Underground drainage connections

[collings]

We are doing an install of 4 toilets in the basement of what will be a new bar. (Victorian Building). We cannot get the Regulation 450mm between the pan outlets as the existing 4 inch clay pipe is only 300mm below finished surface at it's lowest point before it enters public sewer. I want to run a 3 metre length of underground pipe with tees and each pan then connecting to these via short vertical drops into the underground pipe. There will be an inspection chamber at the low-point where it then runs off to the public sewer and also an AAV.

Are there regulations saying in a basement we can get away without the 450mm or that because the clay pipe is existing and we cannot change it? It is impossible to dig down further as we would be below the public sewer. (don't anyone dare mention macerators!)
Thanks

 

[doitall]

Ask building control what they'll let you get away with.

 

[collings]

Yes I'll talk to the client. Building Control have not been since we dug out the cellar floor. Think they're due back to check out the staircases soon but I can't see them telling us we can't be the toilets down there. Plans have been submitted to LA and nothing was said then and it must be obvious that a basement in the town centre must have shallow drains.....

Why is this 450mm anyway?

 

[doitall]

I have no idea, probably what some suit dreampt up.

 

[Nige F]

part of the dark art of plumbing like the 1:40 fall on every pipe that carries waste water . The 450mm is as far as I know to do with a single stack soil/vent setup and compression of air/water @ the bottom of a stack The 1:40 is a rule of thumb fall in a 4 inch drain pipe ( from when they were 2 foot long salt glazed pipes . There is such a load of old bull.... that goes with plumbing/ drainage Building Control should be sensible enough to see the constraints of the job.