Several thousand to obtain a build over agreement?

[mike42]

Hi

I thought I'd ask here in case someone is kind enough to give some advice.

Our house is detached and has a garage next to it leaving a passage inbetween. There is a 4 inch sewer running underneath that and in the early 1990s, building control passed an extension which kind of builds over it (at first floor) but leaves the concrete passage in place at the existing external ground level.
Fast forward to now and we would like to build an extension which is about 600-700mm from that pipe at the closest point (please see attached drawings that I'd originally prepared to send to Thames Water).
As I understand it, there rules allow such an extension to be built but to get the actual agreement it seems that along with those plans, I would need to give them full "building regulations plans that were submitted to building control".
Now, we are at the feasibility stage and I was hoping I could give them my plans plus pay the £300 fee and get a decision. But if they want the full building regs plans (that don't exist now), presumably I'd first have to get and pay for planning permission (since no point doing anything until that is approved), then pay a structural engineer (at the very least) to get those plans.

So the questions I have are, is it virtually a foregone conclusion that they've give me the buildover because it seems to meet their criteria or would the existing work complicate things? Could I get them to give me an agreement without the full building regs plans on the assumption that my foundation design as is doesn't change?

Plan (Light shade walls is the existing house. Solid walls is the proposed extension at bottom towards left)
https://www.dropbox.com/s/kj22fpuimc1v4oy/site_plan.pdf?dl=0

Pipe section
https://www.dropbox.com/s/yqx5u5m2znuepgw/pipe_section.pdf?dl=0

Thanks in advance as ever for any thoughts on this!

 

[chappers]

is the sewer shared with anyone else?
You could always plead ignorance, but can't see them giving you much grief over that

 

[mike42]

Yes it is shared with three other houses. Also there are two internal manholes (!) that I mistakenly left off there that should go in the passage. I say "internal", because I'm not 100% if they are classed as such since the ground of that passage is the same level as outside and is rough concrete and the walls being the bare brick of the house and garage.
If I get refused is there any kind of appeal? I mean what is there to stop a water company just refusing everything since any work is only a possible risk for them without any upside?

 

[freddiemercurystwin]

Water companies publish guidance online as to what they will and won't approve and how it needs to be done, technically so it should be possible to assess it beforehand. In my experience no one will even look at it without the necessary drawings.

 

[chappers]

. In my experience no one will even look at it without the necessary drawings.

generally yes, but if you "just happen" to find a sewer during then works they do tend to have a more pragmatic/pro-active approach. you will still need to provide the relevant sketch, but you are more likely to get an indication straight away.

 

[mike42]

Well I rang TW and they suggested emailing them with the plans which I've done.

One thing I don't understand is why would they ever give anyone a builder over agreement? From their point of view, surely its just risk. Maybe there are some legal or regulatory rules that somehow compel then to give these agreements when appropriate? I haven't seen anything like that though and definitely not aware of anyone I could appeal to if they refuse.

 

[John D v2.0]

Build over rules are a bit like planning rules, it is all written down the specification and your job is to comply and their job is to certify that it will comply from your drawings. Plus a bit of paperwork and checking (and£££).
It's not a free choice thing for them and you can always take them to court if they misapply the rules.

 

[Ian H]

How deep is it? Even with the agreement I'd be tempted to replace it with new before building over it.

 

[chappers]

As I said before they won't give you a problem, your sewer invert is only half a meter below the ground level so you can build within 100mm provided your founds are below the invert of the sewer.

 

[Notch7]

I recently did a job that involved moving a public sewer for an orangery. Thames water were pretty helpful, albeit tricky to get hokd of.

Depending on the application, they may accept simple drawings showing foundation depth and position. They did for my project and didnt ask to see building regulation drawings.

 

[chappers]

I recently did a job that involved moving a public sewer for an orangery. Thames water were pretty helpful, albeit tricky to get hokd of.

Depending on the application, they may accept simple drawings showing foundation depth and position. They did for my project and didnt ask to see building regulation drawings.

Exactly they would just require a simple sketch, this would be a building regs sign off