Drainage is the single most common cause of delay and rework on a groundworks package. Unknown pipes get struck by excavators, extensions land on live sewers, and building control refuses to sign off layouts that cannot be evidenced.
The good news is that most properties already have some form of drainage record. A.R.C Build Ltd works from these plans every week, so this is the order we would search in.
Five ways to get a drainage plan
Start with your water and sewerage company
Most public foul and surface water sewers are owned by the regional water company. Every one of them holds a sewer records map (often called an asset location search or sewer map) that shows public sewers, manholes, pipe sizes and flow directions near your property. You can request it online, usually for a small fee, and receive a plan within a few working days.
Ask the local authority for building control records
Private drainage inside your boundary is not on the water company map. Your local authority building control department may hold approved drainage layouts submitted with past building regulation applications, extensions or new builds. Planning portals also carry drainage strategies for larger schemes, which are free to download.
Check the deeds, searches and previous surveys
Conveyancing packs frequently contain a drainage and water search (CON29DW) with a sewer plan attached. Older deeds, homebuyer reports, and any CCTV drain survey carried out at purchase are all worth digging out before you pay for anything new.
Walk the site and lift the covers
Paper records are often incomplete. Lifting inspection chamber covers, noting rodding points, gullies, soakaways and where downpipes disappear tells you a great deal. Sketch what you find on a site plan with approximate depths and directions of flow — it is the beginning of a usable drainage plan.
Commission a drain mapping survey when records fall short
If pipes are unrecorded, shared, or you are building over or near a drain, a professional drain mapping or CCTV survey is the reliable answer. A camera and sonde trace the route, depth and condition of every run and produce a measured, scaled drainage plan you can hand to your engineer, building control or insurer.
How to read a drainage plan
- Solid lines normally show foul sewers, dashed or coloured lines show surface water. Check the key on every plan — conventions vary by provider.
- Circles mark manholes and inspection chambers, usually labelled with cover and invert levels.
- Arrows indicate direction of flow, which tells you where a connection ultimately discharges.
- Figures beside a run give pipe diameter and depth. These decide whether you need a build over agreement.
When to commission a survey
- Records disagreeThe sewer map and what you find on site do not match, or chambers appear that are on no plan at all.
- Building over a drainYou need accurate depths and positions to agree a build over or diversion with the water company.
- Recurring problemsSmells, slow drainage or standing water usually mean a defect only a CCTV survey will find.
Drainage plan FAQs
Are drainage plans for my house free?
Local authority planning records and any drainage search already in your conveyancing pack are usually free to view. A water company sewer map or asset location search typically carries a small administration fee, and a physical drain mapping survey is a paid professional service.
Who owns the drains at my property?
As a rule, pipework inside your boundary that serves only your property is private and your responsibility. Shared drains and sewers outside the boundary were largely transferred to the regional water company in 2011. The sewer records map shows which is which.
Do I need a drainage plan for a building project?
Yes, for almost any extension, new build or hard landscaping scheme. Building control needs to see how foul and surface water will be handled, and you must not build over or within three metres of a public sewer without a build over agreement.
What is a drain mapping survey?
A drain mapping survey uses a CCTV camera and a sonde locator to trace pipe runs underground. The result is a scaled plan showing pipe routes, depths, diameters, connections and defects — far more accurate than historic paper records.
How long does it take to get drainage records?
Water company sewer maps usually arrive within three to ten working days. Local authority record searches vary. A drain mapping survey on a typical residential plot is completed in a single day, with the plan issued shortly after.
Once you know where the drains are, the next question is what happens on site. Read our guide to what groundworks involve.