Need Help with Converted Attic!
I am in the process of purchasing a 20 yr old colonial in Massachusetts and need some guidance regarding the roof assembly insulation. It is a production spec house with typical construction for the period. A later homeowner converted about 75% of the attic to living space and the remainder is just unvented and uninsulated crawl space. The underside of the roof is not insulated withe the exception I am assuming of the cathedralized roof in the living space. Also, there are very shallow (non-existent) eaves due to the fact that the style is early american colonial so it would be difficult to retrofit vents. The rafters are 2 x construction and with no insulation on the underside of the deck it’s not surprising that the asphalt shingles on the southern exposure are curling despite being less than 10 years old.
I am planning on installing HVAC equipment in the crawl space areas of the attic and have been planning on installing 6″ of CC SPF to the underside of the deck across the entire roof for an unvented hot roof assembly. My concern is that I just read Joe Lstiburek’s article on lessons learned from his barn retrofit and his admonishment about simply installing CC SPF to the underside (i.e. problem of thermal bridging). I do not have the inclination to install rigid foam to the top of the deck as this will incur gobs of carpentry labor expense reworking the eaves and rakes. Is it possible to use CC SPF in the rafter bays and then install 2″ foil faced to the underside of the rafters? I am also dealing with the issue of fire retardant as I am installing mechanical equipment in the unfinished portions of the attic. I assume that foil faced ISO would alleviate the need to paint the SPF or cover with drywall as an ignition barrier and offer thermal bridging protection. I understand that this is creating a vapor impermeable space in the assembly but I would assume it would not need drying. I would use dense pack with rigid foam but this will not get me to code with a net 7″ rafter.
Your help is greatly appreciated.
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