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Drainage Specialist terms explained — Welwyn Garden City glossary

Lateral Drain(Lateral)

The length of pipe carrying waste from your property boundary to the public sewer. Since the 2011 transfer this is normally maintained by the water company, so a blockage there is often attended free — worth one phone call before paying a contractor.

Build-Over Agreement(Build-over)

The water company’s written consent to build over or near a public sewer. Missing consent is one of the most common reasons a finished extension causes trouble at sale, long after the builder has gone.

CCTV Drain Survey(CCTV survey)

A camera run through the drain, coded to a recognised standard so the report reads the same to your insurer, your surveyor and the next contractor. Ask for the footage and the coded report, not a verbal verdict.

Patch Lining(Lining)

A resin sleeve cured in place to seal a cracked section without excavation — far cheaper than digging up a driveway. It requires a structurally sound host pipe, so a genuinely collapsed drain cannot be lined, whatever the quote says.