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Making room in attic, insulating rafters?


BombThreat's Avatar
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11-01-04, 07:41 PM   #1  
BombThreat
Making room in attic, insulating rafters?

Hey guys, I see there are alot of people asking about insulation attics here. I read a few and thinking my situation is a little diffrent from others so making a new thread seems like the best option. Anyway, I was wondering what kind of insulation to use on the exterier wall, the rafters, and a interier wall. With the floor already having blown-in insulation. I live in upstate NY so temps get to about 0 - negitive 5 degrees at the lowest. I remember reading about vapor ventilation, but I don't exactly understand how it works and what the matierials looks like. If anyone knows a diagram that would be great. Thanks guys

-Scott

 
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Pilot Dane's Avatar
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11-07-04, 04:34 PM   #2  
It sounds like you might be double insulating. The floor of the attic is insulated and you want to insulate the roof?

Basically you want a vapor barrier right next to your heated living space. Everything you do in the house like bathing, cooking & breathing puts moisture (water vapor) in the air. You don't want that water vapor to pass through your walls and encounter the cold. Cold temperatures will condense the vapor into liquid water which is bad for your insulation and wood.

You do not want two vapor barriers. If any water vapor gets past the first inner barrer you don't want it getting trapped. It should be free to escape the house. Many older homes do not have much of any vapor barrier so it's probably best to avoid putting any new barrier in the attic. You could probably use unfaced fiberglass batts. These will insulate while letting the moisture pass through.

There is one downside to insulating your roof rafters. You want your roof & shingles to have good ventilation from below. This helps prevent rot in the roof sheeting and the ventilation cools the shingles extending their life.

You might want to have an insulating contractor in to look at your house. They can offer some good advice, and they may be quite reasonable. When I built my house two years ago I could hire the insuation installed cheaper than I could go to Lowes and buy the materials and I didn't have to do the work.

 
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