need thin, high R value insulation ideas

We have a vaulted ceiling with knotty pine wood. It turns out there is no insulation! There is no space between the knotty pine and the roofing material. We don't what to lower the ceiling anymore than we have to. What's our best options? Thanks, Mary

 

In a similar situation with a log cabin home, I used logs for rafters 24 inches on center. Then I installed tongue and groove pine boards on top of the rafters. Then installed a 8 mil thick vapor barrier that overlapped and taped the seams with a vapor barrier tape. On the rakes, ridge and rafter tails I used lumber to give me the desired depth for the insulation. In my case, 8 inches for a R-40 using rigid board insulation in 4 x 8 feet sheets, 3 inches thick. One layer was 2 inches thick.

I laid the insulation in the field and staggered the layers so the seams would not line up and taped the seams on each layer. Then installed 3/4 inch plywood over the insulation using 12 inch screws 24 inches on center into the log rafters. I made sure that the lumber on the rakes was set to be a 3/4 inch higher than the plywood and on my rafter tails and ridge at a height of the insulation so the plywood would be nailed to it.

Then I nailed 1 x 2 inch wood slats 16 inches on center from the rafter tails to the ridge. Then installed 3/4 inch plywood over the slats. This created 3/4 inch gap between the layers of plywood from the rafter tails to the ridge. On the rafter tails I installed a drip edge vent to cover the gap at that end, installed the roofing shingles and when I got to the ridge I installed a ridge vent.

 

LOL, I'm wore out after just reading that