Sub-base & insulation for new concrete floor

[Graham Kay]

Hi

I am prepping for two new concrete slabs in the kitchen and utility (12m² + 6m²) of a Victorian house to replace stone flags over bare earth. Following builder's advice I've dug it all out to 300mm (+/-20mm).

• What's to choose between the many various types/brands of insulation board?!
• In terms of the sub-base/crusher, is MOT type 1 the best stuff to go for (hiring a small whacker)? What's there right now is bare earth, bits of brick, rubble etc.

Build-up will be (correct me if wrong!):

1. 50/75mm crusher
2. 25mm sand blinding
3. Visqueen
4. 50/75mm insulation
5. Vapour barrier(?)
6. 100mm concrete
7. Levelling screed
8. Flooring (undecided)

Cheers in advance!

 

[Notch7]

Does it fall, under building regs?

If so, you will need a certain thickness of insulation.

 

[John D v2.0]

I'm not sure 50mm of mot would do anything, as far as i knew 100mm is the minimum to do anything useful.

 

[Graham Kay]

Thanks for the responses.

Does it fall, under building regs?

If so, you will need a certain thickness of insulation.

Yes, I've checked with the building inspector already (when he was round to look at something else) and used the Kingspan calculator.

I'm not sure 50mm of mot would do anything, as far as i knew 100mm is the minimum to do anything useful.

That makes sense. I've got some leeway with the insulation (was going for more than necessary), so there's room for more aggregates. Save some ££ that way too, eh?

 

[Leofric]

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 other measures as engineer’s recommendations. Max ‘U’ value 0.13 w/m²k.

 

[Graham Kay]

Hwæt, Leofric. Thanks for this info.

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 other measures as engineer’s recommendations. Max ‘U’ value 0.13 w/m²k.

By my reckoning that's 515mm in total. Really don't want another 2 days digging and don't need quite such virtuous U value. Can I get more like 0.22-0.25 w/m²k with the 300mm depth I have?
Thanks again.

 

[Leofric]

Omit screed , power float finish concrete, put insulation under slab, reduce thickness of insulation and sand blinding -
so 100 concrete on vapour check/separating layer on 75 insulation on Visqueen 1200 dpm on 25mm sand blinding on 150 hardcore.
Total thickness 350mm.
Email spec and room dimensions to Kingspan technical department & ask for U value calculation for this ,and recommendation for thickness of insulation around edge of slab ,or minimum thickness insulation required to achieve U value of 0.22.
You might also ask if they advise a separate vapour check/separation layer.

 

[cAtLeYx]

Leofric is spot on with the make up and the sequencing. Typical floor insulation in modern construction is typically 75mm. Kingspan can advise further. Have you considered a suspended timber floor...?