Installing polyethylene under a concrete footing prevents ground moisture from wicking up the basement walls.
In preparation for pouring the basement slab, a layer of 1-inch-thick polystyrene insulation is installed over 6-mil polyethylene and 8 inches of crushed stone.
The key to the author’s airtight shells is the continuous vapor barrier, which starts beneath the mudsill. Every seam is taped or sealed with acoustical sealant.
Before installing the mudsill, a 6-inch-wide strip of poly is embedded in Tremco sealant and stapled to the underside. A 2 3/4-inch-wide strip of foam sill seal is stapled over the poly, and then the sill is flipped over and bolted in place. The poly flap faces the exterior.
The band joist is wrapped with Tenoarm, a very tough, transparent polyethylene. The Tenoarm has been taped to the white polyethylene stapled to the bottom of the mudsill, and then wrapped up onto the subfloor.
After the walls are raised, the transparent Tenoarm polyethylene sticks out from under the bottom plate, facing the interior. This flap will later be taped to the wall poly.