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Cost of Moving Drains UK: 2023 Extension, Conservatory etc.

All homes have underground drainage systems connecting the kitchen and bathroom to the main sewer. Unfortunately, if you decide to build an extension or conservatory, sometimes you must consider moving drains and their access points, manholes and gullies.

For a standard-sized drain, expect to pay, on average, £1500 to £3500, but estimates for more complex jobs can be upwards of £5000.  And, in the UK, other costs to apply for permission can easily add on £1500. However, there isn’t a fixed moving drain cost. It depends on the accessibility, complexity and size of the network.

You’ll find the same rules apply whether you intend to build an extension or a conservatory and that the prices won’t be very different. However, conservatories are usually more lightweight than extensions, so you won’t need such heavy-duty lintels when the drain pipe goes under the foundations.  In comparison, moving a drain in the garden won’t need specialist lintels or backfill. Therefore, this scenario will be even cheaper.

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How Much Does it Cost to Move Drains?*

The table below outlines typical drain relocation costs for different building scenarios in UK homes.

TaskEstimated cost rangeEstimated average
Moving drains for extension£600 to £3000£1500
Moving drains for conservatory£600 to £2500£1300
Moving drains in the garden£500 to £2000£1000
Permission from the local water company£300 to £1500£800

* We have compiled these figures from various online resources, with advice from professional drainage specialists. Remember that you can only get exact quotations if the contractor knows your drain’s location relative to the proposed work. Therefore use these costs as a starting point for your own research. 

Also, remember that your local water authority might refuse permission for specific reasons. Sometimes, it might be cheaper to move the position of the extension/conservatory so that building work doesn’t interfere with the existing drains.

Moving Drains for an Extension

Older houses, built before indoor toilets and bathrooms became commonplace, have vertical pipes accepting the bath and toilet waste pipes fixed to an outside wall. In contrast, recently built houses have all plumbing indoors and have drains running under the ground floor.

The drain from your house joins with other pipes at specific points using a manhole. You must not cover these inspection chambers, as engineers need access in case of blockage

Therefore, the primary job is to move manholes and other rodding access points to somewhere more accessible. In most cases, your contractor will do this while building the extension’s foundations and laying the concrete floors. At this stage, it is relatively easy for a skilled groundworker to continue the pipe under the extension’s floor and through the foundations, install a manhole outside the extension’s perimeter, and connect to other drains. However, if you build your extension over or within 3m of a public sewer, you must obtain permission from the water company. Usually, the water company’s engineers will base their decision on the level of risk to the existing sewer but are happy to work with householders and approve the build if the risk is small.

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Moving Drains For a Conservatory

The problems and risks to drains when building a conservatory are the same as an extension, with a few exceptions.

A conservatory is usually more lightweight than an extension, requiring smaller foundations. This has benefits where drain pipes go through the foundation blocks as they will need a smaller lintel. Alternatively, some conservatory manufacturers provide self-contained steel bases, which don’t need continuous foundations but are supported by a few concrete pads or foundation blocks. One such company ConservatoryLand® offers ConservaBase® as a solution to digging complete foundations. This product also has a removable access panel, so you can access a manhole if necessary.

The cost of a ConservaBase® depends on the dimensions of your conservatory, and whether you need an access panel. But for a no-frills 9m2 steel base, you can expect to pay from £1250 plus installation. However, you can save money with self-installation, as it comes with full instructions. This price might sound expensive. But, compared to the cost of rerouting drains, moving a manhole, or the risk that the water company declines your application, it’s worth every penny.

Remember, most conservatories don’t need to comply with Building Regulations. But, water companies will need to know if you intend to build near a public drain and will approve or reject your application depending on the risk. Check that your local authority and water company will accept a ConservaBase® on your project before you go ahead and buy one.

Moving Drains in a Garden

Moving drains in the garden will usually be for aesthetic purposes only. Perhaps a manhole cover interrupts the view across a beautiful lawn or flowerbed. Typically, moving a manhole will set you back around £1000 if it’s a simple job. And don’t forget the cost of getting permission from the water company.

The amount of work and cost also depends on its purpose, how messy the garden becomes, and what restoration work you need, as the ground may need landscaping, turfing and replanting. Furthermore, drain pipes under a lawn probably only need aggregate backfill, whereas if they’re under a driveway, you must bed the pipes into concrete to protect them from surface stresses and the weight of your car.

6 Moving Drains Cost Factors

When you decide to move drains, several factors affect the price.

1. Survey

Before anything else, you should have a CCTV survey of the existing drain. A survey involves:

  • A surface scan to find the pipe’s route.
  • Pushing a camera inside the drainpipe to ascertain its condition and view any problems.

Typically, a survey starts at around £250 and increases with the length of pipe run.

2. Materials

A standard pipe costs about £5/m. But, better quality pipes and specific types can be as much as £30/m.

