The roof on the log home has little or no insulation. I'm thinking new insulation between trusses right on the plaster and lath, new plywood and then tin.
Should I put a vapor barrier between the lath and insulation and then place a foam channel for air flow?
I would suggest that you use spray foam insulation. If you insulate the sloped section fully, so that there is no air movement, you will not need vents. Spray foam insulation does not need a vapour barrier. I have done a number of projects this way without any issues.
Vapour barrier should always go on the warm side of a wall or ceiling. Looking from the floor up-ward, it should be drywall (or whatever you plan for the ceiling ) then vapour, then insulation then some air space then your sheathing material (or logs if this is the case) then your exterior roofing material underlay (roofing paper or synthetic shield) then your metal or shingles or shakes ... what ever you desire.
Hope this helps.
Spray foam insulation sounds interesting, is there a name to the process and what is the material used, is it simular to the canned stuff off the shelf?
Spray foam is likely the best bet, it is a vapor barrier in itself, it is similar to the stuff in a can, but is applied through an airless gun out of a barrel, and has a more rigid finish.
This with a synthetic underlayment on top of the deck, should provide a great deal of barrier. The synthetic is a crucial component also, as the metal roof system will sweat inbetween the metal and the wood deck, depending on the style of roof you use, it may need to be strapped for breathing purposes also.
Good luck with the project, cheers !
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