[70SATMan]

I've got a typical 1961 Cal ranch house on the Central Coast. 2x8 T&G Fir open beamed roof. 4x6 beams on 6 ft centers. So, of course no roof insulation. The original roof was tar and gravel which sucked balls and we replaced it with 30 year asphalt shingles. The exterior roof insulation was very expensive at the time so, we opted out of that.

We want to insulate and drop the ceiling down to cover the rafter beams so that I have enough clearance for installing recessed lighting throughout. We've never had soffits or ridge vents and based on the condition of the roof when we re-roofed, decided we didn't need them. That was with the open ceilings.

SO, looking for advice on the insulating material. While most of the info out there recommends air gaps, there is thought that in a situation like mine, no gap is better. As long as the vapor barrier is to the living space. Would you recommend rigid foam or fiberglass batting? The fiberglass would be easier to install lighting but, I may be able to get better R out of the foam and then deal with the cans into it. Also, I'll be attaching the electrical wiring to the underneath of the roof T&G.

Last but not least...Over the new interior insulation will be 1x6 T&G wood. No rock. So, do you think the 6 ft centers of the rafter beams is to long of a span? My gut tells me it'll sag. Should I just bite it and add additional nailing strips? The new nailing strips would need to be 2x6 on edge to block the open areas out. Can't imagine that 3 ft centers would sag..