Foundation Waterproofing Drainage Calculator

Calculate drainage pipe capacity, gravel backfill volume, waterproofing membrane area, and sump pump sizing for foundation waterproofing systems.

Foundation Perimeter Length (ft) Foundation Wall Height / Depth (ft) Foundation Wall Thickness (in)

Drain Pipe Diameter (in) Pipe Slope (in/ft) Manning's n (pipe roughness)

Gravel Trench Width (ft) Gravel Trench Depth (ft) Membrane Overlap / Extra (%)

Design Rainfall Intensity (in/hr) Drainage Area (ft²) Runoff Coefficient (C)

1. Pipe Flow Capacity — Manning's Equation (full-flow circular pipe):

Q = (1/n) × A_pipe × R_h^2/3 × S^1/2

where A_pipe = π·d²/4, R_h = d/4 (hydraulic radius for full circular pipe), S = slope (ft/ft), n = Manning's roughness coefficient.

2. Gravel Backfill Volume:

V_net = (L × W_trench × D_trench) − (π·(d/2)² × L)

Convert ft³ ÷ 27 = yd³; weight ≈ yd³ × 1.4 tons (crushed stone).

3. Waterproofing Membrane Area:

A_membrane = (L × H + L × t_wall) × (1 + overlap%/100)

where H = wall height, t_wall = wall thickness (ft).

4. Sump Pump Sizing — Rational Method:

Q_runoff = C × i × A_acres [ft³/s]

Q_pump = Q_runoff × 1.25 (25% safety factor) → convert to gpm (× 448.831)

where C = runoff coefficient, i = rainfall intensity (in/hr), A = drainage area (acres).

Manning's equation assumes steady, uniform, full-pipe flow — actual capacity at partial flow may differ.
Gravel density assumed at ~1.4 tons/yd³ for clean crushed stone (ASTM D448 #57 or similar).
Membrane area includes the vertical wall face and the footing face; does not include horizontal footing top.
Rational Method (Q = CiA) is valid for drainage areas up to ~200 acres (ASCE, FHWA HEC-22).
Sump pump sizing includes a 25% safety factor per common industry practice (AIHA, NFPA 13).
Pipe slope minimum of 1/8 in/ft (1%) recommended by IRC Section R405 for foundation drains.
Manning's n values: PVC/HDPE smooth pipe ≈ 0.011; corrugated plastic ≈ 0.013 (ASCE MOP 36).
Runoff coefficients per ASCE/SEI 7 and local stormwater management guidelines.
Results are estimates for preliminary design; consult a licensed geotechnical or civil engineer for final design.

In the network