Finishing a below-grade concrete basement requires understanding psychrometric moisture drive: ground moisture continuously diffuses inward through porous foundation slabs and walls.
1. The 3 Invariants of Basement Wall Assemblies
- Continuous XPS Foam Insulation: Minimum 2 inches of Extruded Polystyrene (R-10 XPS) glued directly against foundation walls acts as a continuous thermal barrier and Class II vapor retarder, preventing warm interior air from condensing on cold concrete.
- Air Gap Between Framing & Foam: Non-load bearing stud walls are built 1/2 inch away from the rigid foam face to isolate wood framing from any thermal bridges.
- Dimpled Polyethylene Subfloor (Dorken Delta-FL / DMX): Creates a continuous 5/16" air gap above the concrete slab, allowing concrete vapor to breathe and equalize without soaking finished luxury vinyl plank (LVP) or carpet.