26 Mar 2020
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United Kingdom
I have a timber frame structure mounted on concrete blocks around the perimeter, which are bedded on a concrete base.The concrete base has a membrane but is cut off flush.
as i'm doing a solid floor inc Ufh made up of 150mm celotex , a seperation layer then UFH stapled on top , before a 75mm screed to finish should I :
Also Put polythene down before the celotex as well so it can drape up around the edge meeting the damp course above the concrete block level ??

see image
annexe  dpm.jpg
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Any membrane needs to be continuous with any DPC so as to form a complete barrier under the floor and up the walls at ground level
You could also do with some celotex 25mm or more applied to the Perminter walls (like skirting boards) This will stop any cold bridging.

From your ground level up to top of screed.
Yes I'm aware of what should have been done, BUT as it is now , can i rectify by adding additional polythene under the celotex too ??????

Im just concerned if that would have any affect. I intend to put insulation around the perimeter 'skirting board style' to combat bridging

see modified picture , intending to put polythene (dotted line ) in underneath celotex
annexe dpc 2.jpg
as well
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Is there a DPM under the current slab?

If it was me, I would put a DPM down On top of slab and fold up the sides, perimeter insulation, floor insulation, Polythene sheet, then Carry on with UFH.

As you said you can do what you have already. When retrofitting a concrete floor, you don’t have the luxury of lapping the DPM into the walls.
Thanks Guys, Yes there a dpm under the new concrete slab (2 yrs old) but the laps cut off, but i guess if i do above its bolt n braces

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