Adding a plumbing vent to old plumbing—too much work?

Ok plumber types. I understand why venting is now required, but many older systems lack individual trap vents. Moreover, older systems often have a single cast iron vent stack that… Ok plumber types. I understand why venting is now required, but many older systems lack individual trap vents. Moreover, older systems often have a single cast iron vent stack that…Read MoreGreenBuildingAdvisor