Insulation

[OverkillYJ]

I have a large detached garage I recently bought. A lot of the insulation was 30+ years old, black, and falling from the ceiling, so I ripped most of it out a month or two ago. I plan on insulating it again, but wasn't really in a rush to since my money has mostly been going into the house. Now that it is starting to get cool at night I am curious how high a priority I should make insulating it. I have a large amount of tools out there, some electronics, etc. I know it will be cold either way, I am more curious about the dew point in the garage. I was not sure if the insulation would prevent problems with moisture collecting in the garage overnight. Maybe it is no concern at all, but I don't know since I have never owned a building detached from the heated building where I would have to worry about it. I live in Philadelphia, so our winters are not horrible at all, but it does get cold at night, and now that the dew is on the grass and cars in the morning I wasn't sure if I should be concerned at all.

 

[sands35]

As far as dew point, the way that it is managed with fiberglass, cellulose or similar technology is to have a vapor barrier on the outside (housewrap for stick construction) and a vapor retarder on the inside (painted drywall and kraft faced insulation). There will be moisture at the dew point location, but it will dry out when it gets warmer.

Newer technologies (closed cell foams, SIPs) place the dew point in the middle of the foam mass, where (since it's closed cell) water can't get too. The problem with sprayed in solutions is managing the air quality of the building. Heat Recovery Ventilators are installed to exchange air with the outside and not loose heat/cold. The other issue with sprayed in solutions is managing the life of the shingles on the roof. for SIP roofs, a 'cold roof' is installed which allows air to circulate under the shingles and controls their temperatures during the hot season.

Some folks spray foam directly to the bottom of the roof sheeting. I'm pretty sure this would void the shingle warranty.

 

[fwillison]

As far as dew point, the way that it is managed with fiberglass, cellulose or similar technology is to have a vapor barrier on the outside (housewrap for stick construction) and a vapor retarder on the inside (painted drywall and kraft faced insulation). There will be moisture at the dew point location, but it will dry out when it gets warmer.

Newer technologies (closed cell foams, SIPs) place the dew point in the middle of the foam mass, where (since it's closed cell) water can't get too. The problem with sprayed in solutions is managing the air quality of the building. Heat Recovery Ventilators are installed to exchange air with the outside and not loose heat/cold. The other issue with sprayed in solutions is managing the life of the shingles on the roof. for SIP roofs, a 'cold roof' is installed which allows air to circulate under the shingles and controls their temperatures during the hot season.

Some folks spray foam directly to the bottom of the roof sheeting. I'm pretty sure this would void the shingle warranty.

My understanding is that Tyvek is permeable to water vapor, it is only impermeable to liquid water. If so, it would not be a vapor barrier.

Fred

 

[sands35]

My understanding is that Tyvek is permeable to water vapor, it is only impermeable to liquid water. If so, it would not be a vapor barrier.

Fred

Yes - I guess it's part of the "drainage plane" and is permeable to water vapor. Probably better to call it a water barrier, not vapor barrier. (though I didn't bother to look up what architects and engineers call it).

Just a note, in a house I used to own (built about 5 years ago). They had cellulose insulation on 2x4 walls. During *really* cold days, the master closet would have the dew point location about 3" inside the walls - which put it inside hanging clothing. (yay!) So they would get damp and cold for a few days. The closet had 2 exterior walls and no 2nd floor over the closet. So it was colder than the rest of the house.

 

[OverkillYJ]

I have concrete black walls and only two windows. I am assuming then that if I have it sealed up I will be fine? If not I just get some exterior stucco paint and put a couple of coats on? Wouldn't that stop vapor?

I thought a lot of it had to do with the speed at which the temp changes. I thought if I insulated the roof and didnt have air flowing in from outside I would be ok. No?