Well there are numerous methods, but the best one would be to go with a "hot roof" by either spraying directly against the roof deck or adding foam above the sheathing. Personally I would leave the interior open if you go with some nice looking wood & add foam above For More: http://blog.sls-construction.com/2011/what-is-a-hot-roof
How to insulate a cathedral ceiling with no ridge
How to insulate a cathedral ceiling with no ridgeAsked by Tom
I am building this 5 sided office studio that has a cathedral ceiling http://www.summerwood.com/products/home-studios/catalina/1045/detail.html The roof is built so the rafters all converge to a 'hub' , so there is no ridge. I am planning on sheet rocking the inside to cover the rafters. I would love advice on how best to insulate the roof. Thank you in ad ace for your help!