Build over agreement- existing drainage info

[Richard Marin]

Good afternoon all, 

 

I have submitted a build over agreement application and they have come back with the following query:

 

Your application was missing the following:

 

Proposed building drainage layout plan

 

Ground floor plan showing proposed private connections onto the sewer.

 

Where can I get my existing drainage plan information for my house? Builder said he can't start the job until this is in place.

 

Please help :-)

 

 

[saveasteading]

Firstly look at your deeds, just in case

 

 

Annoyingly the next dource is the drainage company, so it seems they don't know. Maybe phone and ask. 

 

Next,  you draw it yourself  you may need your builder to lift manhole covers, especially if in the road.

Come back for more info of what you will have to look for and report.

 

Do you at least have info on the drain you want to build over? Posting it on here would allow more help.

[Richard Marin]

Thank you for you prompt response. I have attached the drain in question from the initial information we received when we bought the house. I will speak to the builder and see if he can assist in the meantime I will see if I can ask the local council or a drainage company like you suggested.

[saveasteading]

So we now know that this is a 150mm diameter combined drain (ie carrying both rainwater and sewage.

And that in nextdoor's garden there should be a manhole cover

 

The water company will have this same drawing, with additional info. Ask them for the full drawing, and btw isn't this sufficient to deal with their own question?

Anyway you need the full drawing from them. It will have a table with all the drain and manhole cover levels

[Gus Potter]

48 minutes ago, Richard Marin said:

I have attached the drain in question from the initial information we received when we bought the house.

Hi Richard.

 

You're going about this the right way.

 

4 minutes ago, saveasteading said:

So we now know that this is a 150mm diameter combined drain (ie carrying both rainwater and sewage.

Yes good info and probably the starting point really to make progress.

 

I have designed a few solutions for build over permission where we have a run of houses with the public sewer running up the back of the houses, very similar to yours... it can be done with a fair wind.

 

In some ways having the old combined system can be a blessing as you only may have to make one connection and maybe blank off other existing ones. However, depending on where you are some water companies are not keen on you adding rainwater flow to the combined system as this exacerbates the problem with stormwater overflows spilling into rivers. At some point they may or may not ask for flow calculations. Leave that for now as it is in itself a lengthy topic. There are loads of folk on BH that know a lot about this, ask if you need to.

 

For all... generally. A private sewer is a drain you do not share.. you own it. A public sewer serves more than one house and generally the water company own that. These public sewer run into main sewers.. often the big one in the road. In this case the drain being build over is a public sewer. There will be branches in the public sewer that connect into your bit of drain from your own house. You generally own (private sewer) the upstream bit from the branch socket.  Also, as this is a combined sewer your rainwater pipes will be trapped and then connect into the public sewer. This is relevant later once you get into the detailed design as you often find that the trap and other connections start to obstruct founds etc and you compromise the ability to rod the drains. You may be lucky and find that the rain water down pipe serves both houses and the trap is on your neighbours side.

 

I recently designed something like this in Scotland, similar rules apply in parts of the rest of the UK.

 

This is the Scottish Water compliant method I used to get the build over permission. The line of houses were on a slope and the gardens were terraced. The manholes were away from the site.. I could roughly figure where the drain might be but not how deep as did not know the fall and also folk had been regrading the gardens over time.

 

 

1/ @saveasteading, yes I got the plan which indicated the MH covers and invert levels. That got me on the ball park. The main thing to recognise is that the record plans are often far from accurate and ofetn incomplete.

 

2/ The Client knew that the neighbour had a MH cover in their garden that was not buried under flower borders etc so after asking nicely we were allowed to lift the cover. Good news the invert level was not too deep. The year before I had one where we lifted the cover and could nearly see Australia. After a bit more investigation we abandoned the job as the drain was so deep it needed an expensive structural / gorund solution to deal with that and a couple of other things that just made the project uneconomic. At least we found out early on! Everyone was dissapointed, including me.

