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Garage roof - insulate, or not?


AntonyH

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Kind of technical...

 

Detached unheated garage, single skin brick walls (waterproofed), single skin steel sheet roof on wooden joists, concrete slab floor.

 

Air brick high up near back of garage, plus the roller door does not hermetically seal at the bottom and definitely not at the top.

 

Dry inside plus a dehumidifier to take care of the excess if e.g. it's raining when we get home and the 7 goes away damp.

 

Considering insulating the roof with a ply inner skin and some fluffy stuff in the gap, just to keep the temperature a little more stable; opinions on whether this will be of any benefit (beyond being a fraction warmer if working out there in the winter!)?

 

TIA

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I don't think it'll make a difference at all. If you are getting condensation dripping off the roof you could always line the underside of the joists with visqueen (polythene sheet) or buy a breathable car cover. Might also be an idea to put some visqueen on the concrete floor under the car possibly with some carpet on top.

 

Dave *smile*

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Hi

Condensation is all about the dew point witch basically is a calculation between the outside temperature the inside temperature and the humidity in the air. Insulating the roof will stop the condensation on roof panels as this will keep them nearer the temperature so the outside of the panel so should help if there are no other issues with the walls and floor that may cause high humidity .

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  • Leadership Team

Insulate *thumbup* Your garage is the same construction as mine except for the steel roof, mine is felt and tiles therefore will not suffer from condensation as badly. Is the roof at a high pitch or is it fairly low? My choice would be to insulate with a separate barrier below the steel sheet with the air brick then in the created cavity ... effectively similar to an insulated loft. Adding insulation directly to the steel sheet may cause a bigger damp problem, modern insulated roofing sheet has the layers bonded together preventing moisture ingress, you're not going to be able to reproduce that.

Maybe consider a suspended ceiling as the method of insulation? Reducing damp is the key to keeping warm, only then can you add more heat if you need it.

 

Stu.

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Thanks all for the suggestions / input.

 

Stu, sadly the roof is very nearly flat (very gentle incline to the rear) and the bottoms of the beams are not much over head height, plus the air brick is about my head height, so a suspended ceiling with a void to encompass the air brick isn't feasible unless I want to stoop!

 

Best I can manage is a lower skin at the level of the bottom of the beams.

 

 

Siva, if your garage isn't below the surrounding ground level then this water seal from Wickes might help - made a huge difference to the water ingress in ours. You need to make sure the pointing's all good first (no big gaps and cracks) then just brush it on to the brickwork. It soaks in then sets to form a waterproof barrier (apparently). Changed our walls from being a masonry sponge into something that actually holds out almost all water. Just a couple of tiny leaks now, one where I hadn't done the pointing in a gap (D'oH!) and one where we maybe just missed a bit.

 

PS. When it says "use in a well ventilated area" it really isn't kidding.

 

 

*smile*

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