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Community and Q&A

Insulating above grade concrete walkout basement wall

agm413 | Posted in Energy Efficiency and Durability on

Hi Everyone,
I am located in climate zone 4, close to 5 – North NJ near NYC.

attached 2 pictures, one from inside, other from the outside of above grade foundation walls.

I am wanting to add some insulation to either the interior or exterior (both?) of these walls since they can get very cold in winter and medium warm in summer. 

2 questions: Would exterior insulation be worthwhile since I can’t insulate all the “thermally bridged ” area of the concrete.  only about 30% of the wall on the inside would get insulation directly on the outside, while  the rest of it is under the stairs/the adjacent wall.

If interior insulation,  do I need to insulate the adjacent wall which is technically not an exterior wall since it attached to a rowhouse on the other side?

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  1. Expert Member
    Josh Salinger | | #1

    Hi agm413,

    You are on the right track with the difficulty of insulating on the exterior of your home due to the reasons you pointed out such as the stairs and (potentially) needing to excavate in other areas. It would also be an additional expense to finish the exterior insulation and protect it. For these reasons, the interior seems to be the better approach.

    I would refer you to Martin Holladay's article on GBA "Three Ways To Insulate a Basement Wall":

    I would recommend insulating the partition wall as a part of this. I'm guessing it is the same condition on the other side which is in effect unconditioned space. Creating a continuous thermal and vapor boundary is important when insulating basements.

    I would also address the garage door as this would be a weak link in the thermal boundary and air barrier. Thermacore offers some good options for insulated garage doors.

    Best of luck!

    1. agm413 | | #2

      Thanks for reply Josh!

      I need to air seal the top of the garage door a bit better. There's a decent amount of air leakage there - that's on the list. Also insulating the joists, but those are covered by drywall for fire safety and also have wires running along them + the garage tracks. Should I also insulate the ~12 inches on cement on the sides of the garage door that are also uninsulated like in the first pictures?
      the basement of both these houses is in the conditioned space and that partition wall between them is actually a foundation cement wall - better picture attached of the wall near the stairs between the houses.

      Edit: Also insulating around the inbound pipes will be tricky, and finishing in front of them with something that also gives access.

      Basically just trying to figure out what to insulate since 2 of my long cement foundation walls are attached to other houses garages (on the left) and basement little area (on the right). But it seems like interior side all the way around, and not the wall between my garage and this area is the way to go. Also the issue of not being able to get to some of those areas if they're behind stair stringers and/or drywall on one of the sides

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