ÓHealthy Living Spaces

• Build slab above grade. Exterior grade should be at or below level of sub grade, sloped away from wall at 5% (6 in per 10 ft).
• Install a vapor barrier on top of 6 to 8 inch clean, dry, coarse gravel  (no fines, no p-gravel) The suggested material is polyethylene plastic. The VB should be installed under the entire slab, lapped over the foundation/footing and sealed to the foundation wall. Monolithic pours: extend VB under grade beam to act as a capillary break. Insulating materials such as polystyrene are semi-permeable. When used under a slab without a VB, they permit water to dry to the exterior if the slab becomes wet from above.
• Do NOT put sand under or on top of a VB. The VB will still function with holes. If sand gets wet it will stay wet for decades.
• Use a good quality, low water-cement ratio concrete. Increasing the amount of water greatly increases vapor permeability and decreases concrete strength.
• Add control joints to concrete and cover joints with flexible caulk.
• Cure concrete by ponding water and covering with wet burlap. Cured concrete is less porous. Control the curing process and make it as long as possible (a minimum of 3-7 days).
• Install a capillary break membrane on top of the foundation wall (under the sill) or wrap damp proofing membrane from the sides of foundation wall onto top of foundation wall. This may act as a termite barrier also.
• Damp proof or install a moisture barrier membrane on the foundation wall from grade level to footer.
• Install French drains next to foundation using perforated pipes drained to a sump or below grade. Backfill with coarse gravel to grade level and place filter fabric midway. Waterproof coatings are NOT a substitute for a drainage system, as concrete and block are known to crack.