Floor Insulation

[newinvention]

I'm renovating an old stone cottage. Have laid a concrete base over a DPM. I want to finish with laying tiles and have 1 1/2" left to play with. Can anyone recommend a slim, effective insulation that tiles can be laid on? Simon

 

[FamilyWiggs]

I used FastWarm sheet insulation underneat electric underfloor heating.

Laid it directly onto sand on top of concrete (I know, but it was already there!). Laid UFH into screed on top, and laid flags directly onto screed. Works a treat. Can be purchased in varying thicknesses.

There are many suppliers and similar makes. Prices can vary a lot, so pays to shop around. The following site is one of the first I Googled - not necessarily the cheapest:

http://www.floorheating.ltd.uk/fastwarm-technical-information.php

Cheers

Robin

 

[Schoolmarm]

Have laid a concrete base over a DPM.

:shock:



Aaaah, so you need advice on the best way to dig this concrete up? Ok well it should be a little easier if it is laid on plastic.

 

[MdB]

Concrete floors over DPM in an old building is often a bad move as although you get a nice dry floor, it makes the ground under the DPM wetter as the moisture can't evaporate. This can make the bottom of your walls damp.

Having said all of that, we have just had a large amount of concrete with DPM laid in our house as about 80% of the walls are modern and we were able to link in the DPM through the walls. We also left a foot gap next to all the old walls which will be filled with insulated limecrete to allow at least some of the moisture to evaporate.

Back to your original question, tiles I would have thought need to be laid on something really quite solid so a layer of Celotex or similar is really ruled out. It would have gone nice under the concrete though, though I guess this is a little late now.

 

[AMc]

Have you got BC approval for the renovation?

I'm puzzled that you've not considered insulation before - I thought insulation in the floor to building regulations was a required component as you were 'renewing' the 'thermal element' - not saying I'm sure but I was under the impression that as soon as you fiddled with more than 25% of an element it had to conform (listed buildings aside).

 

[shelli]

when we did our nasty floor (i.e poured concrete ) we poured the offending stuff onto kingspan which was sat on top of the DPM - we had to dig down 9 inches to get enough room to do this as ceiling is only 7 feet high. apparently this insulates your room from the world beneath - We certainly received advice from Building control that in order to meet building regulations we had to have a thermal element in the new floor - but perhaps Simon can get round this and has been canny enough to avoid endless digging by thinking that an underfloor heating system will work just as well and will probably comply.

My only question would be how good a thermal insulator is the actual concrete(? engineer please - I have no idea) and what is concrete sitting on? - if theres only the DPM and concrete between the heating elements and the underworld won't a lot of his heat be lost downwards?

Shelli X

 

[Penners]

All other aspects of this aside, if you have only about 37mm to play with I think I would have concerns about laying tiles on top of an insulation material, even if you managed to squeeze a thin concrete screed over the top of your insulation.

By its nature, insulation material such as Celotex or similar has an element of "give" in it, and I therefore suspect that your tiles will suffer from movement. This could crack the grouting and possibly cause failure of the adhesive over time.

 

[Gervase]

It's certainly normal to put insulation under the slab if you're using concrete - usually four inches of Kingspan or Jablite or some such polymer. The new Part L Building Regs are very particular about thermal performance, and most BCOs will want to see evidence of insulation under the slab.

Many plumbers will now also put an insulated foil-faced sheet under the UFH coil on top of the slab to ensure most of the energy goes into warming the screed above and not the slab below. That does need a thicker screed, though - I have seen a 50mm screed laid onto the insulated sheet which had cracked. You only need a millimetre of so of deformation under a thin screed to risk cracking - so I'd say a 75mm screed would be the minimum in this case. As Penners says, I'd worry greatly about tiles cracking and moving if you were to put any effective insulation under them without that sort of support.

 

[MdB]

Our new floor is 100mm concrete, 100mm celotex, underfloor pipes and then 70mm of screed. Underfloor heating people said a minimum of 65mm for the screed.