DPM, new and old side of extension

5 Jan 2016
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United Kingdom
The things that keep you up late at night!

so today i have been googling lots and of corse end up with varying info as we all do, and i hate making decisions!

i will be breaking my old kitchen floor up this weekend, so i can dig down, lay a new base and put celotex in. all part of a bigger plan for the UFH.

Now, my new side (extension) DPC has "Tails" as i was told they were. basically a foot of DPM sheet hanging out the wall at DPC. so when i lay my new DPM on top of my concrete pad, the DPM tucks under the tails that are in the wall, correct?

that's all well and good, but obviously on my old side of the house the DPM is just turned up the walls and not bedded into the slate bed. obviously because they just did not do it that way back then.

so should i

1- lay the membrane over all of the floor, both new and old. tuck the tails on the new side, and on the old side just bring it up the wall and be done with it


lay a seperate membrane on my new side, all 4 sides lapped, then create an expansion joint and put a seperate DPM on my old side and bring it up the walls like it originally would of been on that side.

i see pro's and cons to both

the buildup plan

screed 50-60mm
UFH (wet)
100mm PIR celotex
100mm concrete pad

i will have questions regards to UFH but il keep that for another night!!
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