prawnabie
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| posted on 5/12/13 at 08:18 PM |
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Stopping condensation/insulating a garage roof..
Hi everyone!
I posted a while back about getting my parents garage ready for the winter. I have been clearing it out and have some more questions...
It is a concrete sectional garage with an asbestos corrugated roof. It seems the roof has numerous leaks around the sides and is porous in places and
has been bodged with bitumen paint over the years. There are 12 sheets of 50mm thick 8x4 polystyrene in the garage I can use so I have the following
plan..
Cover the exterior of the roof with polystyrene sheets, creating a flat roof (there is a slight incline on the roof for drainage and the side of the
garage are approx 12" higher than the roof). I have enough EPDM pond liner to cover the roof twice, so 2 layers of this will go over the roof -
that should make it waterproof.
The roof is held up by 5 concrete joists with roughly a 1.2 meter gap between them (the end 2 being part of the end walls). I was planning on wedging
more poly sheets between the joists leaving a 10 -12mm gap between the poly and the roof and sealing the gaps up with expanding foam to stop any warm
air getting into the void.
The only problem I can see is the end joist above the main garage door also acts as gutter (rainwater comes off the roof onto a trough cast into the
joist and runs into a built in down pipe in the side pillar). The gutter is basically inside the garage and will be in the "void" that the
insulation will create. Although this will create an air gap for circulation, I am worried that water will cause moist air in the void and defeat the
point of me trying to stop condensation.
Can anybody see any problems with what I am proposing to do?
Thanks in advance
Shaun
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MikeR
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| posted on 5/12/13 at 08:41 PM |
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yes! you may still have problems if you bodge it.
read up on warm roofs and cold roofs. two different approaches to roofing. I think your doing a warm roof. follow that guidence and you'll be
fine.
how are you going to secure the pond liner so water doesn't seep through the nail / screw holes?
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cryoman1965
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| posted on 5/12/13 at 08:48 PM |
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Will the pond liner deteriorate in direct sunlight?
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prawnabie
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| posted on 5/12/13 at 10:08 PM |
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Thanks for the replies!
The garage will be knocked down as soon as I have built my kit, so this is only meant as a short term fix - I don't really want to spend a
great deal of money on it.
The sides/front/back of the garage extend above the roof by about a foot, I am going to no nails a batten around the garage to secure the pond liner
to - thanks for the info though Mike I will look into that.
The Pond liner is UV resistant so it should last as long as I need to be in the garage - I have plenty more so replacing it shouldn't be a
problem in the future if it doesn't last.
The main priority is getting the roof waterproof - I am hoping to do this on saturday. I can then concentrate on painting the floor/insulating the
rest of the garage.
Thanks
Shaun
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dhutch
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| posted on 6/12/13 at 09:06 AM |
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While I would be slightly carefully how much weight you put up there, you could proberbly do worse the weigh down the middle of the liner/cover with
something like tyres or 2*3 timber laid ontop as per silage clamps!
Asa single-season bodge using what you have it sounds plausable, but as always the devil will be in the detail of how you finish the edges etc which
without seeing it is very hard to visualise. The Polystyeine board will be open-cell so while it will befairly spash-proof as a one-off, if it gets
wet, as a drip runnign onto it, it will take on water and get very heavy and conductive!
Daniel
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steve m
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| posted on 6/12/13 at 09:32 AM |
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I believe you will only get condensation if you heat it with a gas or oil or any burning type of heater
Ive used fan or twin bar heaters in my garage for years, and have never had a problem with condensation
Also, I never allow it to get to hot out there, as that's just as bad as to cold, for working in so once the temp is ok, I will reduce the
heat
Ventilation is also a very good way of reducing condensation so possibly not filling EVERY hole or gap is the answer
Can I also add, that if your starting with an empty shell, paint it inside a bright colour cream or white, and you can NEVER have enough lights or
plug sockets
I have also covered the inside of the metal garage door with cheap polystyrene sheets, and then some alui bubble wrap foil designed for the back of
radiators, not sure if it helped insulate it that much, but wow it gets bright out there now with the reflection !!
Steve
Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at
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deezee
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| posted on 6/12/13 at 05:13 PM |
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To be honest I'd just get some spray roof foam and spray a nice 5" layer all over the inside. Seals the roof, insulates the roof and
saves seals the asbestos. Also it would take 30 mins, job done. your way is going to take days.
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prawnabie
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| posted on 6/12/13 at 07:12 PM |
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Spray foam costs money, the insulation boards and the pond liner are already in the garage.
Ive looked into what Mike has suggested and it looks like a "warm roof" is the way forward. The existing corrugated roof will form the
base with a layer of vapour barrier over it, then the insulation boards and a couple of layers of pond liner over that. This should hopefully move the
dew point above the old roof and make it waterproof at the same time.
Thanks
Shaun
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van cleef
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| posted on 7/12/13 at 09:28 AM |
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I'm a roofer who does EPDM flat roofs.
If your using it to build your kit then you'll need more than for than a short term fix as most kits take longer to build than you think.
Are you going to be heating the garage?if not you'll not need a warm roof system
If it was we I would ditch the corrugated sheets then create a new deck and work off of that. You'll really need to bond down the EPDM rather
than try and hold it down with timber with the winds we've had recently.
Or you could ditch the whole idea and use new anti condensation backed box profile sheets which can be picked up for around £10 per m2 or less and
sell what you were Originally going to work with.
Or paint the outside of the the roof with Acrypol fiberous paint which would get you through the winter which costs around £50 for 5 litres.
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