Floor Insulation

[Gillesa]

I'm at the stage of my extension where I need to lay the floor insulation before doing the screed.

I currently have a concrete slab, which will have a DPM, then 100mm of PIR. The issue I have is that when I did the concrete slab, I didn't manage to get the surface completely flat. I could do with filling any voids under each insulation board so that it is fully supported.

I was originally planning on putting a thin layer of sand down, but because I don't want to increase the floor level any more, this would need to be extremely thin in places, and compacting this with a wacker onto a concrete slab might be a bit aggressive.

I was wondering if it is possible to stick each insulation board down with expanding foam adhesive, as I have done with the roof. This would fill any gaps and be much easier for me to do, but will this provide suitable support for the floor? I would think as long as I apply a decent amount then this should work, but can anyone suggest a reason why this is a bad idea?

Cheers.

 

[matlob]

Bit late now but I think the insulation usually goes under the slab.

You could try some self levelling to get the worst of the ditches out

 

[noseall]

I'm at the stage of my extension where I need to lay the floor insulation before doing the screed.

I currently have a concrete slab, which will have a DPM, then 100mm of PIR. The issue I have is that when I did the concrete slab, I didn't manage to get the surface completely flat. I could do with filling any voids under each insulation board so that it is fully supported.

I was originally planning on putting a thin layer of sand down, but because I don't want to increase the floor level any more, this would need to be extremely thin in places, and compacting this with a wacker onto a concrete slab might be a bit aggressive.

I was wondering if it is possible to stick each insulation board down with expanding foam adhesive, as I have done with the roof. This would fill any gaps and be much easier for me to do, but will this provide suitable support for the floor? I would think as long as I apply a decent amount then this should work, but can anyone suggest a reason why this is a bad idea?

Cheers.

You dont need to compact the sand. Plus, the sheets themselves usually have a wee bit of 'memory', meaning they rarely sit flat.
Just use building sand to fluff out any pockets.

 

[SpecialK]

I used small amounts of sand to fill in the dips on the concrete floor and worried a bit about the insulation moving. Once it's got the weight of the screed on ... it won't go anywhere.

 

[Gillesa]

Thanks for the advice guys, I'll see how I get on with the sand.