Lots of good info you guys..and just so you realize, going to be doing all the work myself. I do my own gas/water plumbing, electrical, framing, dry wall (though I hate it). I've done complete roofing with my father but, I had mine contracted because I have a flat roof carport and didn't want to mess with installing the membrane so, I left the roof to the pros.
However, I'm 10 yrs in on a 30 year roof so, I'm not going to re-roof unless we go up with an addition. At the time the additional weight of the foam/OBX sheathing needed for the exterior insulation route gave me concern with the 6 ft OC beams. My roofing contractor felt the same. The cost delta at the time was substantial as well.
Island....interior 10 ft beam span. Also, the ridge beam is supported in the center of this section of the house (behind me in the pictures) by a full 3/4 masonry fireplace wall 3 ft thick that runs from the crawl space (with it's own footings) all the way up to the roof line. On the back wall is an open walkway from the dining area into the living room. Our climate here on the Central Coast is nearly Mediterranean.
At any rate, my place is an L shaped layout wrapped around my carport with only the backside of the house utilizing the open beam roofing. Of that open beam section we only really see one half of that in my dining room/office and a little more than half in my living room. Interior walls and drop ceilings cover the rest so, it's not like I'm covering a ton of detail and it'll still be cathedral when I'm done. At this point we have new track lighting on the ridge beam in the living room...That'll stay. We haven't settled on the dining area lighting yet but, I only need two cans in the office which is off the dining area.
Couple of pics:
Living room
Dining area looking at the new office:
It'll be easy to add the additional nailers for the new T&G. Tying that into the ridge beam and the exterior wall top sill plate will alleviate weight concerns for the new interior ceiling. I was just trying to avoid more work, heh heh.
Pretty much knew the answer to the question when I asked it...Just need you guys keeping me honest. Going to go with 24"OC.
If I go foam, I will only use the Dow Thermax. It's foil backed both sides and rated for exposed use so, no need for rock over that as an additional barrier. I'm more than comfortable going right over it with the new finish T&G ceiling. Even though it's more expensive, I get R26 for four inches over R15 with fiberglass batting and that's without dropping the ceiling any lower than the beams (plus the 1" T&G).
I have enough room right now with the Thermax to get a 1 inch air gap.
My biggest question still is whether I really need the air gap with either insulation type since I don't have soffit or ridge vent air flow. If its safer to have it than not, then I just have to space the foam down with furring strips. If I stick with FG batting, then I'm going to need to drop the entire ceiling down to get an air gap and then I can get R19 up there.
Keep the comments/suggestions coming...good or bad...Its all good...
