Hi, I'd appreciate all your wisdom to be sure I'm on track. I know nothing about actually DOING renovation work--and Youtube and Chat can take me only so far! I am acting as if I am the general contractor for "Our Guy" who actually does the work. He is multitalented (most skilled in carpentry and mortar). I try to stay ½ step ahead to help choose materials, watch out for toxic stuff, etc.
Lots of background details first, please be patient. The questions will be about insulation and wood protection mostly.
Our home is in northern Virginia. We are seniors and the house is probably a knock-down. Our Guy is doing long overdue remodelling for us so we can 'age in place'.
We have a flat roof with virtually no insulation. The underside of the plywood deck was sprayed with sort of a popcorn finish, and that's our ceiling. It is currently a DuroLast roof (pvc) over bitumin or similar. I have loved it but after 25 years it is brittle and fragile.
I believe there was water intrusion before the DuroLast roof went on, but possibly some water came in after. The roof membrane was not welded to the inside of the gutter, there's a loose fascia board, and some missing flashing. We intend to address them all as best we can.
The current gut reno of a section of the house means the roofers can remove and replace some rotten plywood deck, and add 1" polyiso insulation over the whole roof. I know there is more rotten plywood up there but don't wish to pull the entire roof off, for $anity's $ake.
Is it ok for the roofers to use pressure-treated ply in the roof decking (off-gassing, our health)?
Big question: Is 1" of insulation above the deck sufficient? I am planning to (carefully) do a interior DIY spray foam (closed cell) insulation with Our Guy--a thin 1" layer, seal any air gaps, avoiding anything we don't want buried like ducts, electrical, plumbing that would be hard to dig out of dried foam. I would follow it with 3" rock wool (rigid foam insul if I win the lottery). I figure that gives R 19 inside and R 7 outside.
I realize this is far less than the recommended R 30 + but the insulated section will only be ⅓ of the roof and the house has big single pane window and lots of air permeability.
Am I wrong to use spray foam (off-gassing)? Am I wrong to do this amount of exterior or interior insulation?
We are tearing out rotten wood inside (some 2 x 4s, some ply subfloor). Before new wood is installed, I plan to pretreat it with Penashield borate fluid to discourage termites, ants, fungus and wood decay. Should I consider engineered or cedar 2x4s instead?
We are spraying Concrobium on mold as it's found. The beams, joists, and structural stuff is sound, even though we needed to treat for termites in the past.
What do you think of this plan?
Thank you, thank you, thank you, nerding out over here,