Garage conversion - new floor

bluewater

Planning to convert integral garage to habitable room. Have builder ready to start in August. To comply with building regs the existing concrete floor must be removed and a new one made. We will have electric underfloor heating under engineered wood (or possibly bamboo). So new floor would be concrete first, then 100mm celotex, then DPM, then screed (possibly liquid screed).

Went to the Homebuilding and Renovating show at Sandown a week or two back and spoke to underfloor heating people (wet - not what we are planning) and one said that instead of concrete under the celotex you could used type one. Obviously it will be up to the building inspector to say what is permissible but wondered whether anyone has heard of this and whether it is likely to be permitted.
One reason I'm interested is that it isn't easy to get close to the site with a premix lorry and it's quite a big area.

bluewater

Just looked at the Celotex website and it says you could put tongue and groove chipboard on top of the insulation instead of a screed.

ComicGeek

bluewater wrote: »

To comply with building regs the existing concrete floor must be removed and a new one made.

Who says? Why can't you use the existing concrete floor and insulate over?

If you're struggling with levels between the garage and the rest of the house then you could reduce the insulation thickness, but depends if you're in England, Wales or Scotland.

bluewater

Knocking through from kitchen and floors are the same level now so to keep the same level, have no option (England)

ComicGeek

But have you checked that you can't offset the lack of floor insulation against increased wall/roof insulation? Just might be a much cheaper option than digging up and relaying the floor. With an integral garage the perimeter/area ratio might be ok.

Does the kitchen have insulation in the floor? Seems strange that they are the same height, so suggests that it doesn't.

bluewater

House built in 1953. Kitchen floor is tiled and plan to remove these and replace with engineered wood (Bamboo) with underfloor heating.
The integral garage has a rear extension - mostly single skin so internal insulation (warm batten method) required.

Would be great not to have to dig up the floor but can't tolerate a step up. Obviously no idea how much concrete there is.

bluewater

The new kitchen floor will raise the height a bit - maybe 20mm but have to keep same level as hall etc.

Will check perimeter ratio

ComicGeek

So the garage is only exposed on 2 sides? Given that you don't have any existing insulation in the floor in the other parts, I would definitely argue that you can't install insulation in the garage due to internal levels. Even if you have to install more insulation on the walls internally or roof to compensate. Digging up the whole floor sounds crazy.

You would still need insulation mats beneath the electric heating mats to stop the heat just disappearing straight down into the ground, but this would normally only be 6-12mm. Worth working out what system you want to use and work out overall depths for both the kitchen and garage.