What is a Build Over Agreement?

a drain within the boundary of your extension will require a build over agreement
(Image credit: Paul Fears)

A Build Over Agreement (BOA) may be required when building an extension to your home. This is a legal agreement between you and your water company that guarantees that your work will not only not negatively affect a public sewer located underneath or near the boundary of your build, and that they will still have a way to access the sewer if and when repair and maintenance work is required. 

In this handy guide, discover how you know when you need one, how long they take and the costs involved, as well as design advice for building over a public sewer.

Ian Rock

Chartered surveyor Ian Rock MRICS is a director is Rightsurvey.co.uk and the author of eight popular Haynes House Manuals, including the Home Extension Manual, the Self Build Manual and Period Property Manual.

Ian is also the founder of Zennor Consultants. In addition to providing house surveys, Zennor Consultants provide professional guidance on property refurbishment and maintenance as well as advising on the design and construction of home extensions and loft conversions, including planning and Building Regulations compliance.

Ian has recently added a 100m2 extension to his home; he designed and project managed the build and completed much of the interior fit-out on a DIY basis.