The short answer
The drainage element of groundworks is priced by the run and the connection, not by a single rate. Land drains typically run around £35–£50 per linear metre, while a sump pump for a wet or low-lying site is commonly around £1,200–£2,000 installed. On a single-storey extension, a basic drainage allowance to connect into the existing system is often roughly £400–£900. The figure moves with how far the new run is from the existing drainage, how deep it has to go, the ground it passes through and whether new gullies, inspection chambers or a connection to the main sewer are needed.
Drainage is the part of groundworks that ties the build into the existing system. It is priced by length of run, depth and the connections required, so the variables below decide the figure more than any headline rate.
Typical UK figures
- Land drains~£35–£50 / linear metre
- Sump pump (installed)~£1,200–£2,000
- Extension drainage allowance~£400–£900
- Main driverlength & depth of run
- Adds costnew chambers / sewer connection
What drainage groundworks covers
- Foul drainage: connecting toilets, sinks and waste into the existing foul system or sewer, with gullies and inspection chambers as needed.
- Surface water: taking rainwater from roofs and hard surfaces to soakaways or the surface-water drain.
- Land drains: perforated pipe in gravel to take groundwater away from a wet site, typically around £35–£50 per metre.
- Pumped drainage: a sump and pump where the site sits below the drain level or the water table is high, commonly £1,200–£2,000 installed.
| Item | Typical figure | Notes |
|---|---|---|
| Land drains | ~£35–£50 / linear metre | perforated pipe in gravel |
| Sump pump (installed) | ~£1,200–£2,000 | for low-lying / wet sites |
| Extension drainage allowance | ~£400–£900 | basic connection into existing |
| New chamber / sewer connection | added cost | depth & approvals dependent |
Indicative UK figures for guidance. Sources: trade groundworks and extension cost guides.
Why connections and depth move the cost
The biggest drainage variables are how far the new run is from the existing system and how deep it has to be laid to keep the right fall. A short connection into a nearby chamber is modest; a long run across the site, a deep dig through difficult ground, or a new connection to the public sewer all add cost and may need approval. Wet or low-lying ground can also turn a gravity drain into a pumped one. As with the rest of groundworks, the accurate figure follows a look at the levels and the ground.
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Frequently asked questions
How much do land drains cost per metre?
Land drains — perforated pipe laid in gravel to take groundwater away — typically cost around £35–£50 per linear metre. A sump pump for a wet or low-lying site is commonly around £1,200–£2,000 installed.
How much is drainage on an extension?
A basic drainage allowance to connect a single-storey extension into the existing system is often roughly £400–£900, though a long run, a deep dig or a new sewer connection adds to that.
What moves the cost of drainage groundworks?
The length of the run, how deep it must be laid, the ground it passes through, and whether new chambers, soakaways or a connection to the public sewer are needed. Approvals from the water authority and building control can apply.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific site. They are guidance, not a quotation.