What This Solves
Calculates foundation drain pipe sizing and sump pump requirements for basement and crawlspace waterproofing based on groundwater inflow and soil permeability.
Best Used When
- You are designing a perimeter foundation drain system for a new building
- You need to calculate the groundwater inflow rate to size the drain pipe and sump pump
- You want to verify that an existing foundation drain system has adequate capacity
Do NOT Use When
- You need a yard or field drainage system rather than a building foundation drain — Use French Drain Calculator
- You need to size only the sump pump without foundation drain calculations — Use Sump Pump Calculator
Key Assumptions
- Groundwater inflow is estimated using Darcy's Law with the surrounding soil hydraulic conductivity
- The drain pipe is installed at or below the footing elevation
- Filter fabric or graded aggregate prevents soil migration into the drain
- The sump pump runs intermittently based on pit volume and inflow rate
- No significant artesian pressure or confined aquifer conditions
Input Quality Notes
Soil hydraulic conductivity is the most uncertain input. Use field percolation tests at footing depth if possible. Seasonal high groundwater elevation should be the design condition, not average.
Calculate Foundation Drain Design
For educational purposes only. Not a substitute for professional engineering judgment.
Foundation Drain Design Overview
Foundation drains (footer drains) collect and remove groundwater and surface water from around building foundations. They protect against hydrostatic pressure, basement flooding, and foundation damage.
- Groundwater Flow - Calculated using Darcy's Law with soil hydraulic conductivity
- Surface Water - Calculated using Rational Method (Q = CiA)
- Pipe Capacity - Determined using Manning's equation for pipe flow
- Sump Pump - Required when gravity outlet is not available
Soil Hydraulic Conductivity Values
| Soil Type | Min (ft/day) | Typical (ft/day) | Max (ft/day) |
|---|---|---|---|
| Gravel | 2800 | 14000 | 28000 |
| Sand | 28 | 140 | 560 |
| Sandy Loam | 2.8 | 14 | 56 |
| Silt Loam | 0.28 | 1.4 | 5.6 |
| Clay Loam | 0.028 | 0.28 | 1.4 |
| Clay | 0.00028 | 0.0028 | 0.028 |
Source: Mays, L.W. (2011), Water Resources Engineering, Table 3.4
Standard Sump Pump Sizes
Common residential and commercial sump pump capacities (GPM):
A 25% safety factor is applied when selecting pump size.
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Last verified: February 2026