We've got a fairly standard 1970s/80s detached garage (brick and block walls and tiled pitched roof), I want to insulate it to keep it a little warmer in the winter and am considering replacing the door and installing some roof insulation, but I'm getting really confused about how to insulate the roof. I've tried searching google, but just find arguments about vapor barriers and overly complicated/expensive arrangements which involve taped joints and ventilation tiles etc! Is there a cheap and simple solution (that will work and won't cause the roof to collapse) or will it end up too expensive / more effort than it's worth when I could just put on another jumper?!
Can you see the trusses and the sarking felt?
Just buy some slabs of Kingspan and cut them to the right width then press them in between the trusses.
Yes, looks a little like this (google image and not actual garage roof!):
Do I need to worry about air gaps etc if I just wedge slabs of Kingspan between the trusses?
If you just push insulation in then you will end up with a cold deck roof and that needs proper ventilation or the wood will rot. You will also probably end up with lots of air gaps largely negating the benefits of insulation. I'd maybe go for a space blanket style insulation stapled to the timber with an air gap and ventilation. Just stopping the draughts will make quite a difference. It'll still be cold in winter though
A couple of choices:
Create a suspended ceiling that you insulate (big space between it and the existing roof)
or
Have a look at your soffits and if they are ventilated (i.e. have some sort of grill in them) then you'll need to maintain the ventilation. You go this by putting insulation between the rafters but leaving a minimum of 50mm gap between the top of the insulation and the felt.
If you have a breathable membrane rather than felt (doubtful on an 80's build) then you can push the insulation up to it and not bother with the 50mm gap.
Just be warned that kingspan type stuff is pretty expensive and, although it's easy to cut, it's a royal PITA fitting it as it's such a dusty job.
(you should also [expanding] foam the gaps that you will inevitably leave)
Will anything really make a difference unless you heat it as well?
Insulation will make it cool down slower, but over winter it's got all the time in the world to cool down so it will still be cold.
It might be slightly warmer for a bit in the evening on days when it's sunny during the day but cold overnight, but other than that I don't think you'll see any difference...
Will anything really make a difference unless you heat it as well?
To some extent. It will be just as cold without any heating but it should hold the heat better. My workshop is well insulated, its freezing in there in winter but a small heater takes the edge off very quickly and just being in there with a few tools running is enough to keep it warm-ish. Insulating will also reduce the draughts which will make quite a difference even without heating.
Will anything really make a difference unless you heat it as well?
I've got a small heater which I don't use much as heat just distastes out the roof and gap around the door! I also want to put the washing machine in there (once I've sorted the plumbing) so need to make sure the water supply doesn't freeze!
