Insulating an integral garage ceiling

[David J]

I haven't seen this problem addressed here before, but it must have been....?

I have a 1997 built detached house with an integral garage and a small bedroom located over the garage. Last year the entire house outer wall cavities were filled with glass fibre insulation (via holes) but this has still left me with an unheated garage and two uninsulated surfaces of the house: the garage ceiling and the adjacent house wall. I have a plan for the wall and I'm now thinking of a solution to the ceiling problem.

I'm sure that there is no insulation between the floorboards and the garage ceiling, but I do wonder what the building regs say about living quarters over a garage that also is the home to the gas-fired c/h boiler? A fire-proof barrier?

My idea for the ceiling problem is to fabricate a crude false ceiling about 200mm beneath the existing one, using MDF 2400 x 1200 x 9mm panels as the surface. These to be supported by about five 38 x 63mm studwork timbers attached to the garage walls using joist hangers.

I would then stuff the void with 100mm loft insulation, working as I progress along installing the MDF panels.

Can anyone see any problems here?

David

[Huge]

Yes. Integral garage ceilings have to be constructed of non-inflammable materials. Two layers of 12mm plasterboard suffice, but I'm pretty sure MDF isn't allowed.

[Andy Dingley]

Sort of. You can use Viroc's Versapanel for this. Cement-based enough to meet the fire retardance requirement, but also near enough the strength of MDF, rather than plasterboard. Handy stuff, as it's pretty weatherproof too, although the thinner boards are annoyingly brittle.

[John Rumm]

The boiler is not really relevant (after all they are often in rooms of a house with no special fire break protection from others). However the garage ought to have at least a couple of layers of plasterboard on its ceiling.

Seems like more work than is necessary. Could you either:

lift the floor in the room above and stuff the void with insulation, or screw an insulation backed plasterboard to the garage ceiling under the existing one. If you want really quick and cheap, stick some PIR foil faced foam boards to the garage ceiling and don't even bother with a lining.

[spamlet]

Can't you just put loft insulation under the bedroom's floorboards?

S

[David J]

No floorboards in modern houses... Very large panels nowadays sadly.

David

[spamlet]

But power screwdrivers too: don't you have services under those boards you may need to get at sometimes?

Otherwise: small hole + expanding foam/ cavity wall insulation?

S

[pcb1962]

And you also want intumescent sealant (

around the edges and the joints.

[David J]

Thanks to all for the responses...

I think I'll go for this last suggestion of Johns for the ceiling and the wall. My nearby Travis Perkins stock Xtratherm Thin R PIR 8ft x

4ft panels in various thicknesses that look right for the job. The counter guys there reckon that woodscrews will hold it OK to the existing ceiling plasterboard.

David

[John Rumm]

If you get long PB screws, and aim for the joists you will only need a few to tack it in place. A few dabs of expanding foam or spray on contact adhesive (on both surfaces) would help.

[David J]

Thanks - I'll look into your contact adhesive idea. I was wondering how to hold the panels in situ (on my own) while getting the screws in.

Any tips on locating the floor joists here? Are they a fixed distance apart? The plasterer has done an excellent job and all I can see is a smooth pink surface.

Tapping the surface? Metal detector for the nails possibly?

David

[John Rumm]

said that, with impact glue, there is no holding til it sets - since you let it dry mostly before putting it up, and then it has instant grab.

Yup they will be on regular spacings - usually 400mm.

A few options:

A stud finder may help. If not, the metal detector function of the stud finders will find the existing nails and screws.

In the absence of a detector a strong magnet will also find the nails/screws

Tapping can work - but its harder if there are a couple of layers of plasterboard.

[spamlet]

A compass, should find the screws/nails and electrics too.

S