventilation openings in the brick facade. How much does it usually cost to replace a sill for a normal-sized villa if you hire someone to do the job?
All the costs I have seen are per sqm, probably because the floors are the dominant cost. But as you describe it, it's the load-bearing wall in the middle that is the concern. However, with the inspection, you can conduct an extended investigation and measure the moisture content in that specific sill. If it's low - do nothing.
From what I saw of the sill replacement, it didn't seem particularly complicated.
1. Get a reciprocating saw in the 4kSEK class, e.g., Milwaukee 1000??
2. Get many expensive good blades for the saw, e.g., Lennox Fire & Rescue
2b. Get a really good vacuum cleaner, preferably one where the debris ends up in a plastic bag.
3. Tear out all floors in the room down to the foundation.
4. Draw a line with a ruler where you intend to saw, preferably not above the skirting board, then you don’t need to redo the wallpaper.
5. Cut away the plasterboard with the reciprocating saw. Be careful with studs and electrical and water pipes.
6. Mark on the slab where studs for door frames are located - otherwise, there could be problems closing the door if the studs have shifted.
7. Now it's just a matter of sawing. Removing the sill between the studs becomes fairly easy.
8. Depending on how they look, remove the sill under up to three studs.
9. Put down tar paper and a new sill of regular timber.
10. Fasten the sill to the concrete slab with nail plugs, but buy quality first, buy at least a box of Essve or similar before trying the budget stuff from Biltema. I claim that Biltema’s nail plugs do not work. With the right drill in the hammer drill, you drill through the sill and concrete in one go. Then you drive in the nail plug with a hammer. Goes fairly quickly.
11. Attach the studs to the sill.
12. Restore the plasterboard. Cut approx. 50mm wide strips out of plywood, which you place on the back of the plasterboard along the seam. If you’re going to have a ventilated floor, you might instead need to insert an extra noggin between the plasterboards so that air can flow freely over the slab.
If you find something that is infested, you should replace the stud quite a bit, don't remember if you should replace 1m from the damaged spot or if half a meter is sufficient.
From what I saw of the sill replacement, it didn't seem particularly complicated.
1. Get a reciprocating saw in the 4kSEK class, e.g., Milwaukee 1000??
2. Get many expensive good blades for the saw, e.g., Lennox Fire & Rescue
2b. Get a really good vacuum cleaner, preferably one where the debris ends up in a plastic bag.
3. Tear out all floors in the room down to the foundation.
4. Draw a line with a ruler where you intend to saw, preferably not above the skirting board, then you don’t need to redo the wallpaper.
5. Cut away the plasterboard with the reciprocating saw. Be careful with studs and electrical and water pipes.
6. Mark on the slab where studs for door frames are located - otherwise, there could be problems closing the door if the studs have shifted.
7. Now it's just a matter of sawing. Removing the sill between the studs becomes fairly easy.
8. Depending on how they look, remove the sill under up to three studs.
9. Put down tar paper and a new sill of regular timber.
10. Fasten the sill to the concrete slab with nail plugs, but buy quality first, buy at least a box of Essve or similar before trying the budget stuff from Biltema. I claim that Biltema’s nail plugs do not work. With the right drill in the hammer drill, you drill through the sill and concrete in one go. Then you drive in the nail plug with a hammer. Goes fairly quickly.
11. Attach the studs to the sill.
12. Restore the plasterboard. Cut approx. 50mm wide strips out of plywood, which you place on the back of the plasterboard along the seam. If you’re going to have a ventilated floor, you might instead need to insert an extra noggin between the plasterboards so that air can flow freely over the slab.
If you find something that is infested, you should replace the stud quite a bit, don't remember if you should replace 1m from the damaged spot or if half a meter is sufficient.