New Build Drainage Problems Salisbury | What to Check
New-build drainage defects are common on Harnham estates. Steve Marsh at Drainsco explains what goes wrong, who's responsible, and what to do about it.
I got a call last autumn from a couple who'd moved into a new-build on the edge of East Harnham. They'd been in the house eleven months. Every time it rained hard, the manhole at the side of the property backed up and dirty water crept across their patio. The developer had been out twice, declared everything fine, and stopped returning calls. The couple were two weeks away from their two-year NHBC warranty deadline.
We got there, ran a CCTV survey, and found building debris sitting in the lateral drain, a near-90-degree jetting bend that was installed the wrong way round, and a shared private sewer connection that nobody had told them existed. Three separate problems. None of them unusual. Not on new builds.
Why new-build drains aren't as clean as you'd expect
People assume a brand-new house means brand-new, fault-free drainage. It usually isn't. Sites are busy, ground workers are under pressure, and nobody is watching every pipe joint get bedded in. By the time the turf goes down and the fences go up, what's underneath is fixed and largely forgotten.
The most common things I pull out of new-build drains:
- Lumps of concrete from the groundworks, just sitting in the barrel of the pipe
- Off-cuts of plastic conduit or pipe lagging that slid in during the build
- Mortar droppings from brickwork that was cleaned down above a gully
- Grit and silt from incomplete backfill, washed in before the connections were capped
Any of those will slow a drain. One of them jammed against a joint in the wrong place will back up the whole run.
The shared private sewer problem
Harnham and the surrounding SP2 postcodes have seen a lot of infill development over the past fifteen years. When developers build out a small site, they often connect multiple plots to a single shared private sewer before it meets the main public system. That sewer is private. Water companies don't maintain it. The residents do, jointly, even if they've never been told.
I find homeowners genuinely shocked by this. They bought a new house. They assumed the drainage was sorted. Nobody mentioned that the pipe running under the shared driveway belongs to them and their three neighbours equally.
Check your property title documents. If you see a reference to a shared drain or a maintenance covenant, that's worth understanding before something blocks and everyone points at everyone else.
The developer sign-off gap
Developers sign off drainage to building control using a pressure test and a visual inspection at completion. That test tells you the pipes don't leak under static load. It doesn't tell you what's sitting inside them, and it doesn't tell you how the system performs under real rainfall loading over months of use.
By the time the first winter hits, debris that was dormant starts moving. Joints that passed inspection start to leak slightly as ground settles. A CCTV survey done at the eleven-month mark, before your NHBC warranty expires, is the most useful thing you can spend money on as a new-build buyer. It gives you evidence. Evidence the developer has to respond to.
What a pre-expiry CCTV survey actually shows
| Defect type | How it shows up on CCTV | Typical remedy |
|---|---|---|
| Build debris in pipe | Visible obstruction, often partial | High-pressure water jetting to clear |
| Misaligned joint | Step or gap in pipe wall, possible root entry point | Drain repair or relining |
| Pipe laid to wrong fall | Pooling water visible in camera footage | Excavation and relay or patch liner |
| Incorrect fitting installed | Camera can't pass, or shows wrong flow direction | Excavation and replacement |
| Collapsed section | Obvious deformation or full blockage | Excavation and relay |
A survey report with footage is something you can hand to a developer or NHBC and say: fix this. Without it, you're just having a conversation.
What to do if you're in this position
If you're on a newer Salisbury estate, whether that's East Harnham, Netherhampton Road, Bishopdown, or any of the other sites that have gone up around SP1 and SP2 over the last decade, and you've had any drainage sluggishness, smells, or slow gullies, don't wait for a full blockage. Get a CCTV survey done.
If you're inside your NHBC warranty window, the footage gives you a formal snagging record. If you're outside it, you at least know exactly what you're dealing with and can make an informed decision about repair. On remedial work, drain repairs and relining, Drainsco backs the work with a 20-year guarantee.
Drainsco covers Salisbury and the SP postcodes, with engineers available 24/7. No call-out fee. You'll get a clear price on the phone before we start. If you've got a new-build drainage concern, give us a call and we'll tell you straight what we think you need.
Steve Marsh, Lead drainage engineer
Steve has been clearing drains in and around Salisbury for over two decades. He has rodded, jetted and dug up most of the pipework in the SP postcodes, and he has strong opinions about what really blocks a drain and what people only think blocks it.
Blocked drain in Salisbury?
Engineers on call 24/7. A clear price before we lift a cover, and no call-out fee.
01722 449093