I am bidding a roof framing job for a client. My problem is the new code for ceiling insulation in my area is R-49. This has to be stick framed not roof trusses. I was thinking of building the ceiling joist system, as if with 2×12’s @ 11-1/4″ in height framed more like a floor system with rim joists, not placing any plywood decking. Then adding a 2×6 plate picking up another 1_1/2″ over rim board/joist ends and cutting a 5″ height over plate in the rafters giving a total height over plate at rafter ends of ceiling of 17_3/4″ for R-49 over wall plate and enough for a Styrofoam insulation baffle. One question is due to the rafters just anchored to the added plate I believed I would have to then add a rafter tie in the bottom 1/3 of the height to ridge area on 4′ centers to stop the rafters from pushing out at the plate from snow loads. Am I correct or does someone have a better technique.

Thanks, George M. Morio Builder