tegwin
|
| posted on 12/2/13 at 10:44 PM |
|
|
insulating garage roof...condensation issues
Right then...
Garage is a single concrete block construction. I built a new roof on it last year but stupidly (couldnt afford to) didn't insulate it.
Regret this because it gets rather cold inside as the roof is just OSB and a thin layer of plastic...
My lathe and other tools are slowly starting to go rusty so I figured if I could insulate the roof to prevent heatloss I might be able to run a small
heater to dry things out...
My plan was to fill the "cells" between the rafters with 6" of insulation foam leaving a gap between the foam and the OSB roof deck
so that air can flow in under the weatherboards and between the insulation and the underside of the roof deck..
All good so I order some insulation and put up half of it... went back the next evening to find condensation dripping out between the rafters and the
insulation... The sun had been out so I guess it had heated the area above the insulation and then when the temp dropped it all condensed...
My question is, what do I do!? Carry on fitting the insulation and try and seal the joints with tape!? All I want is the garage to be a little
warmer/dryer...
Any thoughts!?
Half the insulation up:
Empty "cell"
Condensation 
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
|
|
|
|
|
coyoteboy
|
| posted on 13/2/13 at 12:05 AM |
|
|
Condensation occurs where warm moist air hits cold surfaces. If the bulk of the garage is poorly insulated you won't stop the roof being cold
inside and poor ventilation means you'll get condensation on any cold spot. I have similar issues, but I'm resigned to re-building the
garage with insulated walls and fully sealed structure rather than the sectional arrangement that I have now (trust me, I can't get any more
ventilation!). Often I find my donor engine running with condensation.
That's a very large turbocharger at the back there.
[Edited on 13/2/13 by coyoteboy]
|
|
|
cliftyhanger
|
| posted on 13/2/13 at 07:56 AM |
|
|
Where is all the water coming from? I suspect no membrane in the floor. You need to get rid of the water, heat won't do that (the air just holds
more water, so when it cools it creates more condensation)
My non-insulated garage isn't anywhere near as bad as yours sounds, but I do have very good ventilation. Either that or seal everything and get
a dehumidifier in there.
Now, 6" of board is massive (you must have deep pockets!!) and an inch would /should be enough for what you are trying to achieve. I think it
needed to be hard up against the roofdeck, as there is no way you are getting airflow between at the moment.
On another note, I hope you used treated timber, not clear from the pics.....
You could be fighting a losing battle here. The old saying involves silk purse and sows ear I believe. Not helpful, but you may need to be realistic
about what can be done with what you have. And if you need to start from scratch
|
|
|
jossey
|
| posted on 13/2/13 at 08:45 AM |
|
|
Insulate the walls with that silver foil cheap stuff. Won't solve the issue but will make it better.
There is no answer in a garage really.
I use a dehumidifier when I'm working in the garage.
Dry air is a lot easier n cheaper to heat too.
Good luck....
Thanks
David Johnson
Building my tiger avon slowly but surely.
|
|
|
Peteff
|
| posted on 13/2/13 at 09:05 AM |
|
|
Take the insulation out, glue the roof and stick it straight to it, you don't need airflow there inside the garage. Put some corrugated sheet on
the outside to add another layer of protection.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
|
|
|
tegwin
|
| posted on 13/2/13 at 09:13 AM |
|
|
Thanks for the input guys. Not what I wanted to hear but useful advice 
If I can get a cheap dehumidifier in there to dry the place out and then glue the insulation to the underside of the roof deck...that might be the
best approach... Any suggestions for a glue? I could use expanding spray foam but that stuff is pretty uncontrollable!
If I am running a dehumid unit in the garage am I going to have any negative issues? I guess the dry walls inside will encourage water from the
outside to "flow" through the walls... but the walls are rendered and painted so should be reasonably impervious...
