How to bridge over a sewer pipe

Planning a new building development? When you’re thinking of building an extension, or a new construction project, you must make sure there is nothing underneath the ground that may be affected. This can include gas pipes, water pipes and sewers, all of which form a vital part of the underground infrastructure that serves our homes.

It’s important to know how to bridge over a sewer pipe if it turns out that your project requires it. Read on to find out how to bridge over a sewer pipe from the experts at Lanes Group, including how to make sure no damage is caused to your home or drainage system, nor to the public sewer system.

What do I need to look out for?

You need to establish what drainage pipework exists within your property boundary and underneath the ground. Sewer pipes carry wastewater from two or more homes and are usually within your property boundary. Lateral drains carry wastewater from a single home, and meet the public sewer network outside that house’s boundary – you can read here to find out who is responsible for your drains. If you are unsure of the location of the drains beneath your home, a CCTV drain survey is often the best way to find them, which can enable you to plan your project such that the existing infrastructure is undisturbed.

Can I bridge over a sewer pipe?

There may be instances where existing pipes clash with the positioning of a proposed foundation and it would not be possible to build around them. One example of this may be a sewer pipe that runs from the back of a property and crosses over the intended line of the new extension’s concrete foundation. You must never build foundations along the length of a pipe, and if you intend to build parallel to the direction of a pipe the foundations must lie on one side or the other.

If you are building foundations at an angle to the sewer pipe, you can put concrete on either side of the pipe and bridge over it. This is one of the most common ways of bridging over a sewer pipe.

What happens if I build over a drain?

If you build over an existing sewer or drain, this can cause damage to the pipes. This could result in the pipes leaking or becoming blocked, which can potentially lead to health problems, odour nuisances and environmental damage. It also makes it harder, costlier and more time-consuming to replace and repair faulty drains, as well as to clear blockages. 

You should also avoid undertaking any building work that makes it harder for the water authority to access and maintain sewer pipes. There are regulations that govern how near to sewers and drains you can build, and you should consult these carefully before planning any building works.

Can I put foundations over drains?

It must be noted that the building regulations state that in some soils, such as silt or sands, buildings must not be constructed within or over 3m of a drain unless you have special measures in place. In some cases, you may need a 5m easement, if the pipe is more than 30cm in diameter. Extensions and buildings must not be constructed over an inspection point on a sewer or manhole.

The good news is that, in some cases, you can reroute and move drains if they are in the way of your building work. Drains are a component of complex networks of sewers, pipework and manhole covers. This means it is not always a case of simply moving just one drain. Instead, you may need to look into rebuilding the drainage system in a different location. You need to ensure it is at the right depth and you must obtain permission from your local water authority before getting started. In some cases, for these reasons, it may be unfeasible to do. Working with expert drainage surveyors like those at Lanes can help you to find the best solution for your requirements.

Build Over Agreements

Water authorities require a Build Over Agreement for any building work over public sewers, or if the work is within 3m of a sewer or drain pipe. This responsibility may even be found in your house deeds, especially if you have a modern property. It is essential that you obtain permission before undergoing any work.

Are there instances where I cannot build over a sewer?

Yes. There are certain situations where you will not be able to build over a sewer:

• Connecting a new property to a sewer may need approval and sometimes even works carried out by the water authority.
• Driven piles are not allowed within 15 metres of a public sewer. After this kind of sewer has been established, a lot of the processes and coordination can be relieved by contractors, structural engineers and architects.
• New detached developments are unlikely to have a Build Over Agreement granted. Instead, the sewer needs to be diverted. However, you will need to pay to undertake this work yourself.
• You cannot build over a manhole and must relocate it if you intend to build in the area of this or other access points. Manholes cannot be inside a building because of the heightened risk of smells or flooding, and so the only solution is to move the manhole to a suitable location.

If you have been dreaming about improving your property by extending it, you may find a manhole where the foundation of your new structure will go. Should you notice pipework present, you must get this approved by your water authority first.

Find out more

For support and advice on any drainage matters pertaining to a construction project, get in touch with Lanes today. You can read more about our sewer services and drain surveys, or give us a call on 0800 526 488.