House extension - drainage plan/survey

lamialex

Hello,

We are in the process of building an extension on our house in London. The building company has told us we would need a drainage plan or do drainage survey if we can't get one because there is a manhole where the extension is gonna be. We bought the house 2 years ago and the solicitor had a plan of the drainage but we are not in touch with him anymore. He never gave us those plans. Where can we get those? Council? Thames Water? I tried the Thames Water website but very hard to find. Is it something we have to pay for? We want to avoid to do a drainage survey because obviously it's gonna cost more and we are pretty sure we saw this plan with the solicitor so wondering if there is a way to get it for free  or for little money. Thank you.

born_again

Ex next door neighbour had a manhole under a extension. Was fine till the pipe got blocked & sewage came out of it under the floor boards....
What a stink & mess that cost a fortune to sort out.
They didn't bother... But wished they had...

Albermarle

I understand that an internal drainage cover used to be allowed, but is not anymore.

maman

We're about to have an extension built to replace an existing conservatory. There is a manhole in the conservatory which fortunately has caused few problems and is accessible with the current ceramic tiled flooring. 

The new build will have underfloor heating so the manhole is to be moved outside the footprint of the building. 

Our architect/builder just wanted to know where the drainage was, where it lay from the manhole into the garden which we were able to show them as we've had work done previously . No survey required.

So I'd think a plan is what you need so they know where to find the drains. I'd try calling Thames Water and make enquiries.

Section62

lamialex said:

We are in the process of building an extension on our house in London. The building company has told us we would need a drainage plan or do drainage survey if we can't get one because there is a manhole where the extension is gonna be. We bought the house 2 years ago and the solicitor had a plan of the drainage but we are not in touch with him anymore. He never gave us those plans. Where can we get those? Council? Thames Water? I tried the Thames Water website but very hard to find. Is it something we have to pay for? We want to avoid to do a drainage survey because obviously it's gonna cost more and we are pretty sure we saw this plan with the solicitor so wondering if there is a way to get it for free  or for little money. Thank you.

Probably not worth wastingmuch time asking Thames Water.  Their mapping is primarily of main sewers - there is relatively little mapping of the smaller sewers in people's gardens which are either private, or "Section 24", or adopted in 2011.

If your solicitor cannot provide a copy of the plan then you would be well advised to just pay for a new drainage survey.  You need to find out what the manhole does and what pipes connect to it.  If any are public sewers then you'll need to get a buildover agreement with Thames Water.  If none are public then you will need this information to convince your BC that building over will be OK, or otherwise to plan (and estimate the cost of) moving the drains/sewers so they won't be under the extension.

If the builder changes their mind and says they will build over the drain/sewer anyway, or tries to convince you no buildover agreement is needed, then don't believe them without doing your own checks.  Lack of a buildover agreement is one of the things that causes headaches when people come to sell.

Green_hopeful

Many houses in towns have sewers that run from house to house in the back garden just outside the kitchen and bathroom. These then connect to the public sewers that usually run down the road. Prior to 2011 the back garden sewers belonged to the householders but the government decided they should belong to the water and sewerage companies. So by law they transferred over to the water companies. Normally the transferred sewers just run along the back of all the houses. A survey wouldn’t be complicated. It would probably just show the sewer coming from your neighbours and passing to the next neighbour and then to the public sewer in the road. 

I have assumed that your sewerage company is Thames water but it will be the same for all the companies. 

You can access Thames water’s statutory map either on their property searches website or at their Reading head office. If you go in person it is free to view but if you order the map there will be a charge. This leaflet is for developers rather than householder but there is a number to call and the Reading address.  https://www.thameswater.co.uk/media-library/home/developers/larger-scale-developments/planning/working-near-our-pipes/guidelines-for-working-near-our-water-mains-and-sewers.pdf Statutory map is unlikely to show transferred sewers because no one knows precisely where they are but sometimes they are shown. 

You could make an information request to your sewerage company to find out if there have been any issues with that sewer. They might give you a copy of the statutory map but they might just refer you to the website above. https://www.thameswater.co.uk/about-us/regulation/environmental-information-requests

if you want to build over the sewer you can apply to Thames Water for a build over agreement. https://www.thameswater.co.uk/help/home-improvements/building-over-sewers-or-public-drains

It is important to consider how you or the sewerage company would access the manhole if there was a problem as obviously you don’t want sewage in the wrong places. 

You can get a sewer diverted but I suspect that would be quite expensive. 

Archerychick

My water company (Anglian water) were really helpful in planning mine. We weren’t sure where the pipe ran (fortunately we don’t have a man hole cover in our property), and Anglian water came out and showed me where it was on their tablet, because they had the plans. He did say that they don’t have plans for everything sometimes you have to work it out from the man hole covers. 

I didn’t need a build over agreement, but you will need to move the man hole, Anglian Water will be able to confirm either way.