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chezseans 12-15-2009 10:15 AM

garage ceiling moisture
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when it gets cold outside the ceiling at the front of our garage (near the doors) gets very wet, sometimes even "raining" a bit as it drips off.

I will attach a diagram of what it looks like, but the floor of the room above the garage is spray foamed from below. There is then an open space that is essentially attic. The drywall ceiling in the grarage is not insulated and there is no vapor barrier. I did an inspection last year and it's bone dry up there. Only getting wet on the inside of the garage.

I thought of getting the ceiling spray foamed since there is no vapor barrier, but I don't think the framing is strong enough to hold someone all the way to the back to get it installed. Is there any other way to insulate without using a vapor barrier or do we have to take the ceiling down and redo it with the barrier/insulation in place ? or can I insulate the roof to make this space a little warmer?

the garage is not heated but we do have insulated doors and it does warm up once we park both our vehicles in there after work.

Thurman 12-15-2009 11:25 AM

From your description, and the drawing you posted, I would say that your problem is just plain old humidity building up on the ceiling of the garage. No matter what the temp is in the garage, you will have the "warmer" air rise to the ceiling, carrying the moisture with it. Then the colder attic space above the garage will cause the moisture to condense, form droplets and "rain" down as you describe. What do you currently have as far as ventilation for your garage, if any? Depending on your location you may have to install/place a fan to exhaust air from your garage. Do you know anyone who has a de-humidifier you can borrow for a few days? Place this in the garage to see just how much moisture/water is actually within the air in your garage. Good Luck, David

chezseans 12-15-2009 11:37 AM

Thanks. I am in southern Ontario Canada. I thought if I insulated that ceiling it wouldn't be as cold on the garage side so there wouldn't be anymore (or substantially less) condensation.
I do have a dehumidifier but I thought it wasn't a good idea to use them in an area that was below freezing. It's not quite that cold yet but will be soon enough.
There is no ventilation other than some spots where the garage doors are not as snug as they could be. I am not sure we are allowed to put vent fans in the garage as everything has to be sealed for exhaust/fire regulations

mattrleger 02-08-2010 01:49 PM

Garage Moisture
These are all classic symptoms of inadequate ventilation, with high R-value these days, the humid vapors have no where to go and left untreated cause problems. All you need is to supplement your garage with a little ventilation to remove that problematic air mass and exchange the air, and protect your investement from moisture related issues, like condensation, mold, corrosion. I purchased a garage unit called Wizzvent and it works great, 60 CFM and only uses 19 watts for around $200. Check out their website at

Hope this helps.

Thurman 02-08-2010 02:35 PM

Yep! Basically a de-humidifier to control relative humidity, and with an outlet leading to outside to vent the excess humidity. Good call, nice idea. David

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