I am planning to insulate the basement of my row house. Given that I'm in Region 5, I will need proper insulation on the exterior-facing basement walls. But what about the walls facing the neighbors? As far as I know, we're either all in the same poured concrete foundation or their foundations are separate but directly adjacent - there is definitely no gap between the houses (see Figure below). The basement is 100% below grade in the back and approx. 70% below grade in the front (where the door & windows are located).

I could not find any good guidance on my exact situation anywhere. Are there code requirements (I'm in Boston/MA) and/or best practices for these side walls? Specifically:

  • Do they need any kind of insulation? If not by code, would it still be recommended? How much R-value?
  • Should I frame along the wall with studs, or can I install furring directly on the wall?
  • What should the corner transition between exterior wall and neighbor-wall look like (insulation, sealing, etc.)

On one side, my neighbor's basement is unfinished, on the other side it is finished.

Drawing for reference (the light grey areas to the left and right side of the walls represent the neighbors' basements, which have identical geometry):

enter image description here

  • On the shared walls, between you and your neighbours is there any form of insulation or board already? – J Crosby Jun 26 '19 at 20:27
  • No, it's just the naked concrete foundation all around, completely unfinished. – J. Becker Jun 26 '19 at 20:47

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