Below-grade waterproofing prevents water intrusion through foundation walls and slabs. Systems: (1) Sheet membrane (self-adhering modified bitumen): Carlisle CCW, W.R. Grace Bituthene, Henry Blueskin. Applied to primed concrete, minimum 40 mil thickness, lapped 3-4 inches at seams. Most common for residential. Cost: $3-6/sf installed. (2) Fluid-applied: Polyguard 650, Mar-flex 5000. Spray or roller-applied, seamless, 60 mil minimum DFT. Better for complex geometry. Cost: $4-8/sf. (3) Bentonite clay: Cetco Voltex, Tremco Paraseal. Geosynthetic clay liner, self-healing if punctured. Cost: $3-5/sf. Code: IBC 1805 requires waterproofing (not just dampproofing) where hydrostatic pressure exists. Dampproofing (asphalt coating per IBC 1805.2) is acceptable where no hydrostatic pressure. Drainage board and perimeter drain required in addition to membrane. Warranty: 10-25 years depending on system. Inspection: before backfill — this is a HOLD POINT.