Attic Moisture In Attached Garage

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Old 01-02-08, 04:05 PM
Don W's Avatar
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Attic Moisture In Attached Garage

We have a 3 yr. old ranch house with an attached garage. Last night got very cold and when I went out into the garage today, I noticed heavy frost on the front panel of the breaker box. There was frost on the door knob of the service door as well as frost on the dead-bolt. The service door had frost on the molding from about knee down. These are all on the same outside wall. Inside the garage the snow on the cars had melted from the night before and had pooled under the vehicles. When I looked up on that outside wall where the ceiling meets the top of it, at every joist location there was a wet spot. The walls are insulated with faced R-13, sheet-rocked, taped & mudded, no paint. The ceiling has blown-in fiberglass which the builder said equaled R-30, no vapor barrier, sheet-rocked, taped & mudded, no paint. Service door and garage door are insulated, no insulation behind breaker box, just around it. We have ridge vents, which the builder said was plenty when I asked for gable vents as well. The house and garage attic are not separated as with foam board or insulation. Why in our third winter in the house, do we suddenly have a ventilation problem? This wall is the furthest away from any living area. What's going on?
 
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Old 01-02-08, 05:48 PM
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Is the garage heated? If not, how did the snow melt off of the cars. The condensation is caused by temperature change. If the temperature went from warm to cold, the water vapor in the warm air would condense on the first surface to reach the dew point. Metal is a better conductor so it would reach the dew point first. Next would be the least well insulated areas. Thermal bridging by the framing members would be the next to cool. I'm not sure you have a problem, just a set of circumstances that caused a lot of condensation.

It would probably be advantageous to get some primer on the bare drywall before moisture rises to the point where mold or mildew begins to form on the paper.


Ken
 
  #3  
Old 01-02-08, 06:59 PM
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The garage isn't heated. My wife and I are in the habit that when we come home the garage door goes down right away. The heat from the engine melts the snow and the garage stays warm enough not to freeze the puddled water. I was wondering whether to change my habit and leave the door up long enough for the engine to cool down.? The temperature swing went from 30 to about 4 degrees, so it was already under freezing. I'm thinking that I should do as you say with the primer, and maybe squegee out the pooled water. The area in question in the garage attic is framed by the trusses so the end result is a cubby hole. I can't get close to inspect it or to feel if the insulation is wet due to the roof slope and the confined space. (Damn that tastey beer!) What do you think of the idea of isolating the garage attic from the rest of the house with foam board?
 
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