Yes, there are scenarios in which you may be able to build an extension over a drain, but it is by no means straightforward or easy. 

Whether you’re a homeowner looking to increase your usable living space or a contractor who has been asked to scope out a potential property extension, there are many factors to consider – and drains are often a tricky aspect of this.

This month at Express Drainage Surveys, we’re going to guide you through everything you need to know about the topic so that you can make an informed decision. Remember, if you need professional mapping of your drainage system to assist you with planning your extension, look no further than our expert team.

Understanding the drains under your property

Knowing what type of drain is under the area you’re planning to build over is vital. If the drains in question serve just your property and no others, it’s your private drain and your responsibility, while multiple properties share public sewers so any changes could impact more than just your home.

If you’re building over a private drain, things should be much easier than over public sewers, but you’ll still need to carefully plan and ensure you’re acting in line with building regulations.

We’ve covered the topic of shared drains and how to find out who is responsible for what in our previous post, which you can read here.

What if there’s a manhole cover in the way?

You should never build an extension over a manhole cover or inspection chamber.

Ultimately, if there is a manhole providing access for drain maintenance and repairs, covering it or removing it without permission can lead to some serious legal repercussions and potential structural issues. You’ll need an agreement if you want to move the manhole, but this could be extra effort on top of planning an extension.

Can you legally build over a drain cover?

Making sure you don’t fall afoul of the law can ensure you don’t make any costly mistakes. The last thing you want to do is spend thousands on a new extension, only to find that it has to be removed or destroyed because you’ve not adhered to regulations in relation to drain covers.

• UK building regulations. If you plan to build within three metres of a public sewer or one metre of a public lateral drain, you’ll need to get in touch with your local water authority. This is according to Building Regulation H4 and is in place to ensure you don’t adversely affect the sewer system for other properties.
  
• Do you need a build-over agreement? If you do plan to build over or near public sewers, to do so legally you’ll require a build-over agreement with the local water authority. This helps to ensure construction is carried out to the right standard during and after. You won’t need this agreement if it’s a private drain.

Legal fines and even issues selling your property can arise if you fail to adhere to the law on this matter, so it really does pay to do your research and work with professionals.

Technical challenges of building over a drain

As well as the challenges relating to understanding your drain type, the local water authority and the regulations you have to adhere to, there are also technical challenges.

The first set of considerations you’ll have are structural ones. Firstly, you will want to ensure that the foundations of your extension don’t damage the underground pipes. This is something a professional builder should be able to cover with you to discuss reinforced lintels or alternative foundation solutions.

Next, the practicalities of drain access and maintenance need to be accounted for. Keep in mind that future access should be planned for if building over a drainage system. This could involve rerouting drains – which can be costly – or including removable panels in your extension.

Root intrusion and blockages could already exist within your drainage system, something you will need to address before making any plans for an extension. A pre-build drain survey is a great idea to help you map out the drainage system, while CCTV cameras can establish the condition of your system before you get ahead of yourself.

What are the alternative options?

So, what other options are there if you have a manhole or drain cover in the area you wish to build an extension on? There are a few things to consider, though a lot will depend on your specific property and the plans you have in mind.

• You could move the drain cover if relocation is feasible and the local water authority gives you the approval (never do this without permission).
• Another option is to build around the drain cover, ensuring it’s left accessible by placing your extension away from it. This keeps it in place but may still require permission depending on what type of drain system it is – always seek professional guidance before making any plans.
• The third option available is to reroute the drainage system altogether, but depending on the lay of the land, this could be a mammoth undertaking, so requires very careful consideration before making any changes.

How we can help with professional drain surveys

As you can probably tell, there are a lot of different factors to this topic, which is why we’re here to support you with CCTV drain surveys. We offer pre-build surveys that can identify any potential issues in your drains before you begin construction, helping you and your builders to avoid any costly mistakes.

We also offer specific build-over drain surveys to help you uncover hidden drains and awkward layouts. This is crucial to gaining build over permission from local water authorities as it provides drain mapping to professional standards thanks to our knowledge and expertise.

Looking for domestic CCTV drain surveys or commercial CCTV drain surveys in your area?

Look no further than Express Drainage Surveys – our dedicated team are on hand to assist you whether you need to plan for an extension to your property or you have drainage issues and need to get to the bottom of them.