Last updated 9th April, 2020
All you need to know about the removal of drains for an extension, including costs of surveying and scanning of drains, installation and moving drains, signing off, labour and time frames.
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.
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. 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.
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.
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.
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.
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|
Individual costs of a small drain removal for an extension - Total Cost: £1000