i live in a three storey apartment building on the first floor. The apartment above me and mine often have terrible sewage smells in our bathrooms. It is not constant but comes and goes. We have recently found out that the plumbing vent that exits on the roof was modified as the owner of the penthouse didn't like where it came out on his roof terrace. Originally it was planned to come vertically out of the roof. Since the owner didn't like the location whilst the building was still under construction, he asked the builders to redirect the pipe. The builders then extended the pipe by using a ninety degree angle pipe and made the pipe go to the edge of the roof and then covered the pipe with concrete. The pipe is open at the edge of the roof. I would like to know if 1) this is ok per building rules and 2) Can the addition and angle of the vent pipe cause this awful smell we are having. What is the solution? To go back to the original plans? Thanks for your help.

if the vent pipe is open to the atmosphere it will work whether it is vertical, horizontal or anywhere inbetween.
only thing i can think of is strong winds affecting the free flow of air in the venting system ???

A horizontal pipe is often a good place for bee's or bird's nest. Have you confirmed that the pipe is open ?

It is probably NOT a factor, but if it exits horizontally wind blowing from that direction will create a positive pressure in the system.

Take a hose up and run water in the vent pipe to be sure that it is not blocked. Hopefully it is a 2" vent and make sure no bees are nested inside first. You can do that by observing the vent for 15 minutes or so. If it is 2" you will probably not have to worry about it being birds.