Build Over - Please can someone validate my drawings

[Dan Garfield]

Hi,

We're just about to get started on our extension and are trying to minimise costs by doing simple things and some plans ourselves. I did planning permission myself (approved), some builders are wanting quotes based on build over agreement with Anglian water for the sewer before we start, which needs technical drawings. Can some validate these for me!

* Depth to invert - 160cm
* Rough clearance between back wall for extension & sewer - About 56 cm
* We'll get the depth of foundations correct for building control, but just wanted to get the build over agreement sorted first, at a guess of 130cm, I'd prefer not to do foundations down to 160cm.
* We can't dig test as of yet, as the back garden is all concrete and I'll be getting rid of it in a couple of weeks
* Proper plans for building control will be done as part of the build (includes steels etc), I just want to get this build over agreement in place quickly for more accurate builder quotes

Request - Is the last image good enough?! Is a lintel ok? Do I need to go down to 160cm?

Thanks very much,
Dan

Note: The image above shows a slightly exaggerated angle of the public sewer and the original plan. Yellow = sewer. Red = manhole. No manhole on my property.

Note: White = original house. Blue lines = planned extension

Update: 175cm deep foundation option:

Note: Are you allowed to have a 'step' in the depth of foundations?

Thanks,
Dan Garfield

 

[wessex101]

I haven't checked Anglian but my local water company insist on foundation being taken 150mm below drain invert within 1 metre of drain.

 

[Dan Garfield]

Yes, I was hoping to avoid it, for completeness, I've just added a second section. Is it ok to be just within 60cm of a sewer with a parallel wall?

 

[wessex101]

I'm not sure why you show no foundation over the drain. Usually you only need to bridge the drain with about 300mm clearance (and not so wide). I tried to look at Anglian's guidance and couldn't find it do they have any? If not try a different company, Wessex Water have some details.

You can step the foundation, I cannot remember the figures look in Building Regs Approved Doc A.

 

[freddiemercurystwin]

Are you showing us these images because they are what you are actually going to submit to the water company? Or have you not yet drawn up the drawings yet?

My local water company also insist on the 150mm beneath the drain. They also expect a CCTV survey or complete exposure of the pipe to confirm its condition prior to the approval being issued.

There’s no point guessing the depth, the depth could easily have significant cost implications and may affect the foundation design.

And Building Control will expect a Full Plans Application where a Build Over is anticipated.

 

[Dan Garfield]

I'm not sure why you show no foundation over the drain. Usually you only need to bridge the drain with about 300mm clearance (and not so wide).

Are you meaning setting the lintel at a lower depth and concreting over the top / start course of bricks lower? I could only find these types of examples with lintel usage:
http://selfbuildextension.weebly.com/uploads/1/3/1/1/13111604/5308328_orig.jpg
https://www.diynot.com/diy/media/untitled.76192/full
https://developers.thameswater.co.u...-/media/5f1c4722ef414e92b4297b3519e4a75d.ashx

 

[Dan Garfield]

Are you showing us these images because they are what you are actually going to submit to the water company? Or have you not yet drawn up the drawings yet?

My local water company also insist on the 150mm beneath the drain. They also expect a CCTV survey or complete exposure of the pipe to confirm its condition prior to the approval being issued.

There’s no point guessing the depth, the depth could easily have significant cost implications and may affect the foundation design.

And Building Control will expect a Full Plans Application where a Build Over is anticipated.

100% agree. We will be going with a Full Plans Application, but builders are reticent to give detailed quotes without this agreement (I would prefer if they did). As we're building parallel to the sewer, I want to get an idea and ideally submit something to Anglian Water so that I know that it is not going to spiral out of control / get rejected later down the line. Our neighbours were absolutely fine and they even had to build over a manhole!

I will certainly take advice and if it's just not possible to get a build over agreement without digging / building control to validate foundation depths first, then I don't have a choice but to wait and do the building control at the same time. But this means builders the will be in and start to dig test trenches, but will only be able to start properly after a period of time waiting for the approval from Anglian Water. I know that the Building Control Body will not approve until the full plans application is in, but I wanted to attempt to address Anglian Water's concerns in advance.

I was planning to iterate over the next few days and start the ball rolling with Anglian Water. I would like to note on application stating that lintel heights / widths are subject to BC and structural engineer validation as well as the depth of the foundation (min. 150mm below invert).

How far off the mark is this?

 

[wessex101]

https://www.wessexwater.co.uk/Developers/Sewerage/Building-near-sewers/

there is a link on that page which will take you to the guidance notes. In a nutshell either set the lintels deeper in the foundation as shown or simply shutter around the drain and put some reinforcement in the foundation over the drain it all amounts to the same thing.

By the way the three examples on the links you posted all appear to be wrong. The internet can be a very dangerous place.

 

[Dan Garfield]

https://www.wessexwater.co.uk/Developers/Sewerage/Building-near-sewers/
there is a link on that page which will take you to the guidance notes. In a nutshell either set the lintels deeper in the foundation as shown or simply shutter around the drain and put some reinforcement in the foundation over the drain it all amounts to the same thing.

Thanks Wessex - I've looked at this and a few other guidance notes from other providers. I get the shuttering around the drain, that's good, thanks. I don't see how you interpret setting the lintels deeper from the Section C-C diagram and how this is any different from the last image that I added (175cm deep). As far as I can read it, the Section C-C doesn't contain any foundations above the sewer, only the lintel at an indeterminable height above. Unless I'm completely misunderstanding. But yes, I think I get your point, minimise the pea gravel 'gap' between the lintel and the sewer, but I haven't read anything on any guidance notes indicating that this should be the case. Hopefully that makes sense.

[LINKHL]1415[/LINKHL]
By the way the three examples on the links you posted all appear to be wrong. The internet can be a very dangerous place.

Yep, it certainly is! Although, one of those examples is actually from Thames Water.

 

[24sevenv24]

Hi! How did you get on with this build over application? Any issues? I am about to submit something very similar

 

[jeds]

I would start a new thread and provide some detail. Is your application with Anglian water?