Have torn up the floor in a room. Previously, there was scrap wood in the false floor with building paper on it. Now I have been recommended not to use anything organic. So boards are out. What should I use instead?
I have more than 55 cm between the floor joists, so ready-made false floor panels don't fit. I have read that some use polystyrene boards. Is that good?
What I like about the boards is that they can support walking on. It has been convenient now when I removed the floor. But as soon as the floor is finished, it doesn't matter at all how durable the false floor is as long as it can just hold up the floor insulation... The important thing is that it doesn't start to mold when moist air enters the foundation.
So, what do you recommend? Why?
I have more than 55 cm between the floor joists, so ready-made false floor panels don't fit. I have read that some use polystyrene boards. Is that good?
What I like about the boards is that they can support walking on. It has been convenient now when I removed the floor. But as soon as the floor is finished, it doesn't matter at all how durable the false floor is as long as it can just hold up the floor insulation... The important thing is that it doesn't start to mold when moist air enters the foundation.
So, what do you recommend? Why?
The best option is probably to lower the humidity at the base. I personally put plastic on the ground, closed the cat flaps, bought a dehumidifier (10,000 kr), and cut plywood for the subfloor. After a year, I'm still satisfied, and the foundation looks like it was newly built and is dry and warmer.
I replaced my old asfaboard panels with 50mm foam boards. Screwed from underneath with long screws and large plastic washers. In my case, it was not directly because they are inorganic (the foundation is bone dry), but it became additional insulation that is also windproof!
However, they are absolutely not meant to be walked on, which I quickly realized when my right leg went right through when I happened to step a little awkwardly while balancing on the beams on top. A little foam and putting back the piece that came off and it was quickly fixed though!
I did the same as vectrex but used 100mm foam boards instead, I also stepped sideways balancing on the floor joists one too many times and was very surprised, it held up to stand on. So the wind barrier I've stapled on the underside of the floor joists, which was supposed to support the mineral wool in case the foam boards sagged down after x number of years, feels a bit like overkill.
I don't have a regular crawl space. The "crawl height" in my foundation is a maximum of 10cm below the floor joists. In some, few, places no more than 2cm. So it's difficult to fit a dehumidifier. Also, there are no inspection hatches/entrances to the foundation.bygglalli said:
I can't reach to screw from underneath, so my styrofoam will have to lie on strips that I screw/nail to the sides of the floor joists.vectrex said:
Good to know that 5cm styrofoam doesn't hold up to being walked on!
So you need to be at 10cm for it to hold up to walking. Unfortunately, I think 10cm is too thick for me. Then I won't have room for much wood shavings between foam and the interior floor! I won't have any plastic between insulation and the floor, so I want some insulation that can absorb and release a little moisture. The wood shavings have worked well for the past 60 years, so I plan to continue with that. (I would have liked to use cellulose wool instead, but I think it would be too expensive compared to the wood shavings.)Drömhus2012 said:
Since you're going to put foam plastic between the floor joists, you're losing the argument for not having organic material downwards. Now, I think it will still work. Normally, there is no vapor barrier at all in a wooden joist floor over a crawl space. The ability for vapor to go downwards is significantly less than upwards towards the attic floor. I would see it as an advantage to have thicker foam plastic as it insulates significantly better than wood shavings!
The only risk is that because you get a better insulated floor, less heat will leak down into the crawl space, and thus you risk higher relative humidity down there.
The only risk is that because you get a better insulated floor, less heat will leak down into the crawl space, and thus you risk higher relative humidity down there.
I know. A little organic material is better than a lot?... I'm not sure how to think about this.vectrex said:
Good point.vectrex said:
This is important. I've seen what a difference of a degree colder can do to an attic...vectrex said:
I actually think that in your case there would be much gained by placing the foam under the joists. All organic material would then be at least 5 cm into the insulation and would thus have a significantly higher temperature. This in turn means that the risk of harmful high humidity decreases drastically on everything except the ground and the outside of the foam.
You write that it's cramped, but shouldn't it be possible to squeeze down the foam between the joists from above? Foam board can easily be glued in place, for example. Definitely more troublesome than placing it between the floor joists, but on the other hand, you avoid cutting each foam board, which is a nightmare in itself (static foam beads everywhere).
You write that it's cramped, but shouldn't it be possible to squeeze down the foam between the joists from above? Foam board can easily be glued in place, for example. Definitely more troublesome than placing it between the floor joists, but on the other hand, you avoid cutting each foam board, which is a nightmare in itself (static foam beads everywhere).
Masonite and asfaboard tend to sag.
I think 10 mm construction plywood has been the best.
Easy to cut and to seal against air leakage along the edges with outdoor sealant.
Whether it's organic or not doesn't matter much. The floor joists are probably made of wood, right?
I think 10 mm construction plywood has been the best.
Easy to cut and to seal against air leakage along the edges with outdoor sealant.
Whether it's organic or not doesn't matter much. The floor joists are probably made of wood, right?
OSB will probably work just as well.
It just wasn't available when I renovated 19th-century houses, so that's why I used plywood.
Construction plywood was reasonably cheap back then anyway.
It just wasn't available when I renovated 19th-century houses, so that's why I used plywood.
Construction plywood was reasonably cheap back then anyway.