Basin waste in en-suite

I've just putting the waste in place ready for the basin etc.

The shower and toilet are on one side of the bathroom and the vertical stack runs up the wall behind the toilet (50cm or so behind). So the pipework for the toilet is straight forward and the shower is simple enough with a short run of 40mm pipe.

However the small basin will be on the other side of the room. The room is about 3m wide, so from there the run of waste pipe will need to be about 3.5m.

I was considering running 40mm waste pipe for the basin due to the length, but then I was reading some guidance that said for anything over 3m it needs to be 50mm which seems to be a huge overkill for a small basin in an en-suite.

It needs to keep the BCO happy when he comes for his second visit.

Do you think 40mm will be OK?


Thanks

 

Never seen a BCO inspect pipes.
40mm is ok, only seen 50mm once shower, and basin pipes meet outside.