 

3/ Next was to get an approved Scottish Water company to do a CCTV survey. This was one of their (SW) requirements.  We put the camera into the neighbours MH and fed it uphill to about 1.5m beyond the far boundary. The equipment they use is pretty good. Now we knew the line of the drain and the depth to about + / - 200mm. We could also see where the branches were connecting in. Importantly we were able to assess the condition of the drain and how good the joints were. Some of the joints were leaking and there was a bit of ground water seapage into the sewer. You could see a couple of little water spouts! Anyway the CCTV guys said.. not bad and the drain looks ok, SW should be happy with that. The CCTV folk do a formal report, a sketch plan with some dimensions. They also send a natty video and at the bottom you can see the calibration so you know where the camera is. The camera gets a bit of a hard time as it's amazing how often folk flush their toilet. This give you confidence to make the next step.

 

4/ We  next hand dug a pit to check the CCTV info. Found the drain and the rainwater pipe trap which was bang up against the boundary retaining wall. Because the drains were at an angle it was clear that we needed to design the founds for this. But at least we knew what was what and could plan for that rather than risking problems during construction.

 

5/ Next was to design the drainage layout, prepare the drawings and then submit the CCTV survey package and the drawings for SW approval. Part of the approval was conditional on us getting a post construction survey. Screen shotted below is part of the build over approval so you can see what kind of thing the water companies are looking for.

 

 

Ok that is.. call it the permission side / admin. But what sort of drawings do you need and how to design a build over up the back of of say @Richard Marin's house?

 

My starting point is to go to the Sewers for Scotland guidance. It has a diagram that shows the zones where you can do stuff. You'll see lots of similar diagrams produced by water companies over the UK.

 

 

 

 

Next was to marry this up with the site levels, look at options and get the best drain layout that suited the actual thing we wanted to build, in this case a rear extension. I have attached the two drawings that were submitted along with the CCTV survey to support the application for build over permission. I have edited them a little to remove identifiable info, if I have missed something can folk let me know?  All drawings need a title box, sometimes it's good to let folk turn on and off the layers if using pdf.

 

There is a fair bit of useful info on the drawings that lets you see the level of information that results in a good application. Hopefully they give you food for thought and point you towards what you need to know about your project.

 

Please bear in mind though.. there is a bit of my IP in there which I don't mind sharing as I learn loads from BH and enjoy the enthusiasm here. One important thing is that these drawings show part of the foundation design. What they don't show is the structure above and how that fits with drawings you see. For example the drawings take into account the loading from above, building stability, soil pressure bulbs, what impact these will have on the existing house founds and the retaining wall adjacent to the existing house founds. In other words don't just copy the info and hope for the best.. or you will end up in trouble.

 

Just to finish. You may be thinking.. is this overkill from Gus and how much does is that type of application going to cost me?

 

Cost.. not as much as you think... probably the wrong phrase to use if in say Yorkshire.  Good planning like this keeps the build cost down and reduces the risk of the unforseen. The dreaded "invoice from the builder for extras".. which they have a habit of submitting when they know they have you over a barrel, risk is reduced.

 

But also you put loads of time, effort, invest your emotions.. and money into something like this and do it right. But what if your neighbour builds out the back, they are gung ho, damage the drains and put your extension at risk.. Oh.. now that post condition survey suddenly comes in handy, especially as it went 1.5 m beyond your boundary. Think of this CCTV survey as buying a bit of insurance.

 

@Richard Marin Hope this gives you a bit of insight and allows you to pick the best bits that suit you and disregard the rest.

 

Keep us posted and all the best with the project.

 

 

 

 

 

 

 

 

 

 

 

 

DRG-SW01 Foundation and Drainage Layout A2.pdf DRG-SW02 Rev01 Drainage and Cross Sections A2.pdf

[Richard Marin]

16 hours ago, saveasteading said:

So we now know that this is a 150mm diameter combined drain (ie carrying both rainwater and sewage.

