Insulating the slab for underfloor heating

21 Feb 2010
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West Glamorgan
United Kingdom
Hi All,
I'm in the process of constructing the slab foundations prior to pouring the concrete for a kitchen extension.
I'm planning on installing wet underfloor heating and looking for the best way of insulating the slab.
My architect has drawn the slab as such, from kitchen floor down:
Screed, insulating bats,DPM, sand, concrete, harcore, ground.
My builder mate who's helping me insists he's always put slabs in as follows:
Screed, DPM, concrete, insulating bats, sand, hardcore, ground.
Local building reg's officer does'nt mind either way???

I'm of the opinion that with a layer of insulation before the concrete slab the UFH will be more efficient? So better the architect's way ?

Its a battle of wits at the moment. :LOL:

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Your architect is right(strangely enough)

ontop of your membrane you want your celetex,to which you fix your ufh pipe and then screed ontop.max screed is about 70mm but they manufacturer a specialist fibre screed for ufh which holds the heat far better.
The insulation should be above the membrane for obvious reasons. The membrane should be sitting on sand, again for obvious reasons. So I think your builder isn't quite ready to qualify as an architect yet ;)

Your architect's approach is sound although personally I prefer the concrete on top of the insulation. Nothing wrong with extra thermal mass inside the insulation. Unless you're building a warehouse, the edge insulation is the most important part anyway. There's good reason to think that slab insulation is pointless if the edges are insulated well enough.

Anyway, there's nothing wrong with what your architects specced so I think you have to go with that. He's got all the details and he's the one you'll be complaining to when it doesn't work :LOL:

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