Connecting New Drainage to Existing Drainage Systems

When connecting new drainage to existing drainage systems, you need some careful planning, regulatory compliance and professional assessment to make sure you get a safe, efficient flow for wastewater.

Here in the UK, your new drain connection will need to comply with Building Regulations Part H, and may need approval from the local water authority in some cases. The process itself will involve surveying your existing system and identifying the pipe size and connection, as getting it wrong could lead to blockages, backflow and structural damage – not to mention the potential for legal costs if it impacts others.

For homeowners, developers and contractors, a professional CCTV drainage survey is often the first and most important step. Which is why, as drainage inspection professionals, the Express Drainage Surveys team is providing more guidance on connecting to existing drainage in the UK.

Why proper drainage connections matter

Here’s why it matters: your drainage system was designed to carry wastewater safely away from your property into the public sewer network and on to a treatment system. When you start an extension, outbuilding, kitchen relocation or any new build, it means you have to carefully integrate the new drainage to the existing one to avoid:

Frequent blockages due to poor flow dynamics
Sewage surcharging or internal flooding
Foul odours entering your property
Damp and structural deterioration
Environmental contamination

As you might expect, there are also legal implications if you don’t ensure your drainage connection complies with the building regulations and local authority requirements. Defective or unlawful connections can mean delayed property sale, invalidated warranties and can result in enforcement actions.

Understanding the existing drainage system

Before you make any connection, you have to fully understand what you are connecting the new pipework into. This is where it pays to understand the difference between a private drain, a lateral drain and a public sewer – a topic we’ve covered in a previous post if you want to brush up on the details.

The key thing to know is that if you intend to connect new drainage to existing public sewer drains, you will likely need formal approval. For that, you need to identify what type of drain and pipe you’re connecting to, which leads us to the next point.

You should also consider your neighbours and planning permission requirements for any project that you’re undertaking where new drainage connections are needed. You may need the consent of your neighbour to have the work done, so early, honest communication is important to avoid disappointment and disputes.

Why a CCTV drainage survey is essential

CCTV drainage surveys help you get a clear internal view of the pipework and this allows specialists to assess:

Pipe material
Internal diameter
Direction and depth of flow
Structural integrity
Existing defects or previous repairs

It can also highlight a range of issues with the drainage system you’re connecting to, making it worth your time so that you avoid any costly delays and re-excavation work later.

Should you end up connecting new pipework into a defective or partially collapsed drain, you could accelerate the failure of the system overall, creating much more serious long-term problems.

Methods of connecting new drainage to existing systems

There is no one-size-fits-all approach to connecting new drainage to existing drainage. It all depends on the pipe condition, depth, material and accessibility. Here are four common ways you may come across:

Connecting to an existing inspection chamber: This, of the four approaches listed, is probably the simplest and safest method. It involves breaking out part of the chamber wall, installing a new channel connection and re-benching to ensure you get a smooth flow. – That said, extra care should be taken to maintain the correct flow and avoid creating turbulence.
Cutting into an existing pipe run: If there isn’t a suitable chamber, it might be that you need to cut into existing pipework to add a new junction. This involves installing a Y-junction, using slip couplers and installing saddle connections where applicable. – If you have pitch fibre or clay pipes, there is a risk that they might crack during the cutting, so additional care must be taken to preserve structural integrity.
Installing a new inspection chamber: For some connections, a new inspection chamber may have to be installed at the connection point. This may end up being the most practical solution to provide future maintenance access, safest integration and compliance with access requirements.
Connecting to a main sewer: In instances where you’re connecting directly to a public sewer, there may be specialist methods required. Typically, the work will need to be overseen by the local water authority, with approval for any connection saddles you intend to add.

Getting correct falls and alignment

Because drainage relies on gravity, you need to have the correct fall within the system. Without this, the waste will not flow efficiently. The typical gradient is between 1:40 and 1:80 on 110mm foul drainage pipes.

If the fall is too steep, the liquids will outrun solids and cause blockages, while if it’s too shallow, there will be insufficient flow speed, leading to a buildup. Any professional installers will use laser levels and accurate setting-out methods for compliance, with a tendency to avoid bends wherever possible.

How to choose the right pipework and fittings for connections

Most modern domestic drainage in the UK will use 110mm uPVC pipes. However, if you have an older system, it could be clay, concrete or pitch fibre pipes. When choosing your materials, here are a few key tips:

Match your pipe diameter precisely for a snug fit
Use the appropriate couplings for any differing materials
Make sure your fittings meet the relevant British Standards
Avoid using incompatible jointing systems

CCTV drain surveys for new drainage connections

At Express Drainage Surveys, we’re always on hand to assist you in getting new drainage connections done right. That means you’ll be able to proceed with confidence thanks to the use of our specialist drainage camera technology and detailed reports.

As part of our commitment to helping you with every aspect of your drainage, the following are just some of the services we provide:

Arrange a CCTV inspection for your drains as part of any new additions and get peace of mind thanks to our expert technicians.