You also have a choice of buying a plastic manhole and punching out the required number of drain inlets or building one the old fashioned way with brick, vitreous clay channels and mortar benching.

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3. Fees

Contact your water company and local Building Control office to confirm their prices.  Typically, the local authority charges £125 for the Building Inspector to sign off the work.

4. Labour

If you are good at DIY, it won’t cost a penny. But, be warned, rerouting drains, and building manholes is not easy. Unless you know exactly what you’re doing, you can cause many expensive problems.

A sewer pipe must have a gradient of between 1:40 to 1:110. If it’s steeper than this, the liquids will run away faster than the solids, leaving solids to dry out and block the pipe. In comparison, having a shallower gradient causes the solids to settle too soon. Other problems might occur, but remove them all by using a drainage professional. Trades charge around £250/day or £500-£750/job for a simple drain, while a more complex relocation can cost £2300 for materials and £1800 for labour. But it’s worth the price because professionals get the gradients and levels right every time. Also, many professionals can self certify their work; therefore, you won’t need a Building Control inspection costing £125.

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5. Distance

How far you relocate a drain and manhole will affect the price. This includes extra materials,  increased excavation waste material, more time getting the correct levels, and additional backfill.

6. Landscaping

After relocating a drain, the surface must look perfect. If it’s in a garden, the manhole lid must be flush with the finished lawn, and you must returf where you’ve excavated. This location is relatively simple. In contrast, if the new manhole is in a patio or driveway, you must repair excavations and inset the manhole into the hard surfaces, whether new concrete or pavers; it’s definitely a job for a professional.

Planning Permission & UK Regulation

Generally, you don’t need planning permission for minor drain repairs and maintenance. However, always check with your local authority to find out the rules in your area and what they class as “minor repairs”. Confirm who owns and is responsible for the drain before carrying out any modifications or relocations, as they might be shared with a neighbour or owned outright by your local water company. If you disregard this, you will be fined and must reinstate the drain at your own cost.

Remember that if your property is a listed building, any work, inside or outdoors, must have listed building consent.

The UK Building Regulations govern drains, and if you intend to build within 3m of a public drain, you need the water company’s approval. To submit a permit application costs from £300 to £1500. Although, you should ask the water company what their rates are before submission.

In the UK, there are two types of drainage:

  • Surface water drainage carries runoff from rainwater and snow shed from roof guttering and other outdoor surfaces.
  • Foul drainage carries the water and solids from toilets, sinks, baths, dishwashers, and washing machines.

In older houses, you might find that the two types are combined. However, in modern properties, they are kept strictly separate and must not join or empty into each other. Therefore, the first thing is to contact the water company and find out what type of drain you have. If you have a pipe that connects only your property to the public sewer, then the stipulations are far less severe than when the drain links multiple properties to the sewer.

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If you aren’t sure which water company controls the drains in your area, you can find out from here.


Can you build over a drain

If your drains are within the boundary of your land and serve only your property, you don’t need permission from the water company, although it’s a wise move in case of problems. And, it’s worthwhile finding out if it’s surface water or foul water drain.

Alternatively, if you share the pipe you want to build over with a neighbour, and the pipe is less than 150mm, you must seek permission from the local water company. If the pipe has a larger diameter than 150mm, you must contact your water company anyway.

Can I move a drain inspection chamber?

Unfortunately, sometimes it’s not that simple. If you reroute drains, you must provide additional inspection chambers (manholes) whenever the pipes change direction or join another drain. Then, you can remove any blockages that might occur. Therefore, you can’t only move an inspection chamber (manhole) without rerouting the pipework and removing the connection or bend that the manhole served.

How do I locate drainage and sewers?

There are maps available at the offices of your local water company and local authority. You can inspect them free of charge. However, private drains aren’t usually included in these maps.

Presumably, you have access to the site. If so, you can find the manhole covers, lift them, and decide where the pipes enter and leave the chamber. From this information, you should understand the pipes’ routes and depth. Do not enter the inspection chamber as toxic gases build up and cause unconsciousness.

Finally, you can hire a specialist company to do a CCTC survey of the pipes and present you with a diagram showing where the pipes run. The advantage of using this method is that you can see the drainpipes’ condition. Tree roots often find joints between pipes and force their way inside to get the water. As they grow, they will gradually destroy the pipes and cause collapse.

Find Local Drainage Specialists

Moving drainpipes can be very simple and done as a DIY project. Or, they might be very complex, in which case, you should choose a professional. Unfortunately, if you choose the DIY route and the job becomes very com[plicated, it will mean your home is without drainage for many days.

Therefore, from the beginning, it’s always a good idea to hire a professional drainage specialist to move drainpipes and install manholes. But, you need to know which company you can trust to charge a fair price and do a good job. Unless you know someone personally, you always run the risk of being scammed.

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