Moisture issues

[Nordic Home Inspection]

Came over an interesting issue in a garage the other day:

This picture shows ice on the overhead garage door. To the left you can see there is ice on the sheet rock as well.

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There is ice on the garage ceiling. Looks like water drops.

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This one is from the attic above the garage, and there is ice under the vapor barrier.

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[Tom Raymond]

There is a ton of warm moist air leaking into that garage from somewhere. I'd check the fire door to make sure the spring hinge is working, I'd bet not 'cause they like to leave it open.

How cold was Fargo today?

[Garet]

Hmmm. There's definitely a moisture source. Ordinarily, air leaking from the living space would be my first assumption as well. But there's another possibility. Just thinking out loud here.

I assume there would be snow tracked into a garage in Fargo (insert big smiley face here). Could a warm vehicle engine be evaporating the moisture into the air, only to have it condense when it hits the cold surfaces? If occupants were making many short trips each day (re-warming the engine) that could add to the effect. The air in my garage is always damp when we track snow in. We don't get as cold as you and not for as long, so I haven't see frosting like that.

[Chad Fabry]

Exhaust is mostly water- running a car in a closed garage would be like running a big humidifier. Is there someone dumb enough to warm up their car in closed garage? Never mind, I'm remembering the local headline from a few weeks ago, "Couple Killed by Carbon Monoxide" they were running their generator in their basement.

[Terence McCann]

Is the attic in the garage also attached to the homes attic? If so any humidifier(s) in the home?

[John Kogel]

Yes, that is also possible. Anywhere there is a drastic temp differential, there will be condensation.

The warm air could be from a heater or an open door.

I doubt that they'd leave the car engine running in there for very long, but they might plug in a block heater and along with melting snow, cause some moisture to rise.

Is it normal to have uninsulated attached garages in Fargo?

[hausdok]

It's easy to explain,

You drive the car into the garage and the snow, or the Seattle sunshine, falls onto the floor, evaporates and then condenses on the nearest cold surface. Around here, the condensation ruins wood overhead doors that haven't been primed or painted on all sides and edges as specified by manufacturers. When it's cold enough out, which is not very often, it freezes on the inside of the overhead doors just like it's doing there.

We don't use vapor barriers here; but, occasionally some horse's ass with teeth will incorporate one into a building envelope because he hasn't done his research. In any garage where there isn't any sort of vapor barrier on the other side of the drywall, the vapor harmlessly diffuses into the attic where attic ventilation removes it. In an attic with a vapor barrier against the back of the drywall, that same vapor will go only as far as it can before it hits that plastic and the freezing cold temperature on the other side of the plastic causes the vapor to freeze. Over time, it builds up. I'm betting you have a nice tightly gasketed garage door to prevent snow blowing through and drifting into the garage, no?

I agree with what others have said; if they are warming up the vehicle in the garage, even with the door open, a lot of water vapor ends up in the garage. When I was a teenager, it was my job on cold mornings in upstate New York to go out in the garage and breezeway and start up each of my parents' cars and turn on the heaters. Our "garage" was more of a carport; it was a garage in every sense of the word but Dad never installed an overhead door or a door between the garage and the breezeway, preferring instead to leave it open. It made for an interesting time getting in and out of cars after an overnight storm would dump a couple of feet of snow on the ground. When I'd warm up those cars, the steam from the exhaust would fill the garage and breezeway and condense all over everything nearby, walls, ceiling, workbench, tools, etc.

I wonder if they put the vapor barrier in the walls and ceiling of the garage but left it out of the wall between the house and the unheated garage?

The vapor barrier is only needed around the inhabited portion of the building envelope and should not have been installed in the garage. Imagine if you kept one room in the house in your climate that was never heated; vapor diffusion would push moisture-laden interior air from the warmer parts of the house into that unheated room, and then, as that moisture migrated into the cold exterior wall of that room, it would condense and start causing massive mold to grow behind the drywall. All that simply because you failed to keep that room at a reasonable temperature.

ONE TEAM - ONE FIGHT!!!

Mike