Drainage when extending a house

This is general information, not a survey, design, legal or Building Control decision. The correct scope and standard depend on the property, work, date and regulatory route.

Locate drains, manholes and inspection points before finalising an extension. Flow direction, invert levels, falls, access for maintenance and protection from foundations all need checking.

A public sewer near or beneath proposed work may involve a water authority build-over process. Never cover or divert drainage based on a drawing assumption alone; survey and confirm the responsible authority's requirements.