And that in nextdoor's garden there should be a manhole cover

 

The water company will have this same drawing, with additional info. Ask them for the full drawing, and btw isn't this sufficient to deal with their own question?

Anyway you need the full drawing from them. It will have a table with all the drain and manhole cover levels

That's exactly what I was thinking as well 😊 ....thank you

[Richard Marin]

13 hours ago, Gus Potter said:

Hi Richard.

 

You're going about this the right way.

 

Yes good info and probably the starting point really to make progress.

 

I have designed a few solutions for build over permission where we have a run of houses with the public sewer running up the back of the houses, very similar to yours... it can be done with a fair wind.

 

In some ways having the old combined system can be a blessing as you only may have to make one connection and maybe blank off other existing ones. However, depending on where you are some water companies are not keen on you adding rainwater flow to the combined system as this exacerbates the problem with stormwater overflows spilling into rivers. At some point they may or may not ask for flow calculations. Leave that for now as it is in itself a lengthy topic. There are loads of folk on BH that know a lot about this, ask if you need to.

 

For all... generally. A private sewer is a drain you do not share.. you own it. A public sewer serves more than one house and generally the water company own that. These public sewer run into main sewers.. often the big one in the road. In this case the drain being build over is a public sewer. There will be branches in the public sewer that connect into your bit of drain from your own house. You generally own (private sewer) the upstream bit from the branch socket.  Also, as this is a combined sewer your rainwater pipes will be trapped and then connect into the public sewer. This is relevant later once you get into the detailed design as you often find that the trap and other connections start to obstruct founds etc and you compromise the ability to rod the drains. You may be lucky and find that the rain water down pipe serves both houses and the trap is on your neighbours side.

 

I recently designed something like this in Scotland, similar rules apply in parts of the rest of the UK.

 

This is the Scottish Water compliant method I used to get the build over permission. The line of houses were on a slope and the gardens were terraced. The manholes were away from the site.. I could roughly figure where the drain might be but not how deep as did not know the fall and also folk had been regrading the gardens over time.

 

 

1/ @saveasteading, yes I got the plan which indicated the MH covers and invert levels. That got me on the ball park. The main thing to recognise is that the record plans are often far from accurate and ofetn incomplete.

 

2/ The Client knew that the neighbour had a MH cover in their garden that was not buried under flower borders etc so after asking nicely we were allowed to lift the cover. Good news the invert level was not too deep. The year before I had one where we lifted the cover and could nearly see Australia. After a bit more investigation we abandoned the job as the drain was so deep it needed an expensive structural / gorund solution to deal with that and a couple of other things that just made the project uneconomic. At least we found out early on! Everyone was dissapointed, including me.

 

3/ Next was to get an approved Scottish Water company to do a CCTV survey. This was one of their (SW) requirements.  We put the camera into the neighbours MH and fed it uphill to about 1.5m beyond the far boundary. The equipment they use is pretty good. Now we knew the line of the drain and the depth to about + / - 200mm. We could also see where the branches were connecting in. Importantly we were able to assess the condition of the drain and how good the joints were. Some of the joints were leaking and there was a bit of ground water seapage into the sewer. You could see a couple of little water spouts! Anyway the CCTV guys said.. not bad and the drain looks ok, SW should be happy with that. The CCTV folk do a formal report, a sketch plan with some dimensions. They also send a natty video and at the bottom you can see the calibration so you know where the camera is. The camera gets a bit of a hard time as it's amazing how often folk flush their toilet. This give you confidence to make the next step.

 

4/ We  next hand dug a pit to check the CCTV info. Found the drain and the rainwater pipe trap which was bang up against the boundary retaining wall. Because the drains were at an angle it was clear that we needed to design the founds for this. But at least we knew what was what and could plan for that rather than risking problems during construction.

