Converting attic to bedroom – Insulation & Venting Questions – GreenBuildingAdvisor

Greetings. I’m Spillers, a new member here and had a question about insulation.

I’m in a 1929-built craftsman home in climate zone 3A (Warm-Humid) and desire to enclose the attic to add additional bedrooms and a bathroom. The attic currently has blow-in cellulose on the attic floor and no insulation in the rafter bays or on top of the roof sheathing. The attic is currently vented by Gable Vents (there are no soffit or ridge vents); the roof is a 3-tab asphalt shingle. The rafters are 1 3/4″ wide by 6 1/4″ deep.

My current plan is to add soffit ventilation and cut in a ridge vent. I would create an air channel of approx. 1″ that would run from the soffit to the ridge (likely going to create a “sealed” air channel consisting of 1/2″ or 1″ foil-faced foam board affixed to furring strips nailed on this inside of the rafters and then seal the edges and joints with closed-cell SPF or tape); however, I have multiple hips on the roof which presents a problem venting from the soffits. 

Questions:

1. Non-Vented Bays (Hips): Do I spray closed-cell SPF in the rafter bays that cannot vent from the soffit to the ridge? Or, is my climate too warm for this “hot roof” effect?

2. Vented Bays: Do I insulate the rafter bays that contain the air channel (soffit-to-ridge vent) with batts or with closed-cell SPF?

        2.a. It is likely that I’ll go with batts over sprayfoam, as I’m aiming to perform the work myself – but I wanted to see if sprayfoam would be a better option to consider.

        2.b. If I use batts (either rockwool or fiberglass), do I go with the paper-faced facing the exterior or the interior, or should I use unfaced batts? I would follow either with a smart vapor retarder such as MemBrain, as I intend to finish out with wood and not gypsum board.

  

I am unable to create a new roof assembly complete with foam board, radiant barriers, and ventilation from the “exterior” at this time – so the best “interior” insulation option is what I’m aiming for.

Thanks,