insulation

Unless there is a wind whistling round the garage and getting into the room, insulating a floor won't make much difference as hot air rises, cold sinks. It's more likely the walls or ceiling of the room have poor insulation - assuming it has adequate heating in the first place.

with reservations, yes.

Yes.

Which ceiling?

Hi both Thanks for the reply. I was thinking to glue the celotex to the ceiling of the garage. This been under the extension floor. The extension has good insulation in the walls and ceiling. My investgation indicate most heat is lost through floor. What kind of adhesive would be best to stick it up with?

Are the ceiling joists of the garage exposed or covered with plasterboard? Is the garage still used as a garage?

Assuming so, then you could use a foil faced PIR board, fixed with expanding foam (dot'n'dab and hold in place with a dead man prop until stuck), and finally tape the joints with ali tape to maintain a vapour barrier.

I'd add a couple of screws per board, as well as the glue, then there's no risk of it falling off one day, you dont need props, and work can proceed without waiting for props to become free. PVA glues al foil, paper and plaster just fine.

NT

Yup, when doing my workshop, I used strips of ply as a "washer" to allow the board to be screwed up. However I could see exactly where the rafters were - might take a bit more measuring and marking on a plasterboard ceiling since you would have to find the joists.

(PU foam goes off well enough to hold a board in 10 - 15 mins anyway)

I guess there must be some reason the OP doesnt want to lift teh floor above and add rockwool etc, it would be far cheaper way to insulate.

NT

Wind in the garage taking away the heat that "flows" from the warm room to the cold garage won't help. But the primary heat loss is due to the temperature gradient across the floor. The floor inside the room is probably at 15C (perhaps more as you say cold air sinks...) the garage at 0C (in winter). A suspened timber floor may have a U value of around 3. Say 10m^2 of floor area, heat loss = 3 * 15 * 10 =

A normal sized garage could be done with 5 boards probably - so £70 including glue etc and a couple of hours work tops. Compared to the hassle of clearing rooms, lifting carpets, and then getting all the floor boards up and back down again, I know which I would choose!

You might also consider draught proofing the garage door/any other door/wndows. BTW I thought there were various fire regulations about cielings of integral garages. Yep. Page 15 here,

One would also assume the existing ceiling (being designed for a garage in the first place) should already meet the required spec. So an extra layer ought not detract from that.

I have the same problem. I've got a temperature sensor in the garage, it's rarely more than 5C above outside temperature. I'd rather not lose height from the garage by installing insulated plasterboard on the ceiling. I also don't want the hassle of taking up the floorboards of the room above to install rockwool.

Does anyone know of any DIYable insulation that could be inserted in through holes drilled in the chipboard floorboards above? I'm thinking of something like packing peanuts and a garden blower. A google search hasn't revealled anything yet.

You can do that using polystyreene beads. And since there's no potential for damp tracking, you can also use shredded polystyrene, which is cheaper. Do make sure there's no exit hole anywhere first, or the beads get everywhere. Of course once you've drillled a 2" hole every joist spacing you've then got to block them all, so its arguable how much hassle you've saved.

NT

ote:

Yeah. Last time I accessed a floor structure over a garage, teh chip just lifted up.

NT

Cut a strip or strips out of the plasterboard ceiling, poke in rockwool with a stick and replace the strips.

The OPs method will also not affect the installation methods of any cables under the floor. Covering a 2.5 T&E with insulation would mean that it would not be suitable for a 32A ring circuit.

I'd be concerned about flammability issues, sticking Celotex to the ceiling of an integral garage. Should I be?

(My interest is more than academic - I have exactly the same issue. Our bedroom is over the integral garage, and it's cold ...

The PIR foam itself is not a fire risk, in the sense that it is treated with flame retardants, and is self extinguishing - in fact it usually has a class 0 fire rating (i.e. very good).

I did read of some concerns when large areas are fully[1] enclosed in high performance insulation which does not have another covering over it. Apparently, the thermally reflective nature means that in the event of a fire, the room temperature can rise much faster than it would otherwise. Covering with plasterboard etc is supposed to mitigate that risk.