PIR floor insulation on top of concrete?

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MisterBoy

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The old hothouse I'm restoring into a garden room has a solid concrete floor. The way it's built into a slope, half is a slab on the ground and the other half is suspended (see a couple of photos below.
Internal footprint is ~2.75x5m and I've never used PIR like this before, is it load-bearing sufficiently so I could lay PIR boards and then floor directly on top with laminate or similar? That seems like it could be a big time-saver and also give a nice flat surface but I imagine you probably need at least a sheet of plywood on top, you cannot floor directly onto the PIR foil? I see there are flooring-specific PIR boards, what's the difference are they stronger under compression? I have a stack of regular Kingspan 100mm sheets but presumably these aren't suitable... or for a project like this maybe they are?

I'll point out the very top end of the building, the floor is slightly below ground level, since you step down - probably 1-2 bricks down. There is no sign of damp but then it's well ventilated so that could mask it. Would PIR as subflooring keep any damp in the floor at bay?

edit: trying photos again
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Last edited:
MisterBoy said:
The old hothouse I'm restoring into a garden room has a solid concrete floor. The way it's built into a slope, half is a slab on the ground and the other half is suspended (see a couple of photos below.
Internal footprint is ~2.75x5m and I've never used PIR like this before, is it load-bearing sufficiently so I could lay PIR boards and then floor directly on top with laminate or similar? That seems like it could be a big time-saver and also give a nice flat surface but I imagine you probably need at least a sheet of plywood on top, you cannot floor directly onto the PIR foil? I see there are flooring-specific PIR boards, what's the difference are they stronger under compression? I have a stack of regular Kingspan 100mm sheets but presumably these aren't suitable... or for a project like this maybe they are?

I'll point out the very top end of the building, the floor is slightly below ground level, since you step down - probably 1-2 bricks down. There is no sign of damp but then it's well ventilated so that could mask it. Would PIR as subflooring keep any damp in the floor at bay?



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Click to expand...
You can use PIR for a floating floor, but as you recognise you will need suitable flooring, usually T and G chipboard.
 
Notch7 said:
You can use PIR for a floating floor, but as you recognise you will need suitable flooring, usually T and G chipboard.
Click to expand...
Cheers. For a small project like this, is specific floor pir like ThermaFloor going to make a real difference? Load is just going to be a few people, no heavy furniture
 
MisterBoy said:
Cheers. For a small project like this, is specific floor pir like ThermaFloor going to make a real difference? Load is just going to be a few people, no heavy furniture
Click to expand...
What about laying Celetex, then some 2 x 1 battens at 300 ctrs screwed in place, then some plywood and laminate floor.

If you lay laminate straight over PIR, it would be very bouncy.
 
Thanks @Notch7 I hadn't considered that at all.
It makes sense, but would laying slim joists directly on the concrete be better?
I quite like the idea to keep wood off the concrete just in case of damp
 
Why Not Indeed said:
Look at the specs of the products you are comparing. Compressive strength and U-value.
Click to expand...
Well the PIR products all have thermal conductivity of about 0.02 across the market and when I look at Kingspan therma range, their wall/floor products have the same compression rating of 140 (the roof version is only 100). Their premium Kooltherm floor board is 120 so realistically it seems like they are so similar you could use any if it is resting with full support on concrete and any flooring is likewise well distributed, unless you had some particularly heaving items (like a washing machine or piano).

I never realised that Kooltherm is a different product, not PIR at all?
 
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