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Perimeter insulation for heated slab - roll or EPS board?


oranjeboom

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Just getting my final orders in before I start to lay my insulation down and just checked what my UFH supplier was going to provide in terms of perimeter insulation - it's only 8mm thick! I understand it's on a roll and therefore can't be too thick, but this seems very thin.

 

I am tempted to go with this technique that @JamieM describes here :

 

Surely 25mm EPS offers better u-values?  And using the wedge technique described in the post would provide a more robust approach I would think too? I can imagine that some of the perimeter rolls are not always ideal when sticking in dusty environments.

 

I guess on most installs the perimeter roll insulation is a nice quick solution, but prone to movement during installation of ufh or pouring of concrete (concrete/screed could force a gap between the upstand and the insulation board below causing a thermal bridge with the adjacent wall).

 

 

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The 8mm on a roll is flexible insulation to allow the slab to expand and contact. It's not really for thermal preformance. I put in 40mm insulation and then the flexible roll. That matches my service cavity so you don't see it as I've a polished slab and didn't want it seen. Put in whatever fits for you.

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I did exactly the same as dudda.  You can always tape the stuff.  I still dont understand why they give you so much of the stuff though - we had rolls of it left over.

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Thanks. Yes, I had realised that the roll-type was more for compression purposes. I'd just noticed that on some UFH details / slab details, it was either a case of proper 25mm+ upstands or the thin perimeter roll type upstands. I suspect that there are a lot of slabs with just the latter.

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I put an 40-50mm EPS upstand around the edge. Thicker in some places as the room was about 3"off square and there was an old doorway to bridge etc. It wasn't straightforward as there were footings I'd squared off to go around. I would hold the upstand in place and square with a board and a few blocks then use low expansion gun foam to hold in place.  My DPM went over the 25mm EPS on the floor.

 

SAM_1633

 

150mm PIR onto the DPM, spray glued where it comes up against the EPS upstand. Then expansion strip on a roll that was like corrugated cardboard with an EPS backing.

 

SAM_3091

 

It has sort of a pre fold in it and it sticks down to the foil. There's another self adhesive strip on top if you have a membrane between foil and screed/concrete.

 

SAM_3093

 

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Thanks Onoff! Looks like I need to get some spray glue and some low expansion tape, as parts of the old bungalow retrofit I have footings everywhere that will need filling/securing with bits of insulation / upstand. So you ended up with a 25mm EPS layer on top of your celotex? Was that simply to get to the correct height? I just started another post on that very subject.

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