A rear extension in Rugby can sit on top of a drain or sewer without anyone noticing until the groundworks start, and that is when a cheap quotation turns into a redesign. Whether you can build over the pipe depends on whether it is a private drain, a lateral drain or a public sewer, and Severn Trent Water has to agree to the last two before work begins. Planning permission and building regulations approval do not stand in for that agreement. This guide sets out the checks, the 3.0 metre measurement, what an application involves and what to ask a builder. It is general information, not advice on your own site.
The short answer
Check the drain before you fix the design
In Rugby, public sewers belong to Severn Trent Water, and building over or within 3.0 metres of one needs its written agreement first. Planning permission and building regulations approval do not replace it. A private drain serving only your house is simpler. Find and survey the pipes before the extension design is fixed, and ask every builder who applies and who pays.
Which drain is under the extension?
Start by finding out whether the pipe is a private drain, a lateral drain or a public sewer, because only the last two bring in the water company.
A rear extension in Rugby often goes where the house's drains already run, and the pipe you cannot see decides the whole route. Water UK's homeowner guide names three kinds. A private drain serves only your property inside your boundary. A lateral drain carries wastewater from a single house and meets the public sewer outside that boundary. A public sewer is a wastewater pipe that joins more than one property and connects to the existing network.
Rugby Borough Council's page on blocked sewers says Severn Trent Water has responsibility for public sewers in Rugby and that private sewers remain the responsibility of the homeowner or landlord. That tells you who to ask in Rugby, but it does not tell you which kind of pipe is in your garden. The Water UK guide adds that a lack of visible manholes proves nothing: if the house is connected to the public network, there is probably a sewer or lateral drain somewhere inside the boundary.
The practical first step is to find the pipes before the design is fixed. The Water UK guide suggests asking your architect or builder, reading the legal papers from your purchase for drainage details, and asking the water company, which may charge for locating pipes. It also points to digdatconnect.com if you do not know which company collects your wastewater.
Check the guidance: Water UK: building over or close to a public sewer or lateral drain, a guide for homeowners, Rugby Borough Council: report a blocked sewer.
When Severn Trent needs to be asked
Planning permission and building regulations approval do not give you consent to build over or close to a public sewer, so the water company is a separate check.
The Water UK guide is blunt: your work may need planning permission or building regulations approval, and some work falls under permitted development, but none of those permissions gives you automatic consent to build over, or close to, a water company's sewers. Severn Trent Water's own guidance says householders planning to build close to or over a public sewer have to seek permission, and that building close to or over one without formal approval is illegal. It adds that skipping approval may make the property difficult to sell.
How close is close? Severn Trent measures 3.0 metres from the nearest point of the building, foundations included, to the centreline of the sewer. Warwick District Council's page on building near sewers gives a looser everyday figure of typically 3 to 5 metres. Use Severn Trent's definition for the application and treat the council's range as a reason to ask early rather than a limit to design up to.
Rugby's building control is run by Warwick Building Control, a partnership between Rugby Borough Council and Warwick District Council. Warwick District Council's page says that for new buildings and extensions it checks sewer maps while processing an application and will tell you at the earliest opportunity if it finds a sewer nearby. That check does not replace your own application to the water company.
Check the guidance: Severn Trent Water: building over or close to public sewers, domestic extensions and garages, Warwick District Council: building near sewers, Rugby Borough Council: Warwick Building Control.
What the application involves
For a small domestic extension, Severn Trent asks for a CCTV survey, a scaled plan of the works and a fee, then issues provisional approval and a final letter after a second survey.
Severn Trent's guidance for domestic extensions and garages is written for homeowners extending over small sewers of 100mm to 225mm diameter. It says the company would prefer repositioning the extension or diverting the sewer, but is normally willing to permit building over or close to a sewer where the risk is small, diversion is not practical and the extension cannot be redesigned. Complex cases are handled separately.
| Class | What it covers | Fee shown |
|---|---|---|
| Class 1 | Sewers up to and including 150mm | £169.50 |
| Class 2 | 225mm sewers | £194.70 |
| Class 3 | Complex applications | At cost, contact Severn Trent first |
From survey to final letter
The sequence in the guidance runs in order. You establish the position, and preferably the condition, of the sewer, usually with a CCTV survey and electro location. You send Severn Trent the report and plans of the proposed works. If it accepts them, it issues a provisional approval, which may carry conditions. The building control officer separately checks the work against Part H4 of the Building Regulations 2010. When the works are finished, the sewer is surveyed again to show it has not been damaged, and you pay for any repairs. A final letter of agreement follows the survey or the repairs.
Severn Trent says it normally gives a decision within 10 working days of a complete application and that it cannot process an incomplete one. The survey must come from a competent contractor who produces a report to the standards the guidance names, and the contractor needs the company's permission to work on its sewer.
