Definition
Footing drainage is a system installed at the base of foundations to collect and redirect water away from the structure. It typically consists of perforated pipe (drain tile) surrounded by gravel, placed alongside the footing. Proper footing drainage prevents hydrostatic pressure buildup, basement flooding, and foundation damage. The system should outlet to daylight, a sump pit, or a storm drain.
Formula
For proper drainage flow, maintain a minimum slope of 1% (1/8 inch per foot). A 4-inch diameter perforated pipe can handle approximately 10-15 gallons per minute per foot of pipe length under normal conditions. Use 3/4-inch crushed stone around the pipe for proper filtration.
Example
Drain Installation Example
Install 4-inch perforated PVC pipe at the footing level, surrounded by 12 inches of 3/4-inch clean gravel. Cover with filter fabric to prevent soil intrusion. For a 40x60 foot building, approximately 200 linear feet of drain tile is needed (perimeter). Ensure the outlet discharges at least 10 feet from the foundation.