Insulating the garage ceiling: worth it?

[Another John]

As the nippy evenings and cold nights become more frequent again, I'm once again thinking about insulating the garage ceiling.

- The garage is roughly 6m by 4m, and our bedroom is above it.

- The bedrooom often feels rather cooler than the main house (admittedly it's a big room, therefore "airy").

- Yes. I know that bedrooms are supposed to be cooler than the rest of the house, but I'd rather achieve that by turning down the radiators.

- I keep thinking about sticking (say) 50mm Celotex boards to the ceiling [of the garage], using mastic of some kind.

- Would it be _worth_ adding more insulation? When built, 25 years ago, as an extension to our semi, the joists above the garage were packed with insulation before the plasterboard was fixed. We also have a roller door fitted, therefore pretty good insulation at that end.

- The whole house is very well insulated in the roof, and also with cavity wall insulation.

Any comments would be welcome, to help me with this decision!

Cheers John

[harry]

If you have an integral garage there will be fire resisting material on the ceiling to prevent any fire in the garage spreading to the house. It might be fibre cement board or extra thick plaster board. The last thing you want is flammable insulation.

would be non-flammable mineral wool between the joists.

[polygonum_on_google]

I certainly wouldn't stick insulation up with anything.

I think my first action would be to check the bedroom with an infrared thermometer and, with great care, a candle. Looking for cold spots and draughts.

If, after investigation, you still consider it appropriate to add insulation to the garage ceiling, don't leave it bare. Cover it with plsterboard (or whatever is approved) and fix with the sufficient screws.

[Andrew]

Pull the garage ceiling down and make sure there are no gaps where the joists are built into the walls. Seal with firestop mastic if so, then in place of the fibreglass or whatever they used 25 years ago, cut 4 inch thick celotex so that it fits *tightly* up against the bedroom floor and use tile battens to provide extra support. infill remaining space with whatever fibreglass you pulled out then add another layer of celotex over the joists (ie.on the underside), and fit new 15mm fireline plasterboard.

[Andrew]

Something else just occurred to me. Does this extension have the same roof line as the original house or did the planners insist on a 'set back' ?. That being the case are the bedroom windows dormer-type windows ?. This style of construction is notoriously leaky where heat is concerned. 25 years ago the builder probably didn't put any insulation in the dormer cheeks, and quite possibly little of none above the ceiling. Retrofitting this is not going to be easy.

[Bill Wright]

I have a garage, utility room, and storeroom below the main house. The garage door and adjacent pedestrian door are north-facing and because we are on high ground with a slope coming up to the house from the north there's almost always air coming in. The kitchen was always very cold indeed in winter and it turned out this was due to countless small draughts coming through the floor in-between the boards and round the edges. I put a plywood floor down in the kitchen and sealed all round the edges. I also sealed the garage ceiling (there were holes for cables and pipes). These two measures made a massive difference.

I find it helps to keep the door between the garage and the hall, and the one between the hall and the utility room, closed in winter. This reduces draughts coming up into the office above the storeroom, which is off the utility room. I have put a plywood floor down in the office but it hasn't been completely successful for some reason.

Bill

[John Rumm]

If the garage is used as such then you should have a 30 min fire break below the new insulation.

You may get a bit of cold bridging on the joists... how much difference it will make is a harder call. However if the garage is relatively clear, then its a easy enough job once you have worked out where the joists are - you can screw through the new PB and the insulation in one go into the joists to fix it.

I helped a friend do a garage conversion some years back. One of the comments was after the work that the bedroom above was now much warmer as a result of now having a heated space below.

[Brian Gaff]

Well one assumes that the fact it has three outside walls might be a factor, even if insulated. I guess I'm thinking that somehow you need to decide if the cold is actually coming from the unheated garage and not for some other reason.

Brian