Green Building Forum - U value of uninsulated concrete slab and options to improve

U value of uninsulated concrete slab and options to improve

djh — Tue, 30 Jul 2019 12:37:57 +0100

You can get the beading here too, but it's usually seen as a quick fix way to deal with retro-fitting. The best way is to use cork strips around the edges to stop the planks walking, and deep (thick) enough skirtings to cover whatever movement does happen.

U value of uninsulated concrete slab and options to improve

Kenny_M — Thu, 01 Aug 2019 09:53:04 +0100

Just wanted to say thanks all for the comments.

Plenty here for me to work from. I think what I am going to go for is about 20mm insulation and engineering wood flooring over the top. This is something that is easy to do myself in the time that I have - which is usually after 8pm when the wee one goes to sleep. I like the idea of a fully dug out, insulated slab, but just can't afford the cost and disruption, and the length of time it would put our main living/kitchen area out of action. Even having a rug down in this area made a massive difference last winter, so 20mm of good insulation should be transformative.

U value of uninsulated concrete slab and options to improve

Jeff B — Thu, 01 Aug 2019 13:25:17 +0100

Posted By: Kenny_MJust wanted to say thanks all for the comments.

Plenty here for me to work from. I think what I am going to go for is about 20mm insulation and engineering wood flooring over the top. This is something that is easy to do myself in the time that I have - which is usually after 8pm when the wee one goes to sleep. I like the idea of a fully dug out, insulated slab, but just can't afford the cost and disruption, and the length of time it would put our main living/kitchen area out of action. Even having a rug down in this area made a massive difference last winter, so 20mm of good insulation should be transformative.

I agree. My philosophy is that something has to be better than nothing. I know from a purist point-of-view that is not acceptable but there comes a point where practicability has to take precedence over theory. I would have liked to have done a dug out insulated slab here too but it is simply not practicable to do so. If you are thinking of 20mm EPS then I would recommend using some DPM under the wood flooring in case of squeaks, as I said in an earlier post.

U value of uninsulated concrete slab and options to improve

mark_s — Sun, 11 Aug 2019 18:28:29 +0100

I replaced a floor by filling with insulation boards, chipboard with 2x3 on top supporting oak boards. Water pipes and cables run in the small void.

Just to comment on the wool underlay - we had a nightmare with it getting clothes moths in it. Ended up having to replace lots of underlay and carpets and deeply regret ever having it.

U value of uninsulated concrete slab and options to improve

Kenny_M — Sun, 18 Aug 2019 19:50:33 +0100

Just wanted to clarify something. If I have been following this right people are saying to put the damp proof membrane on top of the insulation, rather than below?

If I lift the tiles (considering doing this as current tiles are not level, would I also need a damp proof membrane between the concrete slab and the insulation on the other side?

U value of uninsulated concrete slab and options to improve

tony — Sun, 18 Aug 2019 20:33:58 +0100

I never put a membrane under the insulation, on top it acts as a vapour barrier too.

Under it can act as a bucket that can collect water during construction, leaks and in extreme cold condensation.

I have see this kind of water last 8 years without dissipating.

On top for me, (once an insistent building inspector insisted it went under and problems resulted, made me wish that I had moved it after inspection before concrete)

U value of uninsulated concrete slab and options to improve

Kenny_M — Mon, 19 Aug 2019 11:37:48 +0100

Thanks Tony.

Probably should have been clearer - In this case the slab is already in place with tiles on top. A few people had suggested insulation on top of tiles and dpm between insulation and engineered wood flooring, which was the plan.

As I have noticed a slope on the tiled floor I was considering lifting the tiles - and looked at this 'insulated levelling compound' - https://www.insulationsuperstore.co.uk/product/prooftherm-high-performance-insulating-screed-20kg.html and on that site I happened to notice that their advice was to put down a dpm over the concrete slab, with the insulation on top, to prevent damp rising up and making the insulation wet.

I then took a look at the Green Building Store and their advice is similar to on here, where they are suggesting PUR straight on to slab, but with no dpm and laminate floor floating on top. Not sure if the lack of dpm is because this type of insulation is impermeable.

I can see the argument for both, although my gut tells me that as my slab is above ground level, and the ground outside is not particularly damp, that I am not likely to see much damp coming up the way through the slab.