I'm remodeling my attic in my bungalow, the way I want to do it is to leave the rafters exposed so I get a rustic loft look. What I done first was put wood strips up between the rafters then installed the flat foam insulation onto the wood strips so there was a expansion cap between the roof and the foam insulation. Then I put up the 3/4 drywall between the rafters. Now I'm doing the taping on those inside corners of the drywall between the rafters My Question Is,,, because one side of the drywall mud and tape will be on the rafter when we get our extremely cold winter weather even though the attic will be heated can those rafters freeze and cause the corners to crack.
Since the wood is apt to move a little, I suggest you use "tear away bead", and maybe apply some painter's caulk after a season if you see any gaps. The alternative would be flat taping, but that depends on a pretty close fit between the drywall and the timber.