The basement is one of the most critical areas for improving building performance and a creating a successful DER. Colder outdoor air entering the basement displaces warmer air and forces it out of the house higher up. Fully air sealing the basement will eliminate the infiltration of colder air into it, and the neutral pressure plane (NPP) will then be further up in the building. The higher up the NPP is in the building, the better the house performs. Wind is another driver of infiltration/exfiltration and air sealing the basement will decrease its effect. Fortunately, basements are easy to insulate and air seal.We used closed cell spray foam for all of the basement walls, starting at the underside of the first floor, going over the rim joist and down to the floor. Where we installed new concrete floors, we brought the foam insulation down the wall to the drainage stone. We put two inches of EPS foam down on top of the stone, joining it to the wall insulation. The closed cell spray foam provided all of the control layers in one application. It does have to be painted with intumescent paint, or otherwise covered.
Any sources of moisture in the basement have to be eliminated. Any combustion equipment must be removed or converted into sealed combustion devices because they will no longer have access to adequate combustion air.