Build over agreement (sewer)

Swasterix

Good evening formers, me again! Hoping to pick your brains, hopefully for the last time (for a while). 

We had our architect round to survey our building this week for our proposed extension. We have a potential issue in that we have a sewer that crosses behind our house, bends and goes down our alleyway into the street. We were hoping to build double storey to the boundary on the side and single storey to the rear, which would likely mean building over the sewer. What complicates matters slightly is that the naughty previous owner built over the sewer when building our garden room. He didn’t have permission to do so and I have an indemnity policy in place. I realise this will be invalidated the moment I inform the water authority. He did assure me that it was built correctly with required lintels etc. although he could have been full of doo doo. 

I’m aware that we need to liaise with the water authority about our possible options. I’ve emailed them last week (not taking calls due to COVID), and haven’t had a response. I understand they’re fairly swamped at the moment so just wanted to get an idea of whether what we wanted to do was feasible, or whether any of you kind people had any better ideas. Or alternatively if it is a showstopper and we ought to stop spending money now!

Rough sketches, not to scale......
red- sewers/manholes
green- boundary
blue- proposed extension

current layout

Possible solution

TLDR - Sewer in the way of extension plans. Any ideas or are we snookered?

Doozergirl

That isn't a solution you've drawn.  Where you have a junction, you need an inspection chamber because it's a key point for a prospective blockage. 

Lots of councils don't like double
storeys to the boundary under their planning rules, so that might be another barrier.   Your pic probably isn't to scale but the space to the side looks very narrow anyway.  Perhaps the space can be gained elsewhere with good design. 

You probably want to concentrate on what you can do at the back.  We've not got enough info on what you want/need to start to suggest alternatives, but you're welcome to show us floorplans and ideas so far along with the want/need list.  As well as budget! 

Swasterix

Doozergirl said:

That isn't a solution you've drawn.  Where you have a junction, you need an inspection chamber because it's a key point for a prospective blockage. 

Lots of councils don't like double
storeys to the boundary under their planning rules, so that might be another barrier.   Your pic probably isn't to scale but the space to the side looks very narrow anyway.  Perhaps the space can be gained elsewhere with good design. 

You probably want to concentrate on what you can do at the back.  We've not got enough info on what you want/need to start to suggest alternatives, but you're welcome to show us floorplans and ideas so far along with the want/need list.  As well as budget! 

Hi Doozer, thanks for the response (as always!!). I did fear you would say that, as Id assumed the junction may be a problem...

The planning aspect isn’t a problem, we’ve submitted a one stop application with the council and all seems ok. What we are proposing to do is very common with this type of house on our estate. I have a 1m alleyway to the right of my property and will maintain at least 1m to the left with what we propose to do. 

It seems like the drainage may be the main showstopper. Do you think we have a way around it?

grumbler

Why not to redirect the neighbour's pipe under the remaining 1m then?

Swasterix

grumbler said:

Why not to redirect the neighbour's pipe under the remaining 1m then?

I did consider that, and then connecting in on my driveway, although I was reluctant as I didn’t want to inconvenience him too much. It’s his land so would need to try to sweet talk him.... maybe time to bake the fabled cake...

Assuming it’s doable, does everything else look ok?

Assuming it’s not, any other ideas?

grumbler

But the remaining 1m on the right side is yours, isn't it?

Swasterix

grumbler said:

But the remaining 1m on the right side is yours, isn't it?

Yes, that’s correct. 

grumbler

Then you can redirect it completely - under the right-side alley, then under your drive.

Swasterix

grumbler said:

Then you can redirect it completely - under the right-side alley, then under your drive.

Thanks Grumbler, that’s definitely an option. Although I’d still need to do something about the incoming connection from the neighbours. 

Finally got a call back from the Water Board today, they’re coming round next week. I will report back for future reference. 

Swasterix

Evening all. Thought I would revisit the thread to bring it to a close, in case anybody encounters something similar in the future. 

I had a visit from a nice chap from the water authority to discuss our plans. He was quite happy for us to build to the boundary (over the sewer to the side of the property), but advised that we would be required to re-route the sewer to the rear of the property, outside of the footprint of the build. We would also be required to re-route the neighbours drain to the rear so it could be connected to a new junction with manhole. 

Because of the scale of the works, we would be required to use their main contractor, a large civil engineering company (I think you can see where this is going here)......

Arranged a survey from the civils company. The chap spend the best part of 20 minutes sucking his teeth, telling me how it was going to be expensive, and taking the odd measurement. As he was leaving I asked him to give me a rough estimate, to work out whether the plan was feasible.... “you can’t hold me to this, it could possibly be more, but you’re looking at at least £20k.....”

I realised it would be expensive but, probably naively, not that expensive... I picked my jaw up off the floor, attempting to seem un-phased, wished him a good day, and arranged for the chap from the water authority to come back again...

After another discussion, he has confirmed he’d be happy for our builder to move the existing manhole at the rear closer to the boundary and fully build over the sewer to the rear, provided that we don’t build over the sewer at the side. Following a discussion with our architect to re-jig the internal lay out, we’re happy to go with option 2! Planning application goes in next week. 

TLDR - Anything is possible if you have the cash (and are prepared to spend it). However with a bit of imagination, there is always another cheaper (sometimes better) option. 

Thanks again to everyone who chipped in!