New Build Drains Blocked Already | Why It Happens

I got a call from a couple in Monkspath last spring. They'd moved into their new build eight months earlier, thrilled with the place, fresh everything, not a scratch on it. Then their downstairs toilet started backing up. Then the kitchen sink. Then they noticed the manhole cover in the garden was sitting slightly proud of the ground, like something was pushing it from underneath.

They'd already been back to the developer twice. Told it was 'settling'. Told to pour hot water down. Told, basically, to go away.

They weren't imagining it. The drain was blocked. And the reason it was blocked had nothing to do with how they'd been using it.

What we found when we lifted the covers

I'll be honest: I half-expected something mundane. A fat plug, maybe a cotton bud or two. New builds attract new occupants, and new occupants sometimes haven't learned yet what a drain is not a bin for.

But this was different from the second I put the camera in.

The lateral drain running from the house to the adoptable sewer had a significant partial blockage about four metres from the first inspection chamber. On camera, it looked like a pile of gritty grey matter wedged into the invert. I pushed past it and found more: a stretch of pipe where the base was furred with what I can only describe as dried plaster slurry. Further along, sitting as bold as you like in the 100mm pipe, was a work glove. A builder's glove, the knitted cotton type, dark with age, completely blocking roughly two-thirds of the bore.

Beyond the glove, more debris. Small chunks of brick. Aggregate that had clearly been rinsed off tools or a mixer and had just settled and set in the low spots of the run.

This drain had been used as a site drain during construction. Then handed over as a finished product.

Why new build drains fail in year one

This isn't a one-off. I've seen versions of this in Dickens Heath, in Hillfield, in Marston Green, in the newer parts of Balsall Common. The mechanisms are almost always the same.

Construction debris left in the run. Drains are open during the build. Soil pipe connections get temporarily capped or they don't, inspection chambers sit open to the elements, and site workers, not maliciously, just practically, use the drainage system for what's convenient. Mixing water goes down. Plaster washings go down. Offcuts get dropped and lost. A glove falls in while somebody's kneeling over a chamber. Nobody retrieves it.

Mortar and plaster slurry. This is the one that causes the slow, insidious blockages. Liquid mortar and plaster wash into the drain and behave like water until they don't. They settle into the lower half of the pipe, cure slowly, and leave a rough, encrusted surface that catches everything that comes after it. Six months later, the first proper load of toilet paper hits that rough patch and you've got your blockage.

Poor pipe falls and misaligned joints. Sometimes the debris isn't the whole story. I've surveyed new build drains where a section of pipe had been laid with insufficient fall, meaning wastewater slowed and solids dropped out of suspension before they reached the sewer. Other times, a joint was slightly offset during backfilling, leaving an internal lip that snagged debris. These are workmanship issues, not occupant issues, and they're almost impossible to spot without a camera.

Temporary drainage connections never made permanent. Groundworkers sometimes install temporary connections to manage site runoff, and occasionally those temporary measures get buried in the final build rather than replaced. I've seen it.

Exactly what we did on the Monkspath job

First pass was a CCTV survey of the full lateral drain from the house to the sewer connection. We logged every defect with footage: the plaster slurry sections, the debris accumulations, the glove, and one section of pipe where the joint was slightly open, not critical, but not right.

We gave the homeowners a copy of the footage and a written report before we touched anything else. That matters, because they needed the evidence for the developer.

Then we jettted the whole run using high-pressure water jetting at appropriate pressure for 100mm plastic drainage. The plaster slurry took two passes, it had set firm in places. The glove came out in pieces. The aggregate flushed through. We retrieved what we could from the chamber and bagged it.

Second CCTV pass to confirm the pipe was clear and to document the defects we'd found. The misaligned joint and the borderline pipe fall both went into the report.

Total job time: about two and a half hours.

The homeowners then went back to the developer with footage of the glove, the slurry, and the joint defect. The developer's response changed considerably when there was camera evidence in front of them rather than a complaint they could wave away.

The before and after in plain numbers

What the snagging period actually means for your drains

Most new build homes come with a two-year developer warranty (NHBC Buildmark or equivalent) and a ten-year structural warranty. The snagging period, the window where you can formally ask the developer to fix defects, is typically the first two years.

Here's the problem. Drainage defects are largely invisible. You can walk every room with a snagging list and catch a draughty window seal, a misaligned kitchen door, a bit of paint over a switch plate. You won't catch a construction glove four metres down a drain.

By the time the blockage makes itself known, you might be into month eight or month fourteen. You've already mentally filed the house as sorted. And when you go back to the developer, they'll question whether the problem is your doing rather than theirs. Without camera evidence, that argument is very hard to win.

A CCTV drain survey done in the first few months, before you've had time to make any mess of the system yourself, is your insurance. If the drains are clean and well-laid, the survey gives you peace of mind and a baseline record. If they're not, you've found it while you still have leverage.

What to push your developer for before snagging closes

If you're in a new build and the snagging period is still open, here's what's worth raising:

• Request evidence that the drainage system was inspected and signed off before handover. A reputable developer will have this. Many won't.
• Ask specifically whether the lateral drain was camera-surveyed after construction and before the site was adopted. Not just pressure-tested, surveyed.
• If they can't provide a clean CCTV report, that's a gap in their due diligence, and it's reasonable to request one is carried out at their cost.
• Any blockages or slow drainage in year one should be reported in writing immediately, not just verbally. Email creates a record.
• If you commission your own survey and it finds construction debris, that report is your evidence for a warranty claim. Keep everything.

Developers know how snagging works. The homeowners who get results are the ones who show up with footage, not feelings.

The wider pattern I keep seeing

Monkspath isn't unique. I've been called to new build properties in Castle Bromwich where a full inspection chamber lid had been concreted in during landscaping, making it inaccessible. I've surveyed drains in the newer Dickens Heath developments where offcut plastic pipe had been dropped into the run during installation and just left. B37, B90, B93, the postcode doesn't seem to matter much.

Some developers are better than others. Some groundwork contractors are better than others. But the incentive to rush drainage before the slab goes down, and the lack of routine post-construction camera inspection on many domestic sites, means that what happened in Monkspath is not unusual.

I don't think most of it is deliberate. I think it's a combination of time pressure, a lack of accountability at handover, and the fact that drains are underground and nobody will know until they know.

You'll know when it backs up into your bathroom.

The lesson for anyone moving into a new build

Get the drains surveyed in the first three months. Before the snagging period gets old, before you've put anything through the system that anyone could question, and while the developer's warranty team still has a reason to take your calls.

It's not about distrust. It's about the fact that a camera is the only way to see what's actually in those pipes. And what's sometimes in there is a builder's glove and six months of cured plaster slurry.

If you're already past the snagging period and things are starting to slow down, get the survey done anyway. At minimum, you'll know what you're dealing with. At best, you'll have evidence that supports a warranty claim even after the standard window, particularly if the defect is structural rather than a simple blockage.

Drainsco covers Solihull and the B postcodes, and we carry out CCTV drain surveys as standalone jobs, no need to have a blockage first. Engineers are available 24/7, there's no call-out fee, and you'll get a clear price before we start. Give us a ring if you want to know what's actually in your new drain.