Dimpled sheeting is similar to a small egg crate and permits free drainage down the wall and across into the drain pipe. It is less expensive than many specialized drainage channel systems. In low permeability soils, this system cannot accept rising groundwater unless there is an aggregate layer under the slab. A polyethylene vapor retarder is placed over the foundation wall before installing finishes. No interior vapor retarder should be placed over batt insulation when finishing walls if there is already a vapor retarder on the foundation walls.
Rigid insulation is placed on the floor and then covered with a decay-resistant plywood subfloor.
Another approach to making the basement dry for interior finishing follows. The sheeting serves as a vapor retarder and it forms a drainage layer connected to the drain pipe below. This is particularly effective if the wall is to be finished. A second interior vapor retarder should be avoided, however, if batt insulation is used. The dimpled plastic sheeting can also be placed over the floor and covered with rigid insulation and a tongue and groove plywood subfloor.