Check bounded Approved Document H minimum falls using actual internal pipe size, design flow, connected WCs and run length.
How to use the Drainage Fall Checker
Choose foul or surface water; combined and pumped systems are intentionally outside the checker.
Enter the actual internal pipe diameter, straight run length and planned invert drop.
For foul water, use an exact dwelling-flow lookup or enter the calculated peak flow and connected WC count.
Review the exact table minimum and the installation checks that still need competent project verification.
Why use this tool
Uses exact bounded rows from Approved Document H rather than invented typical falls.
Checks flow, internal size and WC conditions before returning a foul-drain result.
Stops unsupported combinations instead of interpolating or presenting a false pass.
This is a minimum-fall and bounded table checker, not a complete drainage design. Capacity, access, ventilation, route, changes of gradient, bedding, cover, invert levels, connection, approvals and surface-water destination still need project checks. Surface-water results do not prove hydraulic capacity for the catchment and rainfall.
Part of Builder Tools Calculators — construction tools for UK tradespeople.