Foundation Drain Calculator

Calculate foundation drain sizing for basement and crawlspace waterproofing. Determines pipe capacity, groundwater inflow, and sump pump requirements using HEC-22 methodology.

Calculate Foundation Drain Design

For educational purposes only. Not a substitute for professional engineering judgment.

Input Parameters

Foundation Properties

Foundation Type

Type of foundation structure

Perimeter Length

Total perimeter of the foundation

Foundation Depth

Depth of foundation below grade

Footing Width

Width of the foundation footing

Surface Water Contribution

Contributing Surface Area

Area draining surface water to the foundation drain

Design Rainfall Intensity

in/hr

Peak rainfall intensity for design storm

Soil & Groundwater

Soil Type

Surrounding soil type for groundwater infiltration

Groundwater Depth

Depth to groundwater table below grade (0 if at surface)

Drain Pipe Properties

Pipe Material

Material affects Manning's roughness coefficient

Pipe Diameter

Interior diameter of drain pipe

Pipe Slope

Slope of drain pipe (ft/ft or m/m)

Outlet Configuration

Outlet Type

How water is discharged from the drain system

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):

20 GPM33 GPM50 GPM75 GPM100 GPM150 GPM200 GPM

A 25% safety factor is applied when selecting pump size.