Retrospective building regs on under tairs toilet

[MissClementine]

We have been in a house in SE for 7 years and one of previous owners fitted a toilet under the stairs but it has no building regulations sign off. A waste pipe was laid under kitchen floor to join the kitchen waste and there is a durgo fitted in the garden. It is fairly spacious and has a sink and an extractor fan. We are soon to refurbish the kitchen and we thought it would be a good time to update the toilet too. We would like to get building regs sign off for this in the process to ease future sale of house but as the waste pipe is buried in the floor I’m wondering how possible this would be?
Would we have to expose the waste pipe that was laid or would a camera survey be enough? I may contact BR department but thought I’d ask here first.

Building Control will be looking at two things, the pipe and the ventilation.

If you have a suitable extractor fan then that should be fine. As for the soil pipe, as long as it's 4" (110mm) then that will comply. They may ask for a drain test, but that's not so common now.

To be honest, regularising is best practice but after this amount of time it's not going to an issue unless you move or there's a problem.

Thanks, that sounds as though it could be straight forward. Without them seeing the pipe how would they know it’s dimensions and whether it’s deep enough under the floor?

Anyone else ever got building regs sign off retrospectively?