What counts as complex
The guidance lists what pushes an application into class 3. These are a formal easement in the deeds that prevents over-building, a sewer deeper than 3 metres, strategic sewers or sewers needing future upgrading, and piling or ground stabilisation works. A pressurised pumping main is in a category of its own: Severn Trent says it will not permit these to be built over.
Check the guidance: Severn Trent Water: building over or close to public sewers, domestic extensions and garages.
Building close to the sewer or over it
Within 3.0 metres the foundations and survey rules apply, and over the sewer you either replace the pipes under the footprint or survey before and after.
Severn Trent separates two situations. Building close to a sewer means within 3.0 metres, with depth measured to the underside of the pipe. For 100mm or 150mm sewers, no survey is needed before the work if you can show the accurate position of the sewer and prove that the foundation will not harm it. For a 225mm sewer, no survey is needed before the work if the sewer is no closer than 1 metre to the new building. In all other cases a CCTV and electro location survey is required, and every case needs a survey on completion.
Where foundations come within 1.0 metre of the sewer at any point, they must be carried down below the invert level of the sewer. At a greater distance, an angle of 45 degrees can be taken from a point one metre clear of the sewer up to the footing level. Depth is what makes this expensive in practice, because a deeper pipe means a deeper foundation, but the sources opened give no price for that, so we do not offer one.
Building over the sewer is stricter. Severn Trent says you can replace all public sewer pipes within the footprint at your cost, with manhole access for the post-work survey, or survey before and after and accept that localised repairs may be needed first. If an existing chamber, rodding eye or other access would end up inside the extension, a new manhole should be built on the line of the sewer outside the building, and connections inside the footprint should be diverted and reconnected outside unless that is impractical.
Check the guidance: Severn Trent Water: building over or close to public sewers, domestic extensions and garages.
When the sewer is not on the map
Older sewers may not appear on the water company map, so a Rugby extension can meet one only when the trench is dug.
Warwick District Council warns that sewers laid before 1937, and some adopted in 2011, may not be mapped, and that a sewer may only be found during building work. Its advice is that an application to Severn Trent is still needed if the work is over or within 3 to 5 metres of it. Severn Trent's own guidance says sewers built before 1 October 1937 that serve more than one property, known as Section 24 sewers, may not appear on its record plans.
For a homeowner in Rugby the lesson is to plan for an unexpected pipe, not to hope for none. Ask the designer to allow for a survey of the area before the foundation drawings are finalised. Ask the builder what they will do if a pipe or chamber turns up in the trench, who stops work, who contacts Severn Trent and who carries the cost of a redesign. If the sewer turns out to be where the extension must go, the options are the ones in the guidance: reposition, build over with protection, or divert.
Check the guidance: Warwick District Council: building near sewers, Severn Trent Water: building over or close to public sewers, domestic extensions and garages.
Timing, cost and what the sources do not say
The sources opened give application fees and a decision time but no price for a survey, a diversion or deeper foundations, so treat any figure you are given as a quotation to check.
The fees in the table are for the water company's application only. They exclude the CCTV survey, any pipe repairs, a new manhole, deeper foundations and professional fees, all of which depend on the site. Lanes Drainage Services, a contractor, published a guide to moving drains on 16 April 2024 that lists what affects the cost, such as the drainage design, site access and restoration of the garden, but gives no price figures. Treat that gap as a warning when you see a confident number on a quote.
Fees and distances differ between companies. Thames Water's page, which relates to a different water company, uses 3 metres from a public sewer and 1 metre from a public lateral drain, with fees of £130, £490 and £585 by pipe size, and it states no processing time. Those are not Severn Trent's figures and do not apply in Rugby. They show why a number copied from another area is not a safe basis for a budget.
Timing is the other cost. Because the agreement should be in place before work starts, an application made after the design is fixed can force a redesign. Severn Trent says a complete application normally gets a decision in 10 working days, but that does not include the time to commission a survey and obtain a report. Ask your builder to show the drainage checks as a line in the programme.
Check the guidance: Lanes Drainage Services: the cost of moving drains for an extension, Thames Water: do I need a build over agreement.
Questions to put to a builder before you sign
Ask every Rugby builder who finds the pipes, who applies to Severn Trent, who pays for surveys and repairs, and what happens if an unmapped pipe appears.
Drains are a classic gap between two quotations that look similar, so write the questions down and send the same list to each builder. Ask whether the quotation allows for a drainage survey and who commissions it. Ask who prepares and submits any application to Severn Trent and whether its fee is in the price. Ask whether the price includes a post-work CCTV survey and repairs the survey identifies, or whether those are provisional.
