In our last post we addressed the floor in a basement finish in Philadelphia. Now we're going to turn our attention to the walls: We recommend covering all the walls — both party walls and front and back — with 3 inches of closed cell (2-lb.), soy-based spray polyurethane foam. Leave any existing dirt and debris on the basement walls before spraying, as it actually helps to break up the continuous bond. Let me explain.
A very common mistake is to assume an impermeable membrane, such as rubber, is the appropriate solution to basement water problems. In fact, by trapping the moisture on one side or the other, you end up either with a damp basement or water trapped in your concrete foundation (not a good thing).
The idea is to let the water come in, then drain between the spray foam and the foundation, where it runs down to the drainage mat, to the sump pump, and out of the house. That's why you want the spray foam to stick to the drainage mat at the bottom of the wall and tie into the floor framing above, but not to fully adhere in the middle. The other benefit of all this spray foam is you end up with a super-insulated basement.
When framing the basement, we'd use 1-1/2 inch metal studs covered with drywall, which also provides fire resistance (if you're not finishing the space, you can just use intumescent paint applied right to the foam). If the plans call for vapor barrier, I would recommend a 6-mil polyethylene sheet which has a relatively low thermal mass, again minimizing condensation on one side or the other.
One last point — if you're considering finishing a basement, I would highly suggest looking into an appropriately sized air exchanger down there. This equipment can do wonders for air quality, mold prevention, moisture minimization, auto-immune disease prevention, etc.
Phew. That's enough tech speak for one day. Next week I'm going to post a brief treatise about foundations for detached homes, one which many clients have found invaluable.