Build over and build near agreements
If any part of your extension, basement or new building sits over or within 3 metres of a public sewer, you need the water company’s written agreement before you build. We prepare the drawings and manage the application.
Why it matters
Since 2011 most shared drains and sewers serving more than one property are public and belong to the water company, even where they run under private gardens. Building over or close to one without an agreement can stop a sale, invalidate your building control completion certificate and leave you liable if the sewer is damaged or needs access. Building control bodies will not sign off foundations near a public sewer without evidence of the water company’s consent.
What is involved
1. Locate the sewer
We obtain the water company’s sewer records, and where needed a CCTV survey, to establish the line, depth and size of the sewer relative to your proposed foundations.
2. Design around it
Foundations are designed to keep load off the pipe – typically by taking the foundation below the invert level, bridging with a lintel or reinforced beam, or repositioning manholes outside the building.
3. Apply and agree
We prepare the site plan, foundation sections and application form and submit to whichever company owns the sewer – Thames Water, Severn Trent, Anglian Water, United Utilities, Yorkshire Water, Southern Water, Wessex Water, Welsh Water (Dŵr Cymru) or another sewerage undertaker in England and Wales, dealing with their queries through to a signed agreement.
Self-certified or formal agreement?
Where the sewer is small (usually 160 mm or less), shallow and the foundation design meets the water company’s standard criteria, many companies allow a quicker self-certified route with no fee. Larger, deeper or strategic sewers, basements and piled foundations need a full application with a fee and a longer review. We tell you which applies at the outset.
Frequently asked questions
How do I know if there is a public sewer near my house?
Your water company can supply a sewer map for your address and we obtain this as part of the service. Shared drains between neighbouring houses are almost always public.
Does this replace Building Regulations approval?
No. The build over agreement is a separate consent from the water company. Building control will expect to see it as part of the foundation inspection.
How long does it take?
Self-certified applications are usually acknowledged within days. Formal applications typically take several weeks depending on the company and whether a CCTV survey is required.
Building near a sewer?
Send us your proposed plans and the address and we will confirm what agreement you need.