What Are Plumbing Riser Diagrams?
n the given picture, you can see a large waste pipe, and the cold and hot water supply pipes (marked blue and red respectively) leading to the position of the sink, indicated by a line drawing. The position of all of these, and all other relevant piping, will be shown on a riser diagram. However, only the water supply pipe is actually a riser.
The New York City (NYC) Plumbing Code defines risers as water pipes that extend one full story or more and convey water to a group of fixtures (like baths, sinks, showers, and lavatories) or to branches that extend to fixtures on two or fewer consecutive floors. Branches do not include risers, mains water pipes, or stacks, the latter of which are vertical lines of soil (for sewage), waste (water from fixtures and appliances, commonly called gray water), vents (to get rid of harmful gases), or inside conductor piping (for storm water).
However, it isn’t only risers that are included in plumbing riser diagrams, as you can see in Design of Plumbing Systems below. For instance, the NYC Department of Building (DOB) requires stacks to be shown on plumbing riser diagrams even though they are not risers! So too does the NYC Plumbing Code.