 

5/ Next was to design the drainage layout, prepare the drawings and then submit the CCTV survey package and the drawings for SW approval. Part of the approval was conditional on us getting a post construction survey. Screen shotted below is part of the build over approval so you can see what kind of thing the water companies are looking for.

 

 

Ok that is.. call it the permission side / admin. But what sort of drawings do you need and how to design a build over up the back of of say @Richard Marin's house?

 

My starting point is to go to the Sewers for Scotland guidance. It has a diagram that shows the zones where you can do stuff. You'll see lots of similar diagrams produced by water companies over the UK.

 

 

 

 

Next was to marry this up with the site levels, look at options and get the best drain layout that suited the actual thing we wanted to build, in this case a rear extension. I have attached the two drawings that were submitted along with the CCTV survey to support the application for build over permission. I have edited them a little to remove identifiable info, if I have missed something can folk let me know?  All drawings need a title box, sometimes it's good to let folk turn on and off the layers if using pdf.

 

There is a fair bit of useful info on the drawings that lets you see the level of information that results in a good application. Hopefully they give you food for thought and point you towards what you need to know about your project.

 

Please bear in mind though.. there is a bit of my IP in there which I don't mind sharing as I learn loads from BH and enjoy the enthusiasm here. One important thing is that these drawings show part of the foundation design. What they don't show is the structure above and how that fits with drawings you see. For example the drawings take into account the loading from above, building stability, soil pressure bulbs, what impact these will have on the existing house founds and the retaining wall adjacent to the existing house founds. In other words don't just copy the info and hope for the best.. or you will end up in trouble.

 

Just to finish. You may be thinking.. is this overkill from Gus and how much does is that type of application going to cost me?

 

Cost.. not as much as you think... probably the wrong phrase to use if in say Yorkshire.  Good planning like this keeps the build cost down and reduces the risk of the unforseen. The dreaded "invoice from the builder for extras".. which they have a habit of submitting when they know they have you over a barrel, risk is reduced.

 

But also you put loads of time, effort, invest your emotions.. and money into something like this and do it right. But what if your neighbour builds out the back, they are gung ho, damage the drains and put your extension at risk.. Oh.. now that post condition survey suddenly comes in handy, especially as it went 1.5 m beyond your boundary. Think of this CCTV survey as buying a bit of insurance.

 

@Richard Marin Hope this gives you a bit of insight and allows you to pick the best bits that suit you and disregard the rest.

 

Keep us posted and all the best with the project.

 

 

 

 

 

 

 

 

 

 

 

 

DRG-SW01 Foundation and Drainage Layout A2.pdf 202.07 kB · 0 downloads DRG-SW02 Rev01 Drainage and Cross Sections A2.pdf 301.8 kB · 0 downloads

Thank you so much this is very useful ans I appreciate the time you have taken to write this information. I will review in more detail and take some of the points which will further assist with the application. I will keep you all posted on process.

[saveasteading]

On the phone or email tomorrow Tell us how you get on.

 

It would be great to know ASAP about the depth

 

If you are friendly with the neighbour. All you have to do is lift off the manhole cover. It might need special keys from toolstation screwfix or wickes.

 

You will see the drainage channel

Put a piece of timber across the hole, resting on the manhole frame. Then measure down to the bottom of the channel.  This is known as the invert. take pictures. Then tell us what you find and see.

What is the manhole made of? Brick, concrete or plastic?

 

Put the cover back on.

 

With that info we can look further ahead.

 

Edited June 18, 2023 by saveasteading

[saveasteading]

15 hours ago, Gus Potter said:

don't just copy the info and hope for the best.. or you will end up in trouble.

Indeed this reminds me of a main contractor client who pinched an idea from me, trustingly offered pre_tender.

There were swings and roundabouts and so they way underpriced.

To their credit their director admitted this and the naughty surveyor was soon gone.

 

You will need professional input, we only offer advice and ideas