Underfloor Insulation - Composite Materials Any More Effective?

gaelicyoda

Hi All,

Got a question regarding underfloor insulation:

Say I have 150mm to fill between my sub floor and my finished floor levels, and I want to put in underfloor heating, advice tells me I should split the height 50/50 - i.e. 75mm insulation and 75mm screed.

Now, would my 75mm be best spent putting in a solid 75mm thick of Kingspan Kooltherm K3 Floorboard insulation (is this the most efficient foam insulation by the way?) and then the screed, OR might a better setup be (putting aside an extra 2mm for the moment) to put in 70mm instead and then on top of that add 7mm foil laminate insulation (airflex I think it's called, or a similar technology)?

I think I read somewhere that this insulation is supposed to work reasonably well in tandem with another, and particularly underfloor heating.

What do the good folks on boards think about this alternative?

Basically, I want to queeze the most efficient insulation into this 75mm, the thinner the better since ideally I would have more height to work with to achieve a good u-value, so any comments people have are most welcome.

Cheers,
GY.

holdfast

no go for 75mm Kingspan.

gaelicyoda

Thanks holdfast.

PJMCKE

Are you sure 75mm of kingspan will make the required regulations in terms of U values. I would check this out as you may find that you might need more insulation. It relates to the perimiter to area ratio. 75mm should make regulations of 0.18 but if you are going with underfloor heating you will come up short with 75mm. Check it out first.

ardara1

You have to achieve 0.15 of a U-value - you'll not get that with 75mm of Kingspan Phenolic. Ask them for the equivalent in Therma boards - 40% cheaper and only about 5mm thicker. Foiled board DON'T work under concrete - use Bacofoil instead - same performance

gaelicyoda

Thanks for you replies folks - I should have said, the planning permission for the house I'm looking at is old, in fact the guy who built it only did so before the permission ran out - so the house has been built to 2002 building regs. (as ammended).

I'm basically just shooting for the best I can get, but there shouldn't actually be any legal implications.

holdfast

The reason the regs are there are too ensure you are not heating the ground under the house. I guess who ever is signing off the house would like to know if your going with underflooor and only going with 75mm insulation. Have you check the sub floor for insulation below it. It is hard to comment on your build when you have not seen it and may miss the original design concept and give you bad advice.

gaelicyoda

Thanks holdfast - yes, that's pretty much what I'm shooting for. The more effective an insulation I can fit into the 75mm the better. Don't want to be wasting expensive heat just to heat the ground!

As I understand it, if I wanted to go for any more than 75mm insulation though I'd have to either; (1) Raise the floor level to accommodate the extra insulation, and consequently the door heights of all the internal doors or (2) reduce the amount of screed being used which would reduce the thermal mass and therefore would cool quicker once the heat is switched off (although, it would have a quicker response time).

Good point about the subfloor insulation, but I was advised to pretty much ignore any subfloor insulation because unless it is brought up around the sides of the subfloor as well, there will be a thermal bridge through the sides of it, rendering it pretty much useless.

YourAverageJoe

ardara1 wrote: »

You have to achieve 0.15 of a U-value - you'll not get that with 75mm of Kingspan Phenolic. Ask them for the equivalent in Therma boards - 40% cheaper and only about 5mm thicker. Foiled board DON'T work under concrete - use Bacofoil instead - same performance

what is the difference between kooltherm and therma board