Inside garage walls and roof sheathing frosting in cold weather


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Old 02-20-24, 02:42 PM
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Inside garage walls and roof sheathing frosting in cold weather

Built a new garage in late fall, roof is on but siding and soffits still needs to be completed. Every time we have a very cold night I have frost on the inside of my wall and roof sheathing, my roof sheathing is beginning to get mold on it. In between my truss joist I have no vent baffles yet, I just blocked my baffle opening with insulation to keep the cold wind from blowing in during the winter. Could this be the reason I'm getting frost build up inside, not enough air circulation?


 
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Old 02-20-24, 02:49 PM
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You get frost on your car windshield too.

It's a weather phenomenon. Anything below the dew point temperature will get condensation. If it's below 32F, that condensation will be frost.

The relative humidity often is highest by the roof since warm moist air rises and a roof in the shade or with snow on it is cold.
 
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Old 02-20-24, 03:58 PM
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You've blocked off the ventilation and now have a condensation problem.

My hangar, a uninsulated steel building, would actually rain inside under certain weather conditions. Warm humid air trapped inside from the day then the temperature plummets at night. Moisure condenses on the cold surfaces into liquid water.

You have an uninsulated room/building so I would give up on the idea of keeping the heat inside. It (the heat) will be gone soon enough. You need to get the inside weather to match the outside as closely as possible. So open up those soffit vents and hopefully you've got a ridge vent or soffit vents to generate some air circulation.
 
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Old 02-20-24, 05:02 PM
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I do have a ridge vent, I'll remove the insulation and put in soffit baffles between the joist to get the air circulating and help remove the warm moisture trapped inside the garage all day. I guess I created my own problem, it all makes sense to me now what's going on, thanks for the help..
 
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Old 02-21-24, 07:14 AM
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I would consider installing a simple ceiling to the underside of the wall ties. Then opening up the soffit and allowing free air circulation in the “attic” area. Years ago I had a similar issue. The heat rising off warm cars caused ice dams on the topside of the roof as well. I stapled sheets of that aluminum covered bubble wrap to the wall ties/ceiling joists. That kept the heat and humidity within the garage area and isolated the roof. I was pleasantly surprised by how warm the unheated garage stayed with only this foil stuff as a ceiling. Never bothered to finish the walls on the inside, never added any insulation to the walls either. This was a detached garage at 8500 foot elevation.
 
 

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