Ask for the drainage assumptions in writing: the position of any pipe, its size, and whether the foundation depth has been checked against it. Ask what happens if building control or the water company asks for a design change. A builder who has thought about this will answer clearly, and a builder who says drains are always fine has not looked.
Finally, keep the paperwork. Severn Trent warns that building without approval may jeopardise a future sale, and Thames Water's page, for its own area, says a missing agreement may block a completion certificate. Whatever the water company says about your address, a signed approval in your file is cheaper than arguing about it later. Building control for the extension itself in Rugby comes from Warwick Building Control, which is a separate application.
Check the guidance: Rugby Borough Council: Warwick Building Control, GOV.UK: Drainage and waste disposal, Approved Document H.
What clients say
Recent words from Belmax clients.
Three public five-star review excerpts, checked 24 September 2026.
“We have been really happy with the service from Belmax Builders. They are reliable, professional and, most importantly, always kept to the agreed schedule.”
“Belmax did the job to very high standard, communicated with us the whole time and explained really well what to expect.”
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Frequently asked questions
Can you build an extension over a drain in Rugby?
Sometimes. Where the pipe is a private drain serving only your house, building control is the main check. Where it is a public sewer or lateral drain, Severn Trent Water's guidance says it is normally willing to permit building over or close to small sewers if diversion is impractical and the extension cannot be redesigned. It prefers repositioning or diversion, and you need written agreement before starting.
How close can I build to a public sewer?
Severn Trent measures 3.0 metres from the nearest point of the building, foundations included, to the centreline of the sewer. Inside that distance you apply for permission, and foundations within 1.0 metre must go below the pipe's invert. Warwick District Council gives a looser range of typically 3 to 5 metres, so ask early if the extension is anywhere near a manhole or boundary line.
Does planning permission cover building over a sewer?
No. The Water UK homeowner guide says none of planning permission, permitted development or building regulations approval gives you automatic consent to build over or close to a water company's sewer. It is a separate application to the sewerage company, which in Rugby is Severn Trent Water for public sewers. Keep the approval letter with your building control papers because a buyer's solicitor may ask for it.
How much does a build over application cost?
Severn Trent's undated domestic guidance shows 169.50 pounds for sewers up to 150mm and 194.70 pounds for 225mm sewers, with complex cases charged at cost. That is the application only. It excludes the CCTV survey, repairs, any new manhole and deeper foundations, which vary by site, so check the current fee with Severn Trent before you budget for a Rugby extension.
What happens if I find a sewer while building?
Stop and ask. Warwick District Council says some older sewers are unmapped and may only be found during building work, and that an application to Severn Trent is still needed if the work is over or within 3 to 5 metres. Agree with your Rugby builder beforehand who contacts the water company, who pays for any redesign and how the programme will change.
Sources
Figures, fees and rules change. Every source below was checked on 11 November 2026.
- Severn Trent Water: building over or close to public sewers, domestic extensions and garagesUndated policy guidance, opened 11 November 2026: permission needed before building close to or over a public sewer; 3.0m rule measured from the nearest point of the building including foundations to the sewer centreline; class 1 fee 169.50 pounds and class 2 fee 194.70 pounds; decision normally within 10 working days of a complete application; CCTV survey after completion.
- Water UK: building over or close to a public sewer or lateral drain, a guide for homeownersUndated homeowner guide from Water UK and the water companies, opened 11 November 2026: defines sewers, lateral drains and private drains; says planning permission and building regulations approval give no automatic consent to build over or close to a sewer.
- Rugby Borough Council: report a blocked sewerOpened 11 November 2026: Severn Trent Water has responsibility for public sewers in Rugby; private sewers remain the responsibility of the homeowner or landlord.
- Warwick District Council: building near sewersUndated, opened 11 November 2026: building over or close to a public sewer, typically within 3 to 5 metres, needs an application to the water company; sewers laid before 1937 and some adopted in 2011 may not be mapped.
- Rugby Borough Council: Warwick Building ControlOpened 11 November 2026: building control in Rugby is run by Warwick Building Control, a partnership of Rugby Borough Council and Warwick District Council; telephone (01926) 456551.
- Thames Water: do I need a build over agreementOpened 11 November 2026, a different water company used only for comparison: 3 metres from a public sewer, 1 metre from a public lateral drain, different fees and no stated processing time.
- Lanes Drainage Services: the cost of moving drains for an extensionDated 16 April 2024, opened 11 November 2026: a contractor guide that names the 3 metre and 1 metre distances but gives no cost figures and no approval timescales.
- GOV.UK: Drainage and waste disposal, Approved Document HOpened 11 November 2026: statutory guidance for England on foul water drainage; the landing page shows a 4 December 2010 publication date and does not itself cover building over sewers.