Floor insulation for underfloor heating

[Derbylad]

Hi All,

I have a bungalow with solid concrete floors which I assume have no insulation as it was built in the 70's. I will be removing the roof and adding new roof trusses to create a second floor. Whilst replacing the roof I plan to increase the ground floor ceiling height to allow for extra ground floor insulation and underfloor heating.
I would like to supply the heat through an air source heat pump.

What would you recommend is the best floor insulation system/best insulation value for thickness?

Which underfloor heating system would you recommend and why eg Nu Heat?

Has anyone undertook a renovation of this type?

Cheers

 

[muggles]

If you're planning an ASHP you need a LOT of insulation - you will probably need to consider exterior insulation on the walls as well (and at the very least, cavity wall insulation and new windows) to bring them up to sufficient levels for ASHP to work. A badly insulated property will chew up an enormous amount of electricity boosting the heat pump, negating both the savings in running costs and carbon emissions.

Best insulation value for thickness as far as floor coverings go is AeroGel Thermaslim IFI, which has almost twice the insulating properties of the same thickness of Celotex, but is much more than twice the price. An 8×4 sheet with a 50mm height build (which is what you'd need) is about £600. If you can dig down 8" and insulate the floor in the more traditional manner, that would be much cheaper (albeit messier) and you could then have a traditional pipe-in-screed system

If you are going to go for an overlay system, NuHeat LoPro Max gives the best thermal output per square metre. NuHeat also offer insurance-backed guarantees that the system they specify will actually heat your home to an adequate level, and they do all the design calculations for you. As I said though, pipe in screed is your best option if you're prepared to do some digging. Alternatively, as you're also intending to add a second floor, which might require your foundations to be beefed up, have you considered simply knocking the place down and starting again? By the time you've increased wall insulation, excavated the floor and added insulation, and underpinned the property, it may well actually be a very similar price to simply demolish and rebuild

 

[endecotp]

Best insulation value for thickness as far as floor coverings go is AeroGel Thermaslim IFI, which has almost twice the insulating properties of the same thickness of Celotex, but is much more than twice the price. An 8×4 sheet with a 50mm height build (which is what you'd need) is about £600.

On the subject of crazy-expensive insulation, I noticed that Insulation Superstore now seem to stock vacuum insulation panels at prices that are not quite as insane as they used to be. VIPs are significantly better insulators than aerogel; aerogel is around 0.014 W/mK, while VIPs are certified as 0.008 W/mK. 30mm panels seem to cost about £100 per m2, which is half your aerogel price (but doesn't include the hard MgO facing). I think the only convincing application for aerogel is when you must have something that's vapour-permeable.

More practially, Seconds & Co have 75mm Kooltherm phenolic insulation boards (0.018 W/mK) for about £15 per m2, IIRC.

 

[Derbylad]

Thank you both for your responses.
Bit of an eye opener on the cost of floor insulation! My bungalow currently has a footprint of 90m2. Unless my math is wrong, the Aerogel would cost £12.5k! ouch. Couldn't find anyone selling it on the web though.
The Kooltherm is a great price at Seconds&Co so will definitely price check with this company if I go for a retrofit. I cant see that the odd dent in the board would compromise its performance!?

Digging the floor out is definitely an option, although I'm not sure of the cost. But the cost could be mitigated against a lower cost on the underfloor heating.

I am starting to wonder if demolition might be the best way forward though. I would be able to save on the VAT....I think!? Would any one know if I could claim the VAT back if I retain a detached double garage on the site?

I have been told that it would cost circe £10k to demolish and clear. Does that sound about right for a 90m2 bungalow?

 

[Doggit]

As it's more than likely that the door thresholds aren't that deep, so adding insulation would put the new floor higher than the door. If you keep the existing house, then digging down may be a necessity, but if your foundations are a raft design, then you couldn't do that, but is should mean they are strong enough for an upper storey. and is the house in a Radon area.

You need an SE to ascertain if the foundations are okay, and I'm surprised this hasn't been done yet, but if the foundations are good, then it might be worth looking at removing the doors etc and lifting them a couple of courses and then putting in the insulation.