The Most Common Drainage Mistakes We Find After Building Work

Most people understandably assume that once building work is finished, everything underground has been done properly too.

But over the last few years, we’ve attended more and more blocked drain jobs across Haywards Heath, Burgess Hill and Mid Sussex where the real problem was not old drains or bad weather, but mistakes made during previous renovation or extension work.

Usually the customer calls because something simple has started happening. A kitchen sink becomes slow, an outside gully begins overflowing when it rains, or a toilet suddenly starts struggling more than it used to.

At first it sounds like a straightforward blocked drain.

Then we investigate further.

When Building Work Causes Drainage Problems

One thing we’re seeing more often is drainage systems being altered during:

• Kitchen renovations
• Extensions
• Patio and landscaping work
• Utility room installations
• Garage conversions

Most of the time the work above ground looks great. Fresh kitchens, new paving and neatly finished extensions.

But underground can be a different story entirely.

Because drainage is hidden away, problems often go unnoticed until months or even years later when the system starts struggling.

Incorrect Connections Are A Big Problem

One of the most common issues we now find is kitchen waste connected into rainwater drainage.

This usually happens because the nearest available drain or gully was used during the work.

At first, everything may appear to function normally. But over time, fats, grease and food waste begin building up inside systems that were only ever designed to carry rainwater.

Eventually the soakaway or surface water system starts failing.

That can lead to:

• Repeated blocked drains
• Overflowing gullies
• Standing water
• Bad smells
• Slow sinks during wet weather

This year’s prolonged rain across Mid Sussex has exposed a lot of these hidden issues.

Poor Pipe Falls And Incorrect Fittings

Drainage relies entirely on gravity, so the way pipework is connected underground matters far more than many people realise.

We regularly uncover pipework installed with poor fall, uneven flow, or fittings being used in ways they were never really intended for.

The image below is a good example. The fittings being used here are designed primarily for vertical stack pipework, where waste naturally drops downward with gravity. In a vertical stack, waste from separate connections can pass each other without causing too many issues because everything is flowing downward.

The problem comes when these same fittings are used horizontally beneath floors.

Instead of waste flowing away independently, flow from one side of the system can travel directly across into the opposing connection. Over time this can cause turbulence, poor flow and waste collecting where the pipework interacts, eventually leading to recurring blockages.

The correct method would usually involve staggering the connections so the flow paths do not directly oppose each other within the horizontal run.

At first, systems like this may appear to work reasonably well, which is why problems are often missed initially. Then gradually sinks begin draining slower, toilets become less reliable and recurring blocked drains start appearing later on.

Buried Chambers And Hidden Access Points

We also regularly find inspection chambers that have disappeared beneath:

• Patios
• Artificial grass
• Driveways
• Decking

Sometimes homeowners do not even realise drainage access points have been covered over during landscaping work.

This becomes a major problem later when:

• drains need clearing
• inspections are required
• blockages occur underground

Without proper access, even simple drainage work becomes more difficult and expensive.

What To Look Out For After Renovation Work

If you have recently had building work carried out, there are a few warning signs worth paying attention to.

Common signs something may not be right:

• Slow kitchen sinks
• Toilets struggling to flush
• Gurgling drains
• Bad smells outside
• Gullies overflowing during rain
• Repeat blockages in the same area

Often these problems appear gradually rather than all at once.

Questions Worth Asking Your Builder

You do not need to become a drainage expert, but asking a few sensible questions early can prevent major problems later.

It is always worth asking:

• Where is the new waste pipe connecting?
• Is this foul drainage or surface water drainage?
• Will the existing drains cope with the added load?
• Have the drains been tested before being covered over?
• Will inspection chambers remain accessible?

Most reputable builders will have no problem answering these clearly.

Why CCTV Inspections Matter

Because drainage systems are hidden underground, many problems simply cannot be diagnosed properly from the surface.

A CCTV drain inspection allows us to:

• See how the system is connected
• Identify poor installation work
• Locate restrictions and damage
• Assess flow through the system
• Confirm whether drains are functioning correctly

In many cases, this prevents homeowners repeatedly paying to clear the same blockage without addressing the real cause.

Not every blocked drain is simply bad luck or normal wear and tear.

Increasingly, we are finding recurring drainage problems linked to shortcuts, poor planning or mistakes made during previous building work.

Most of these issues are preventable when drainage is considered properly from the beginning.

If your drains have never seemed quite right since renovation work was carried out, there is usually a reason.

Frequently Asked Questions

Why does my drain keep blocking after being cleared?

If a drain keeps blocking, there is usually an underlying issue such as a collapsed pipe, root intrusion or a structural defect. Clearing the blockage only removes the symptom, not the cause.

What is a collapsed drain pipe?

A collapsed drain pipe is where part of the pipe has broken or lost its shape. This can restrict flow and allow soil or debris to enter the system, leading to repeated blockages.

Can a blocked drain be a sign of pipe damage?

Yes. While some blockages are caused by build-up, repeated or persistent issues often indicate damage such as cracks, offsets or collapsed sections.

How do you find a collapsed drain?

The most effective way is with a CCTV drain inspection. A camera is inserted into the pipe to identify damage, blockages and the overall condition of the system.

Can a collapsed drain be repaired without digging?

In some cases, repairs like lining can be used. However, if the pipe has fully collapsed or is severely damaged, excavation and replacement may be required.

What are the signs of a damaged drain pipe?

Common signs include repeated blockages, slow drainage returning quickly, bad smells, gurgling noises, or problems worsening during heavy rain.