Basement – How to insulate exterior basement wall

Why would you need insulation on the ceiling in a basement? Since the ceiling is touching a heated space itself, there is no need if you will then be using the basement too. Insulation there should be done only for soundproofing, unless you have radiant underfloor heat installed, in which case, the insulation should have been done already as part of the installation. So insulation really only offers soundproofing value. So the question is, how much noise will be generated there?

Counterbalance that with the rationale for leaving this space accessible. I've often enough needed access to the underfloor regions of my home, for wiring changes, plumbing changes, repairs, etc. So any insulation may be better done as fiberglass batts anyway.

As far as the walls go, filling the cracks is a reasonable idea, IF they are stable. If the walls have moved due to frost heaves, etc. and might continue to move, I would ensure they are stabilized before you cover the wall over. A buckling foundation wall is not something good to have under your house.

There is a rigid polyisocyanurate foam core insulation, often sold under the brand name Super Tuff from Dow that has a higher R value than XPS. It is R-13 in 2 inch panels and is higher if you trap a small air barrier behind it (around R-15).

The foam has a foil vapor barrier on the back.

You could

• mount this on the existing furring foil side out, using glue and screws
• seal the edges with foil tape
• reinstall paneling with glue and screws throught the foam, into the existing furring.

HOWEVER: The paneling could hold itself up when mounted this way, and you could mount lighweight things, such as pictures. The walls would NOT be suitable for mounting shelves, fixtures, heavy mirrors, etc. You would need to take care and inform any subsequent owner that the walls were not intended for bearing any signifciant weight!