@coyoteboy...Yes it is a BIG turbo :p Actually the start of a smal jet engine project...although I haven't touched it for nearly a year
[Edited on 13/2/13 by tegwin]
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
|
|
|
JeffHs
|
| posted on 13/2/13 at 10:31 AM |
|
|
I cured my condensation with 1 inch polystyrene jammed up to the corrugated roof sheets and held in place by 4mm ply. There's some water
staining on the ply but nothing ever drips. It's a crappy sectional garage because the council wouldn't let me have a brick one due to the
drains underneath it. Before I fitted the insulation it used to 'rain' inside when there was a sudden temperature change.
I've got an attached workshop that is roofed with clear corrugated sheet. That had similar condensation problems that I fixed with bubble wrap.
|
|
|
cliftyhanger
|
| posted on 13/2/13 at 11:09 AM |
|
|
4" nails in the joists keep the boards up no need for glue.
Try the silicone water repellent on the outside of the blocks. Maybe inject the floor slab?
even batten/board the inside of the walls. Thin polystyrene behind can help a lot too.
Dehumidifiers can be shockingly expensive to run constantly, and you MUST get the place sealed totally otherwise you are dehumidifying fresh air all
the time.
|
|
|
Not Anumber
|
| posted on 13/2/13 at 11:10 AM |
|
|
+1 for bonding the insulation directly to the roof. The void between the roof and insulated cieling is working against you here. The cold air gets
into the void, condenses on the roof and water drops down on the top of the insulation.
Use gun grade expanding foam to bond the insulation to the ceiling and to seal the edges to the rafters. This is similar to the DIY stuff that places
like B&Q sell but the gun makes it an awful lot more controlable, chalk and cheese. Its what all the wndow fitters use. Places such as Screwfix
often do a deals on a foam gun budled with a couple of cans of foam and a can of cleaner.
If you can sarfifice a tiny bit of width in there then glue sheets of closed cell insulation to all the walls. 25 to 30mm will make a big difference,
50mm ideal if you have the space. So long as there isn't dampness getting in thrugh the floor or leaking in somewhere your condensation
problem will have gone away and you will have a garage that will be very easy to heat and will stay warm.
|
|
|
BenB
|
| posted on 13/2/13 at 11:59 AM |
|
|
Yup. Heat rises so the hot water vapour is going up into the void, condesning on the underside of the roof and dripping down. Personally I'd
just leave the insulation in place and seal around the edges with some silicon sealant (you could use expanding foam but doing that overhead sounds
unfun and its godawful messy stuff).
|
|
|
JoelP
|
| posted on 13/2/13 at 07:55 PM |
|
|
As has been alluded to, the problem is when warm wet air gets behind the insulation. You would only want ventilation above the insulation if it is
venting to outside, like your house eaves. Typically you would have a damp proof membrane on the warm side, specifically to stop air getting round
it. You would also normally have a breather membrane on the outside below your tiles (allows water vapour through but not drops), to ensure water
doesnt get trapped inside the roof structure - but this is more for houses than garages.
If you can insulate the walls to some degree, then a 100w light bulb can be a nice way to keep some steady heat in the place. Maybe a damp meter on
the floor to see if this is sweating damp through?
Beware! Bourettes is binfectious.
|
|
|
van cleef
|
| posted on 13/2/13 at 10:42 PM |
|
|
The only reason it is causing condensation is because your leaking warm air above your insulation. You need the insulation air tight around the edges
and silicone isn't really any use as it has no thermal value. Best thing is probably expansion foam and trimming the excess off after it has
fully cured. You should have a high u value with the thickness of the insulation there, and having a gap above the insulation shouldn't cause
any harm, as long as the air above it is roughly the same ambient temperature as outside, hence not leaking any warm air into the cavity above.
If that's a flat roof on the outside you should of created a warm roof from the outside doing away with any cold bridges if you wanted to heat
the garage.
http://www.flatroofs.co.uk/flat-roof-insulation/
|
|
|
