What is the best way to insulate a below grade, outside wall in the basement ??

Answer 1

fisrt water seal the masonry with a QUALITY trowel applied asphalt product [karnack is a very good brand] it will be Much easier to apply and last much longer if you take the time to 1st paint on an asphalt primer. you can then [opptional] cover this with a plastic sheet [ visquine] or ridged asphalt board. then use an r6-9 poly foam insulation board made for below grade use and back fill with rich soil /compost... not sand! this will keep water from draining too fast a nd entering your foundation fron underneath the floor. all materials should be available at a "supper" home center, masonry supply, or building supply wholesale/ distributor.

Answer 2

Dig down to the footings then apply a waterproofing compound to the basement wall.
Insulate the walls with high density Styrofoam. The thickness will be determined by how much protection you need. It is measured in R Value. Your lumber yard will be able to assist you with this.

Answer 3

Use spray foam it's the best, having a company do it will guarantee the job.