Sub floor in kitchen

mordzy · 2 Sep 2019

My kitchen floor has always been about 6" higher than the rest of the ground floor. Its always annoyed me so ive taken the kitchen out and dug it up. Ive removed about two tile layers between cement screeds so presumably its just been added to over the years. Ive got down to soil now which is great.

My question is, do i need a slab pouring before insulation? I was wondering if i could just hardcore and whacker plate, then visqueeen, insulation and finally to top screed for the finished floor.

Thanks.

23vc · 2 Sep 2019

Pretty sure you still need the structural slab.

Mr Chibs · 2 Sep 2019

How much room do you now have to 'make up' to get the floors level?

Sounds like you won't have enough height to add all the layers, sand blinding, insulation, slab, screed etc.

mordzy · 2 Sep 2019

I can keep going down, its just labour intensive. I was going to go with the 100mm kingspan i have left over from another job. So that sat on a visqueen sheet with a screed slab (approx 120mm) on top. Ill have to go deeper if i need a slab on dirt.

^woody^ · 2 Sep 2019

Whilst it seems like an old house and the ground solid, with no problems with the existing floor, your idea may well be viable, but the risk of uneven movement at some future time, or resistance to movement as a result of external influence (say raised or reduced ground moisture levels) would be greater.

Leofric · 2 Sep 2019

you can put the insulation above or below the concrete slab - if above , screed on separating layer /vapour barrier on insulation on concrete slab on sand blinding on hardcore.

mordzy · 3 Sep 2019

Ah didnt realise i could do the insulation below the conc slab. What could i sit this on? just hardcore.

I thought i would have to do from the bottom up;

hardcore
sand binder
visqueen
concrete
insulation
visqueen
screed
floor finish

are you saying i can do;

hardcore
insulation (celotex)
visqueen
concrete slab
floor finish

My concern was that the foil of the insulation would perforate and deteriorate the foam if it was sat on the ground

23vc · 3 Sep 2019

mordzy said:
hardcore
insulation (celotex)
visqueen
concrete slab
floor finish

That’s what I did, all good. I also blinded the hardcore with sand.
Insulation on top of the DPM is also common, but BCO on my latest one steered me towards the above.
Don’t forget perimeter insulation.

^woody^ · 3 Sep 2019

The problem with putting PIR under the slab is that you loose some of the efficiency, due to the slab needing to be be heated up before the insulation starts to work. The insulation really needs to be as close to the room as possible.

23vc · 3 Sep 2019

Didn’t have a screed tho so not sure I could have done that

Leofric · 3 Sep 2019

Sorry, I should have said

Leofric said:
if above , screed on separating layer /vapour barrier on insulation on concrete slab on dpm on sand blinding on hardcore.

65mm screed, 500g polythene separation layer, 125mm Kingspan Kooltherm K3 insulation, 25mm perimeter edge insulation. 100mm thick C30 grade concrete floor slab, 1200 gauge polythene dpm taken up edge of slab and lapped with horizontal dpc. 50mm sand blinding on 150mm well consolidated sulphate free hardcore or as engineer’s recommendations. Max ‘U’ value 0.13 w/m²k. - this is a typical specification.

Mr Chibs · 4 Sep 2019

Out of curiosity, is this a standard spec for a concrete floor, I’m debating laying one at the moment, from your spec I’d need to dig down around .5m from finished floor level... does this seem about right?

Leofric · 4 Sep 2019

Mr Chibs said:
Out of curiosity, is this a standard spec for a concrete floor

Leofric said:
this is a typical specification.

Mr Chibs said:
from your spec I’d need to dig down around .5m from finished floor level... does this seem about right?

can't explain it any better than I have already done with the typical specification

Leofric · 5 Sep 2019

Mr Chibs said:
Out of curiosity, is this a standard spec for a concrete floor

Perhaps I can explain it a bit better, it is actually a genuine (not copied from some internet site ) building regs approved spec I wrote for an insulated ground bearing floor for a real house. When used several times I suppose it becomes 'standard'.

geraldthehamster · 5 Sep 2019

How about

Hardcore
Sand blinding
DPM
Insulation
120mm concrete with mesh fabric chucked in for good measure?

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Sub floor in kitchen

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