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bgent 05-19-2012 06:58 PM

Insulation to fit between 4-inch rafters
After we knocked out a chimney and our kitchen ceiling for a home remodel, we discovered a relatively roomy attic space above the kitchen, which we are now finishing so we can make use of it. However, right now there is no insulation between this attic space and the roof. I want to change that before the hottest part of summer arrives. :)

The rafters are 4-inches deep, meaning we can only have insulation about 4 inches thick. A building inspector who was checking off part of our project told my wife that there is some kind of foam insulation that would fit in that space but still have a pretty high R value... But so far we haven't had any luck finding anything that will do the trick.

I'm currently considering a combination between some kind of foam insulation and radiant foil to help shield the new room from the worst of the sun's heat. Could this work?

I'd like to hear any other suggestions on how to insulate this area. Thanks!

Windows on Wash 05-19-2012 10:18 PM

Radiant foil needs an air space to work.

Rigid polyiso is going to have the best R-value but still won't be adequate at 4".

You will need to look critically at the venting as well and moisture control.

joecaption 05-20-2012 05:46 AM

Is this space even able to be converted.
By far most attic were never designed for use as a living space or even storage space.
The biggest issure is the width, spacing and span of the joist.

There needs to be a ridge vent, soffit vents, baffles for air flow from the soffits to the ridge vents before any insulation ever goes in. With just 2 X 4's that would only leave room for 1" of insulation.

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