Insulation, Radiant and Vapor Barriers - Insulating Garage

Hello,

My garage is approx. 200 square feet and is connected to an unheated mudroom. We use the mudroom as a pass-through to the kitchen. I recently blew-in celluose insulation into the mudroom walls that were already insulated with traditional fiberglass insulation. Now I am considering insulating my 200 square foot garage that is unheated. One wall (warm wall facing living space) is already insulated and sheetrocked. The other two walls are open with studs 16 o.c. as are the roof beams and rafters. I want to insulate the wall with Owens Crng fiberglass insulation and close it off with either sheetrock or t 1-11 plywood. I also want to insulate the roof as well but I won't be closing off the roof as I'm planning a drop ceiling. My question is considering I do not have a ridge vent OR soffit venting (no soffits) will this approach be problematic in terms of moisture and lack of ventilation? Thanks

FC

Hi FC, snow and rain from a vehicle must go somewhere. Without heat, it will condense on the walls and ceiling or seep through the insulation or drop ceiling and condense on the roof deck and rafters above. If you NEVER introduce moisture, in other words don't use it as a garage or living space, then less of a problem. Your home is in balance with the moisture generated being vented enough to keep the relative humidity (RH) level below 50%. A cold garage starts at a very high humidity potential because it is cold. RH goes up as the temp goes down and eventually condensation forms.

As for the attic venting, you should have some. There are roof vents, gable vents, edge vents, and even the ridge vents can be added.

What will be the use for this garage?

Bud

Thanks for your response Bud. For the most part the garge will be used for storage and as a pass-thru to the main residence. The only time we will park our car in there is if we have a bad snow storm. Other than that the cars won't be in there. Might use it for tinkering around a bit.

The time you want to be careful is when the car is covered/caked with snow and it would be nice to melt it off. Some jerks decided to do that in a huge garage I was building and we just had kraft faced insulation up. It worked great for them over the weekend, but when I returned Monday I spotted the water marks in the bay. They fessed up and said no problem. I took them over to one of the exterior walls and removed a length of insulation. 1/4" of frost the full length. Had to R&R all of the insulation to dry it out. That was three cars loaded with snow.

So the water goes somewhere.

Enjoy,
Bud

Thanks again Bud. I plan on going with the r-19 owens corning. should i use the faced or unfaced for the garage walls and roof? Thanks

FC

Faced in the walls is easier, but I like a 4 mil plastic covering in addition. 6" unfaced actually goes up and stays in place very well. In the ceiling, faced if you are installing before the drywall, otherwise unfaced from above. Again, use a good VB.

Bud