What is the best way to superinsulate a walk-out basement?
I need an expert’s opinion of my current and future game plan for my Upstate NY – Zone 6, 1968 back-split renovation.
Q1: Can I safely add 4″ of exterior poly iso, since I will already have 3″ of closed cell on the interior of the wall?
Q2: How can I improve this plan?
See plan details below.
My first project will be to insulate and finish the lower level (41ft X 12ft). Two sides of the space are partially exposed (between 1.5 to 3.5 feet below grade). Third wall faces a semi-conditioned garage.The fourth wall backs up to a ventilated dirt floor crawl space. All walls are block (~4ft) and 2×4 framing (~4ft + 12″ joist space for 2nd floor).
Crawl space – Insulate two exterior walls + wall facing garage with 3″ closed cell spray foam. Remove ventilation and existing insulation between the overhead floor joist.Wall facing lower level will be left un-insulated.
Also, install 6 mill ply on floor. Eventually poly will be augmented by concrete floor.
Lower Level – Frame out using 2x4s all exterior block walls (two sides).
The third wall facing garage is already 2X6. Fourth wall facing crawl space will be left uninsulated.
Insulate all three walls with 3″ closed cell.
Insulate concrete floor with 1″ rigid foam + plywood & finished floor.
Rear cantiliever (1.5ft x 71ft) will be opened and insualted with 4″ of closed cell
Future plans for the house include adding 2 layers of 2″ polyiso to the exterior of the building including the lower level. This will also involve residing the bouse with either fiber cement or reusing existing cedar siding.
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