Water exerts about 0.43 psi for each foot of depth, so a basement 20 feet below the water table sees roughly 8.7 psi on its lowest slab. Under constant pressure, water finds every crack, cold joint and tie hole. Systems for hydrostatic conditions must be true waterproofing with sealed laps and details; dampproofing is not enough. Drainage that lowers the water level reduces the pressure.
Water table's above the slab, so there's real hydrostatic pressure, dampproofing won't cut it down there.
The design water level in the geotechnical report decides between dampproofing and full waterproofing, so read it before choosing a system.
Also heard as
- hydrostatic head
- head pressure
Related terms
Dampproofing
A thin coating that slows soil moisture through a foundation wall but cannot resist water under pressure.
Positive side
The face of a wall or slab that touches the water source, where waterproofing works best.
Drainage composite
A dimpled or ribbed plastic core with filter fabric that carries water down to drains instead of letting it sit on the membrane.
Waterstop
A strip cast into concrete joints to block water from traveling along the joint plane.