Manhole under where I want my extension to go!

[manholewoes]

I've been dreaming in an extension to my home for ages, have had architects round this week and they mentioned the manhole, which I hadn't really noticed as it's in my patio area and pretty well disguised.

I've pulled out the plans from when I bought the place a few years ago, and the plan seems to show that it's a shared sewers and I didn't realise that not everyone has a manhole in their garden.

I've attached a photo of the plans, pink arrow is my garden. The plans show that the manhole is what looks like a few metres
from my house, but it is about 1.5 metres away, I can't really extend a good amount (I originally wanted to go out 3.5 metres) to create another room.

Help! Do you think I might be able to get a build-over agreement (southern water) I know the only answer is to ring them, but it's Sat night and their phone lines aren't open and I'm not going to be able to sleep worrying about this!

We built our conservatory over the patio but it has an access hatch which is well disguised

I take it by your drawings you're a terraced house?

Hopefully you can sort it...but what you may not be able to do is put sharp bends in a public sewer as that is what can give a tendency to block....looks like,you need some time on the phone tomorrow with the water company

Yes like that , I don't see why that's not possible.

I don't think that will work as you will need a second manhole where the pipe joins again. You need a manhole each time there is a change of direction and the manhole must be outside the footprint of your extension. Easiest thing to do is to step your extension in from your boundary just enough to fit a manhole, and make all the connections from your existing drainage there.

That means I wouldn't get a utility room though small (or I would have to go outside to get to it) and I would lose a big chunk of floor space in the new living room, which is why I'm trying to find a way to divert the pipe & move the manhole.

Do you think the water company will try and work with me, or it is a bit "computer says no"?

If you need to make the extension narrower , but it wouldn't need to be that narrow a man hole is what half a meter across make the extension go further out so you are keeping sq m the same.

you don't want to have a sewer hatch under any part of your house - the rats will come up. shudder.

The water company will indeed try to work with you, they have an obligation to be reasonable, but their number one priority is to protect their network and their ability to maintain it.
You need advice from a professional but the long and short is no manholes in the property,a manhole at every bend or junction (that's why there are two close together already) and every section accessible with jets and cameras with sufficient clearance to work around it.
Having had a couple of blockages and seen what equipment they use i can see why they need space and access. They aren't trying to be difficult and some of the operatives are very creative!
In your case if you have enough available fall you can divert from the previous manhole to the next one. Just make sure it's all clearable.