Celotex, screed and underfloor heating

9 May 2011
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United Kingdom
I've just built the extension and still have a concrete sub floor upon which I need to put in our finished floor. The finished floor will comprise of 100mm of Celotex with an underfloor water heating system which is pinned to the insulation and then covered in a screed of around 80-100mm.

The walls are block with a cavity and 80mm celotex in the cavity.

My question is regarding the laying down of the celotex and in particular the edging, where the celotex meets the wall.

I understand that its good practice to place celotex upturned around the perimeter which comes to the height of the finished screeded surface and is therefore higher than the flat laid celotex. Can I use the same 100mm celotex to do this? Or should I used something a little thinner like 50 or 80mm?

Any help/advice greatly appreciated!
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