Finished basement perimeter wall — foundation, rigid foam, stud wall, batt, drywall, and rim-joist air-seal
A finished basement wall is a layered assembly built inboard of the concrete foundation: continuous rigid foam (R-5), a 2×4 stud wall off the concrete, unfaced cavity batt (R-15), and ½″ drywall + paint. Two basement-only details — a pressure-treated bottom plate where wood meets the slab (IRC R317.1) and a closed-cell rim-joist air-seal — are what make it dry and tight. The composer counts studs, batts, sheets, and gallons from this one wall.
What this diagram shows
A section cut through a finished basement perimeter wall, drawn outside to inside. Against the soil is the existing concrete foundation wall on a footing, most of it below the grade line. Built inboard of the concrete is the finished assembly: a continuous layer of rigid foam board rated about R-5, then a 2-by-4 stud wall at 16 inches on center standing off the concrete, with unfaced batt insulation rated about R-15 filling the stud cavities, and half-inch drywall with paint on the room face. Two details competitors bury in prose are called out: the bottom plate resting on the slab is pressure-treated because wood contacts concrete, required by IRC R317.1, and at the top the rim joist where the floor above meets the foundation is sealed with about two inches of closed-cell spray foam for an air and vapor seal per Building Science Corporation. A numbered key labels all seven layers. Framing, insulation, drywall, and paint are all sized off this single wall.
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