Cost of Moving Drains For Extension

Last updated 3rd April, 2024

Do you need to move a main drain? Want to know the cost?

All you need to know about building over drains, creating a drain extension and removing a house drain. We've complied this article with all the associated costs including the supply costs, labour fees and more!

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The Cost Of Removing Drains For An Extension

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How Much to Remove Drains?

When adding an extension altering the drainage is often inevitable and the proper planning and execution of drainage modifications is vitally important.

Obviously, if your planned extension will be on top of a manhole cover, then you will have to make arrangements so that the drains can still be easily accessed even after the extension is complete, this will normally entail moving the drain or at least creating a new access which is acceptable to the local water authority.

What are the first steps?

Making a plan of how you intend to change the drainage system can help to avoid some of the many pitfalls with underground drainage. Creating a plan of the underground drains can be done in one of three ways.

First, check with the council to see if they have any plans of the house to use as a reference as this will be cheaper than getting a surveyor to do a plan of the drains beneath your home from scratch. You need to be careful when using old plans as things could have been changed with the drainage since those plans were created due to other building alterations.

Do I need a surveyor?

Hiring a surveyor will be costly but should give you correct and current information on your drainage system. The cheaper but more time-consuming option is to start lifting manhole covers and try to work out the layout of the drainage system and draw a plan yourself. Unless you are pretty confident and have some skills in this area, you would be best to use one of the other options.

What types of drainage are there?

Making changes to underground drainage is not an easy task. There are two types of underground drainage, surface water drainage and foul water drainage.

Surface water drainage includes gutters, pipes and drains that carry rainwater into the nearest canal or river, whereas foul water drainage takes the water from your sinks, washing machine, bath, shower, and toilet to the nearest sewer.

These two systems are always kept completely separate though it can be acceptable to let the surface water run into a foul water drainage system, but never the other way round! Nowadays there is also grey water, a third category.

Greywater systems keep the used water from baths, sinks and appliances separate from toilet waste and collect it in tanks where it can be filtered and pumped to storage tanks for use in the home where clean water isn't strictly required (such as watering the garden or for flushing toilets).

Grey water systems reduce the consumption of expensive drinking water for tasks that don't really need it while also reducing the amount of water that drainage systems have to cope with so reducing flood risk too. However, these grey water systems are still quite rare in the UK.

Do I need building regulations?

If you have to move a drain then it needs to be planned out thoroughly and whether or not you need permission depends on the individual project, but you should seek professional advice in every case as mistakes with permissions can be very costly to put right.

You need to refer to Part H of schedule 1 of the Building Regulations if you plan on doing the works yourself but it is likely that a building inspector will need to visit and carry out an inspection to ensure that everything meets the current regulations.

Anything else I need to consider?

Modifying gutters and drainpipes are pretty simple, just try to find the same make of drainage system to the one currently being used so it is easier to link the new pieces to the existing pieces, plus it will also look better than using a completely different type of drainage system.

However, modifying underground drains is much more difficult and expensive. Though it may seem like a complicated job, do not ignore obvious rules, make sure that all drains run downhill at a slight angle which is continuous to avoid overflowing drains and nasty smells or blockages.

The other main rule with drains that is sometimes overlooked, is that it is essential that all drainage systems can be unblocked by locating inspection chambers at junctions and bends in the drainage system. These inspection channels also allow air into the system which is needed to replace the water as it drains.

If you need new major junctions and inspection chambers, then it is essential that you get expert assistance.

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Removing Drains Prices

Initial costs for drain removal is for correct surveying of the drains - a basic scan being approximately £250. The work itself may take a few days to be completely finished, but if it is a smaller change, can be completed within a day. Conversely, for larger changes, this may take longer.

The work may require different materials depending on how much change is required for the drains involved. The length of the pipes required is central to the material cost, which depends on the type and quality of piping - a basic pipe can be as little as £5 for 1 metre, while a high quality or specific type of piping could be closer to £30 in some cases. Typically, piping willl be at the lower end of this price range.

Usually, the changes cost around £1000, but for additional complexity, may cost more.

Often the cost of labour will be around £250 per day, while the work can take between 1-3 days, depending on the varying difficulty, so the cost may vary by roughly £500.

Below are some estimated costs of drain removal required for an extension.

Job Description Avg. Cost Duration
Basic CCTV scan of your drains £250 1-3 Hours
New sewer line signed off by a building inspector £125 1-2 Hours
Move small drain for a kitchen extension £1000 1-3 Days

Cost Breakdown

Individual costs of a small drain removal for an extension - Total Cost: £1000






Waste Removal


If you make a Building Regulations application then Building Control will consult the Water authority in your area regarding the works. We recommend that you contact the local Water authority before making the application so that you can discuss and agree what works will be acceptable. Please note that planning consent does not grant approval to build within 3 metres of a public sewer.
Yes - you need to apply for a sewer diversion under Section 185 of the Water Industry Act 1991 and will be required to enter into a legal agreement with the local water company before any diversionary work commences.
This can get a bit complicated, but in general, a drain serves a single property whereas a sewer serves more than one property. Private sewers belong to the properties they serve. Public sewers are owned by the local water company so any building work on and around a sewer needs permission from the sewer owner. Most sewers are publicly owned and are maintained by your water company but there are some private sewers.
Building over an existing drain or sewer can damage the pipes and cause leaks or blockages which can lead to odour nuisance, health problems and environmental damage. It can also make it more difficult and expensive to clear blockages and make repairs to faulty drains. So if there is an existing drain below your proposed extension, it may need to be moved or reinforced which will increase the cost of your project.
Maps of public sewers can be inspected at the local authority or via the local water company, but private sewers and drains are not normally included on these maps. You are strongly advised to seek advice from a professional or your local authority building control department before committing to or commencing work over or near drains or sewers.
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