Hi,
Im in the process of insulating the roof of my garage.
I am planning on using 50mm Celotex between the rafters. Due to cost, I was planning on using 25mm polysterene from B&Q over.
Would I still need the vapour barrier plasterboard ? Or if I ditch the polysterene could I just tape up the joints where the Celotex meets the rafters and use standard plasterboard ?
Thanks,
Matt
Take sheet of non-vapour barrier plasterboard. Dilute PVA to milk-like consistency. Arrange some way to prop up the sheet so that it's off the floor, vertical, or sloping slghtly backwards, with the long side parallel to the floor. Spray a meter with the PVA solution from a small pump-up sprayer. Lay two lines of kitchen foil, slightly overlapping. Spray another meter, repeat.
This gets you a foil coated bit of plasterboard for well under 30p, and in under 5 min or so.
No. But its so little extar cost, why not?
Or if I ditch the
Yes..but see above.
Whereas the extra cost of the foil backed plasterboard is probably about
10p for the same area..
If you can find it in stock .... Wickes don't sell it, not mine anyway
why plasterboard a garage roof/ceiling? Plasterboard won't perform well in an unheated building. Where foil backed PB is specified in construction it's to prevent warm moist air from an inhabited space condensing out in a cold space. You seem to be expecting the vapour barrier to prevent moisture vapour entering your garage. Not necessary due to ventilation of the garage space and would be a bad thing for your roof structure.
Jim A
Oh well. I got quoted an extra fiver per sheet. Kitchen foil is only 10p/sheet or so.
On 29 Nov 2006 04:07:48 -0800, a particular chimpanzee named matt snipped-for-privacy@yahoo.com randomly hit the keyboard and produced:
Why are you insulating the garage roof? Is it for frost protection (with some low-level heating) or are you going to heat it significantly? If the former, then you probably won't generate enough condensation to worry about. If the latter, then you're going to need more insulation anyway.
You'll get better value from your insulation if you use the Celotex over the rafters and the polystyrene between. There is heat lost through the rafters and the more insulation you can cover them with the better.
To put some numbers on this - wood has a conductivity of about three times that of rockwool or polystyrene, and six times that of kingspan.
Mine does, and since it's only a few hundred yards away, that's where I buy it. I think they might have foil-backed only in 9mm though.
Technically, the top layer of insulation has to be better or the same than the bottom layer of insulation. That means that if you have 50mm Celotex between the rafters, you can have either have up to 50mm below the rafters, or 50mm or more above the rafters. The top layer being polystyrene makes it even worse.
This is to avoid condensation forming between the insulation layers.
If you are going to suck it and see, then DEFINITELY use vapour check plasterboard, as that will significantly reduce the problem. Taping the celotex with foil tape would, I presume, have a similar function to vapour check p/b.
Christian.
enough for mow much? and then add in glue, your time...?
I didn't think plasterboard was much more than a fiver a sheet last time I looked anyway..
I got quoted 10 quid a sheet for vapour barrier, 5 for not.
Tesco do foil for 68p for 3m^2. It used about a litre of PVA for 24 sheets.
It takes about 3 minutes per sheet to do (once I stopped being silly and getting a perfect mirror finish on each sheet of plasterboard, with no wrinkles and perfect butting joins, which was admittedly very pretty, but diddn't add a whole lot).
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