Insulating an old concrete floor

[bristolben]

I’m renovating an older house with solid concrete floors which are not insulated.

In rooms where I have carpet, a thick underlay has been just about sufficient.

I am now doing a downstairs main bathroom where I will have 10mm porcelain tile finish.

Is there anything I can put under these (With minimal floor build-up) which would help keep them warmer? E.g. a 6mm XPS board?

thanks!

 

[Deleted member 292770]

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[denso13]

Is there anything I can put under these (With minimal floor build-up) which would help keep them warmer?

Electric underfloor heating mats have minimal build up and would heat them up to a certain extent. The trouble with the uninsulated floor below is that you will lose some heat output downwards.

 

[Donkmeister]

Is there anything I can put under these (With minimal floor build-up) which would help keep them warmer? E.g. a 6mm XPS board?

thanks!

I've done just this - my house has a concrete slab straight onto grade, and the slab was cold as anything. I put either 6 or 10mm XPS (marmox boards, specifically) down in the kitchen, utility and downstairs loo and it made a significant difference in those rooms both to the warmth of the floor underfoot and the general coldness of the rooms. Remember that adding more and more insulation is a law of diminishing returns, so going from nothing to 6 or 10 (sorry I really wish I remembered which!) is more significant than going from 10mm to 20mm.

Two things I'd say are:
1) don't walk directly on the boards after installation - use spreader boards if you have to walk on them at all before tiling. The loading they can actually take is a lot less than the claim in the spec sheet.
2) consider where the bath will be supported by the floor, and cut out just that area of the marmox boards, then fill the gap with concrete. This will obviously make for a cold spot, but at least you know it's solid there and the load is being carried straight to the slab. That might be overkill as I didn't do it under the toilet and have never had an issue, but I did do it under the kitchen units.

But yes, do it - it does make a difference.

 

[Mr Chibs]

Wickes do a similar board to the Marmox type, it’s called sts board, foam inner and a dark cement covering both sides.

Let’s us know how you get on