garage ceiling insulation

28 Nov 2007
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United Kingdom
Hi! I have an integral garage. The rooms above were v cold, so I insulated between the joists (approx 10cm thick roll) from below and had the garage ceiling plastered. Despite this and already having cavity wall insulation, the rooms above the garage are still v cold. I am trying to decide between having a suspended ceiling fitted in the garage and laying more insulation above this or fixing Kingspan boards approx 4cm thick to the plastered ceiling using 'No More Nails Ultra'. Does anyone see any problems with either of these two solutions? Thanks!
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Heat rises, so any heat in the rooms above the garage will be going out through the ceiling, not dropping through into the garage. It's your roof insulation that needs upgrading.
What you have done in the garage so far should be adequate, unless you have big gaps or didn't have quite enough insulation.

Before you insulated and plastered the garage ceiling, was there any plasterboard fixed to it, or were the garage ceiling joists open?
I think he should check for drafts around the skirting etc.
As a comparison ,

the 100mm of quilt you put in is half what meets the minimum building regs requirement of today.

As others have mentioned I would check for draughts , if you do add another skin of plasterboard i would seal the perimeter edges first , and of course tape the joints .
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agree with Robert.

our latest extension required 10" joists above the garage simply to acommodate the required thickness of insulation!

the rest of the build had 7" x 2" joists.
Thanks for the replies. Would like to add that I already have over 270mm roll insulation the attic as well as cavity wall insulation. The joists above garage could only accommodate 100mm insulation and they now have a plasterboard and plaster covering as the garage ceiling. There are no noticeable draughts in the rooms above. Is it ok to attach kingspan boards to this plastered ceiling or would it be better to fit a suspended ceiling in order to accommodate more insulation roll? Thanks!
If you had fitted another 10mm to the roof insulation to make 280 mm, you would have achieved the presently required U value ;)

I would be tempted to provide a suspended ceiling , with the void packed with quilt .

This will also help reduce any noise nuisance that you may suffer from the street , through the garage door
I've got the same problem with my garage extension!

The room above has some loft space but also sloping sides as it is parltly built into the roof above.

It was built fully insulated with the marvelous multilayered foil insulation ( equiv to loads of rockwoll insulation) - but it doesn't work!!!

I've had cavity wall insulation put in, beefed up the loft insulation, now I'm going for the same approach as you.

I've got to take down part of the plastered garage ceiling, to check thickness of the insulation installed and beef up with celotex ( sealing air gaps as I go).

From reading arround, I think the cold bridging across the floor joists could be adding quite a bit to the heat loss, as it is feeeezing in the garage! So I am also tempted to use an insultated plasterboard, either as a replacement for the existing, or on top of the existing.

Let me know if yours sticks!

The sloping roof sides are a bit more of a challange! I haven't thought how to do them yet ( poor axcess and not very deep).
Watching Holmes on Holmes on telly the other day. (Canadian builder who goes round fixing cowboy jobs) and this very problem cropped up. His solution was to use sprayed in foam, the very stuff we turn our noses up at in the roofing forum. I'm partially convinced. Good insulation values and no gaps, dunno what it costs though.
the one problem with anything sprayed on Deluks, is it is so final.

like rendering or painting brickwork. at least a push fit insulation can be removed and put back.

imagine if you had to run a cable through after. :eek:

it will never convince me.
I would never buy a house that has had that stuff anywhere near it.

Proceed at yur peril

The work of the devil imho
i am a nurseryman and we use an underheated mist unit.

anyone who tells you that heat rises is not entirely correct

at least 15 to 20% is lost downwards in contact with the ground

this may even increase into a cold air space

so you are right to insulate that garage roof space i think that sprayfoam is best for you if the price is right cus it will be ventilated from above and below so no danger of sweating

we use expanded polystyrene sheets under our mist bed (with sand on top)
It's not so permanent, the stuff does stick like you know what, but it's easy to cut out once it's gone off. Common sense would put some conduit in before spraying anything anywhere, and if not you could easily cut a channel through with a sharp knife. I agree not so good for roofspaces but in a ground floor ceiling can't do any harm.
I think it's worth dowin it ... as most Building Control guidelines are essentially looking for a total "cell" of insulation ... thus the obession with floors and walls , as well as ceiling voids.

If you get Building Control involved ... be aware there will be proper demand for fire protection between the garage and anything else.

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