Insulating 2x6 rafters in finished attic

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Old 04-23-09, 01:50 PM
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Insulating 2x6 rafters in finished attic

I'm finishing my attic. I have 2X6 rafters in which I'll need to insulate. I understand I need to put in baffles to allow for air flow. What is the maximum R value insulation I will be able to put in the 5 1/2" deep cavity combined with the baffles. My thinking was put in: baffles->r-19 unfaced insulation then cover it with Reflectix foil. Is that a good plan, or should I consider R30? Does the Reflectix provide the vapor barrier as well or am I totally missing the point?

I've also heard of people adding furring strips to increase the cavity depth, but space is limited as it is, so, I'd rather not do that.
 
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Old 04-23-09, 02:27 PM
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dealing with 5 1/2" doesn't provide a lot of insulation. baffels or a one inch air gap won't move a lot of air, but going with that only leaves you 4 1/2", or about r=15 for fiberglass. Going with solid polyisocyanurate at r=7 per inch will give you about r=31, getting closer. Add another inch across the inside before the drywall and you cover some of the thermal bridging and add another 5 to the count.

Here is a link to read for additional considerations:
Welcome To Home Energy Magazine Online

Bud
 
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