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Insulation Thickness for Retrofit wet Underfloor Heating

Postby J2020 » Tue Jan 14, 2020 10:14 pm

Hi. I have a 1970's house.
Built on a concrete raft because coal mining area.

It's currently gutted back to brick (long story).

I want to get a wet underfloor heating system installed in 3 of the 4 down stairs rooms.

Looking at the edge of the floor (where some of the concrete screed has broken away) I can see a plastic damp proof sheet sticking up, and what looks to be about 50 mm of concrete laid on top.
I think that is all there is on top of the raft.

Currently I have about another 30 or 40 mm spare up to the height of the threshold of the front door.

So, I've got about 90 mm to play with.

I was thinking... Take up the concrete screed.
Lay new dpm if I damage the old one in the process...
Then lay 25 mm of kingspan (or equivalent) insulation...
Clip the heating hose down...
35 mm self level screed over the top...
And then un-graded lime stone floor over the top of that. (15-25 mm thick, plus muck)

Total 90 mm thick.
Taking me up to the level of the front door threshold.

My question (finally) is this;
Will this be ok BR wise?
I saw somewhere that insulation must be a certain U-value or something.
But, my point is I don't have any insulation right now.
So, 25 mm is better than nothing! Right?

Comment / questions / suggestions,
Thanks in advance.
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