I am replacing my old shower in my first floor bathroom. The previous
waste pipe is vented by a long vertical piece of waste pipe into the
loft space above. I have never come across this sort of arrangement
before, and wonder if it is really necessary, as it's going to be a
real faff refitting it once the new shower tray is in. Any thoughts?
The only thing I can think of is that the shower waste pipe has about
3 metres to travel before it reaches a downpipe, so does not have much
of a slope, and that the venting is to improve the flow.

Keith