The ceiling is open through the rafters up to the roof. I love the ease and convenience of storing things in the rafters, but we will put up a ceiling and insulate it.
Keep it open if you like it. Spray foam the roof deck and keep the open trusses. Nothing wrong with that.This is incorrect. Do not spray foam directly to the roof. Ventilation is needed to keep it cool underneath the roof. Ice dams are a major concern if you heat the entire space. I have a friend who used the spray foam directly to the sheathing and he fought ice dams every year since.
The proper way to insulate is to apply vapor barrier, then rock the lid. Next install baffles to allow air to circulate from the soffits and out the roof vents.
^^^^^ Here is a perfect example of an incorrect installation of foam ^^^^ Clearly the wrong R-Value was applied.
The best practices we have found over the last 35 years of building homes have been directed by BSC. When Building Science Practices have been followed, we have NEVER encountered a failure.
https://buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates