I am in the process of planning to finish the basement of my new (~2004) home in western Wisconsin. I've been doing a lot of reading on this forum and the Building Science Corporation and have learned enough to know that I need to learn more before making this investment.

My basement has a "lookout" wall on the north side with the rest of the walls being full height concrete. My neighborhood has sandy/gravelly soils but does have high groundwater which is normally about 2 feet below the slab. The builder did provide a sill gaskets and all sill plates are pressure treated.

For the floor, I'm going to do a test pit (I'm expanding the sump pit to fit a backup sump pump anyway) to see if there's insulation under the slab. If not, I'm going to go with vapor barrier, 1" XPS and 5/8" plywood or OSB. I'm also considering Delta-FL instead of the vapor barrier so that I'd be able to dry the slab without removing the entire floor (Tapcons and all) in the event that bulk water became an issue due to the high groundwater.

I'm far less sure about the walls. The builder installed a 2x4 stud wall around the perimeter of the basement held inside the concrete foundation by perhaps 1/2". He then installed fiberglass batt insulation and a vapor barrier (stapled to the face of the 2x4 stud wall). According to this forum and Building Science, this is not the recommended method. Instead, it it appears to me that best practices for a raw basement would have been 2" XPS or EPS board hard against the concrete with 2x4 stud walls set inside (with or without additional fiberglass batt insulation).

Unfortunately, I no longer have a raw basement so I am faced with two options: 1. Rip out the existing stud wall and replace with the best practices method mentioned above or 2. find an alternative that would allow me to leave the stud wall in place which leads me (finally) to my questions:

  1. Is spray foam a reasonable method to insulate below grade concrete walls? I can't find where it was discussed on this forum. Most literature that I've been able to find plays up the air tightness of the spay foam. I can't seem to find much information about vapor permeance. If so: Open cell or closed? What weight? What thickness?
  2. Is spray foam a reasonable method to insulate above grade exterior walls? I'm talking about the upper part of the lookout wall and the joist bays. If so: Open cell or closed? What weight? What thickness?

Thanks in advance for your replies!