The photo below, taken at a new Florida home, is an example of what can be found wrong with new construction. That white pipe which is part of the plumbing system is called a plumbing vent pipe or stack. It is supposed to extend a foot or two above the roof. The purpose of this open pipe is to equalize the air pressure in the drain / sewage lines in the house so that they will drain properly. The plumbing vent pipe will help keep the plumbing drain traps under the plumbing fixtures from having water siphoned out of them. The water in the plumbing traps prevents sewage gas from entering the house. Not only was this vent pipe covered over with a roof shingle, there was no flashing around it to prevent water from seeping down around in into the house.