Concrete Floor Insulation

[aturner]

Hi All,

We've got a 1994 David Wilson detached property. We're extending the kitchen at the rear and want to have Wet Under Floor Heating in the new and the old part. How do I decide if the existing concrete floor has insulation already in the slab. The house is built on a raft foundation.
I've searched this forum for hours but have been unable to find anything similar.
I would really appreciate any advice anyone could offer.

Thanks in anticipation.

 

[b1llt]

Contact the developer see if it was part of the spec. If not then either drill a 50mm core hole, bearing in mind you'll probably puncture the dpm - no biggy though. One thing I often do is drill tight to an existing wall to see if any insulation has been brought up the sides ie 100mm rip, if that's there then most probably you have insulation in the floor. Other than that its a core hole, or when you extend then hit into the side of the structure and take a nose, again the problem especially with a raft could be its got a toe and then you'll see nothing, but if its a suspended slab ie suspended on the inner skin then you can core out and get a good cross section.

Bottom line the only way to know another than trying to do crazy calcs is to physically look. Hopefully you got 100mm insulation, 100mm suspended slab with dpm and a393 mesh - sweet if so

For your new slab defo c40 (its a cheap as c35) concrete, 100 to 150 insulation I like kingspan (encon or sheffield insulation are cheapest) sand blind then dpm, then insulation, then tape it all, then return the insulation up the sides 50mm wide is plenty, then another dpm, then chairs then a393mesh (keyline burdens etc) then concrete - leave 50-60mm for screed and use a fibre screed. Doing my kitchen as we speak for that very reason no insulation or dpm.

Dig, sand blind 15mm, dpm, insulation, insulate sides, tape, dpm, chairs, mesh, concrete, heating, fibre screed

Hope that helps.

 

[aturner]

Hi b1llt,
Many thanks for the info. David Wilson were taken over by Barrats some time ago and when I contacted them, they said the original spec and plans would have been destroyed. They didn't seem keen to help at all. Tried looking at the 1991 build regs to see what the spec was at that time but not much help there. I think you're idea of a test hole might be the way to go. Am assuming the insulation should be reached before the DPM but if I do puncture it any suggestions on what to seal it with.
Kind regards

 

[b1llt]

It may have insulation we were putting it in back then and before that. The dpm could be above or below, I'd not fret over a 50mm core, just cut some dpm ie plastic use a thick bag put it in the hole and so its like a pocket and fill, you could put resin in. What I do is after cutting the screed away tape around the core cutting bit at 90mm core to that (then take the core bit out, and hit the center of the cut concrete with a lump hammer, not to mental its a feel thing, put the core back in and give it a quick spin and the core will 9 times out of 10 snap and then you lift it clean out and it doesnt damage any dpm - not always, but if the force is with you then it does

Back then more often than not it was put above the dpm so that the chemicals in the deck did not damage the insulation Have fun and its nothing you'd can't repair with ease