Foundation drainage: footing-level perforated drain pipe, gravel envelope, daylighted discharge
BASC Guide — guides/foundation-drainageDescription
Below-grade foundation drainage prevents hydrostatic pressure + moisture intrusion: a perforated pipe (4 in PVC or HDPE) installed at the footing level, surrounded by ≥ 6 in of clean ¾-in gravel, wrapped in filter fabric, sloped at min 1% to a daylight discharge or to a sump pump. The drainage system + the foundation waterproofing membrane on the exterior wall work together — neither alone is sufficient.
Why this exists
Wet basements + crawl spaces are 90% caused by missing or under-built foundation drainage. The detail is cheap to do right at construction; expensive to retrofit later. Architects should call out the perimeter drain on the foundation section, including the discharge location.
Categories
Source
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Continuous load path from roof to foundation · HUD RSDG §2.4
- Residential structural reliability targets 1-in-100 to 1-in-1000 annual probability of failure · HUD RSDG §2.5
- Residential floor live load: 40 psf minimum (30 psf sleeping rooms) · HUD RSDG §3.4
- Wind load design uses ASCE 7 basic wind speed for the locality · HUD RSDG §3.6
- Ground snow load for Virginia: 25 psf eastern, up to 40 psf western mountains · HUD RSDG §3.7
Last reviewed 2026-05-15.