Insulating basement in Boston area – GreenBuildingAdvisor

Hello,

I will be insulating my basement walls to add some basic livable space. 1920’s colonial with poured concrete walls and floor, very dry with no water intrusion, efflorescence etc. Basement is about 75% below ground level.

Looking at the 21 and 24 IECC code, for a basement wall in my zone (5a),

“15ci or 19 or 13&5ci” – “…. means R-15 continuous insulation on the interior or exterior of the wall, or R-19 cavity insulation on the interior side of the wall, or R-13 cavity insulation on the interior of the wall in addition to R-5 continuous insulation on the interior or exterior of the wall.”

– I’m planning to do 1″ foil faced polyiso (R6) on wall + rockwool (R13) in 16″ OC studded wall butted up against foam board + sheetrock. I was reading on here about the long-term differences in insulation value between ISO/XPS/EPS, but thought that the foil faced ISO would work.



My questions are:

– Although it meets code, is R6 foam board sufficient, along with the R13 rockwool?

– Any potential future issues with condensation that would be mitigated with going to 2″ now?

I know that meeting minimum code does not always mean best practices.

Thanks for any thoughts and suggestions.

John