Bridging sewer in footings

We're about to start a single storey extension and have to submit a build-over application to our local water authority (Severn Trent) as we're crossing a 150mm shared sewer pipe. The form says the application has to include a 'scale sectional drawing showing the footing and sewer'. Our builder says that until he's dug he can't tell us what he'd do, as that would depend on what he finds - he doesn't want to commit to anything until he knows what he's dealing with! Our architect was employed to do planning drawings, and seems to have stopped answering emails now that's all done and dusted!

The CCTV survey we've had done indicates that there are no issues with the sewer and that it runs across the footing as in the attached image. It leaves the manhole (bottom left of image) and will enter the footing at a depth of approx 1300mm and exit at approx 1800mm. The sewer runs in the footing for approx 1900mm.

Would the norm (with this information only) be to plan to dig the footing to level with the bottom of the pipe (1300mm one end, and 1800mm the other), shutter each end, pour the footing, then back-fill over the sewer with soil, then lay two lintels across the length of the filled-in opening, over hanging the concrete by 300mm each end?

Or wouldn't there be any need to fully excavate the footing above the sewer, and just either end and still do the same described above, but without the need for back-filling, but obviously still installing the lintels?

I'm thinking that this is my 'best guess' for submission purposes from the information I can gleam from the builder and how he's done thing like this in the past.

1974stephen said:

Our builder says that until he's dug he can't tell us what he'd do

Click to expand...

Then he is clueless. Literally and actually.

Dig out past invert level, shutter the pipe, concrete over it. Same every time.

You need a proper drawing for ST though. Like you must have a plan or something before you started. What did you submit to building control?

In my mind (as a layman in building terms) I thought he'd dig the footing, put some kind of pad stone at either end of the exposed pipe, building up some brickwork, lintel over the 1900mm length of the footing between the two brick piers / pad stones across the full 600mm width of the footing and then pour as normal, but he said it wouldn't be done that way.

It's an extended permitted development and our architect did a single planning drawing for that. We've been given building control 'permission' to proceed, but my understanding is that their first visit and any form of communication to site will be once the footings are dug, and technically I need approval from ST before we can start.

Mine was 1984 so I have no idea what's changed since.

the presence of the sewer was not known at the beginning and sadly we broke it before finding it. BC asked us to replace the 6" clay for the whole distance under the building of just under 6m needed to reach between inspection pit and convenient joint. It went right through the footings, BC expected the pipe to be protected with something soft. I had 10mm Jabolite, wrapped it with a couple of turns and fixed with gaffa. For good measure I dumped in a number of lengths of re-bar under and over pipe but not requested By BC.