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brendaliz 09-05-2012 11:31 PM

Confused about Unvented Attic Insulation
We own a 1903 house in western Maryland (zone 4?). The house has an existing unvented attic with plenty of room 50 x 25 with roof about 7 feet at peak) It is accessible by a large staircase and there is an air handler unit that feeds the floor below (heating and cooling via heat pumps). It has two large gables with small windows. There is no existing insulation, floor is covered by boards over 8" joists and roof rafters are 9" deep. From all we read, maintaining a unvented attic makes sense - assuming good air sealing around perimeter and the right insulation. Given cost of spray foam, are there any allowable options using fiberglass batt insulation? One person suggested a baffle (to keep an air gap) and then fiberglass. Is this allowable or recommended as it relates to moisture problems? Roof has asphalt shingles and a wood deck. Any thoughts would be appreciated.

jklingel 09-06-2012 01:10 AM

FG batts are poor insulation, but cheap and ubiquitous. If you must use them, then, yes, vent behind them and air seal as you mentioned. Try to find Roxul batts, and vent them, too. Another option is to install rigid foam boards (tape and goo edges) and sheet rock over that, venting behind them.

Windows on Wash 09-06-2012 07:38 AM


Fiberglass batts just won't get it done in this scenario as they have questionable R-Value in unvented applications and even less in vented applications.

Spray foam would be easiest and most straightforward but would also be the most expensive. You could do it with a combination of rigid foam and fibrous insulation.

All depends on what you want to do with the space at the end of the day.

brendaliz 09-09-2012 09:21 PM

Thank you for the replies. Our more immediate goal would be storage. But we see the possibility of finishing some of the space given the main staircase goes right up to the one portion of the attic. Could you elaborate on the options using rigid foam?

AndyGump 09-09-2012 10:27 PM

Having a hard time understanding...ah...anything about your situation.
The staircase (open staircase I presume?) goes up to the attic area and the floor of the attic area is 2x8 sheeted (no insulation?).
The roof rafters area open (no drywall) and/or insulation?

You want to use the area as storage only but maybe at some time build a little living area up there?

Odd situation to say the least.

Sounds like you should have a contractor or designer give you a hand with what you want to accomplish in this space.


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