Replace old conservatory build over manhole

[britishbuilder]

Hello, I have a old, small, lean to conservatory (3.5mx2.25m). With one side beeing 10cm away from my neighbours fence. It is made of a pre cast concrete knee wall and 2mm glass and timberframe windows. The roof is polycarbonate. It was definitely build before 2011. The house us from 1967. I live in a mid terraced house, 2 houses left and 2 houses right. I realised that my conservatory is build over a manhole. One neighbour has a manhole in their patio and the other in their little extension.
My solicitor search at the time of house purchase said there are no shared sewer on the premises but as my neighbours waste goes through my pipes, I think it is. There is an indemnity insurance in place thfough the sewer survey. I would like to replace the conservatory on the existing concrete foundation. And add a double sealed manhole cover to maintain access which currently not have. The manhole is not visible at all. Moving it outside the conservatory is not possible due to a porcelain tiled patio. But I was reading I should request a build over agreement from my water company. But many people advised me against it. What if i request a build over agreement and don't get it? What is the best way forward? I am worried this will cause issues when I want to sell the house in the future.
Also, can I use a timber frame wall with composit cladding, pvc windows and a polycarbonate roof? Or do I have to use none combustible materials? I understand regulations that way, that the conservatory counts under permitted development and as it is under 15m2, it is building regulations excempt. And therefore I can use timberframe walls with external composite cladding. Is that correct?
Any advise is much appreciated!

 

[Wayners]

It's not unusual for a conservatory to be built over a sewer. People used to build over without planning but things have changed..
I'd go through the correct channels myself or any complaints will get you a knock at the door....
As for existing documents being incorrect. That's not unusual either. They didn't always put the sewer where it's shown on plans especially in 50s and 60s. Mine are wrong as well built 1964...

 

[foxhole]

Had a manhole in my last property conservatory ( terrace property ) .
Before extending had to remove the access and install drainage thru to interceptor and install new access outside my build line to satisfy water company ( Thames water ).

 

[stevie888]

Had this exact situation a couple of years ago. 2 chambers in fact as separate foul & SW. This was a corner plot and there was room to slew the 2 sewers out from the house, around the back of the new extension which involved turning back towards the house at the front as there was a side extension being done too. All in all 10 chambers to replace a pair. Fortunately there was enough fall in the existing to tolerate the additional length, We were also allowed to use PVCu: often you're expected to use clay if the existing is clay.

I fear this is one of those situations where you can't win. A few "repairs" would appear to be in order,

 

[britishbuilder]

I appreciate the comments. It is Anglian Water here. The only option I see would be a double sealed manhole in the conservatory. But some people told me that won't be allowed. Did anyone get a build over agreement with installing a double sealed manhole in the conservatory? The sewage pipe is clay pipe 100mm and he chamber is only about 80cm deep. The other option is i don't touch it and leave the conservatory as it is. I attached a drawing for visualisation.

 

[freddiemercurystwin]

They will most likely refuse a manhole inside.

 

[stevie888]

Now you've given us a picture it's a safe bet it will be a resounding no if you apply.

There is ample room to move the chamber: you just don't want to,

 

[britishbuilder]

Now you've given us a picture it's a safe bet it will be a resounding no if you apply.

There is ample room to move the chamber: you just don't want to,

Hello Stevie88, thank you for your comment. There are two aspects. I just got a new patio installed as I wasn't aware of any of that. And secondly, if i move the manhole to the left, it is less than 2m away from my neighbours manhole and that doesn't really make sense neither. Or am I missing something? If thats the only option, I am no opposed but it would be very expensive as I probably destroy the patio in the process.