Fellow Architects,
I am a retired Architect who own a historic Jail building built in 1825.
After 103 years of abandonment and complete neglect (except for my 33 years ownership) I'm converting it into a residence. To make it more livable I'm adding a one story addition.
My question is about how to insulate the attic.
Most of the the slate roof has been repaired by installing new sheathing where needed, removal of the remarkable Swedish Iron nails and relaying with copper nails the Munson Maine Slate ( a product with a long lifetime ) .
Advice I'm receiving here is to install a closed cell urethane spray foam insulation on the roofs woodwork and not the floor.
While this yields an attic that can house mechanical equipment and possibly interfere with the post beetles if they still are working, I am worried that this sticky application will make future roof repairs impossible. Leaks from above would cause rot that would be very difficult to repair. And ruin the original remarkable woodwork,
Important whether seen or not.
This structure, designed by Stuart A. Park , a powerhouse architect of his day, deserves the best solution.
What should that be?
Please advise,
Charles Griffin
Architect
MA