Porous concrete foundations should be treated to avoid water seepage into the home. Builders treat below-grade walls with a damp-proof coating such as an asphalt emulsion. For more reiorous protection, a plastic drainage plane may be used instead of, or in addition to, the damp proof coating.  This surface coating may be joined by a layer of insulation. Rigid fiberglass allows water to drain through it; rigid polyurethane foam rated for soil contact is another option. A gravel layer is added to provide a good backfill for draining. This allows water to flow through the gravel toward the foundation footing where a perforated drain pipe will carry it away from the structure.