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  • Writer's pictureKevin Maxwell

How to Size Your Own Plumbing Waste Lines.

Building a house from scratch also needs installing waste lines systems to provide water and remove waste. To get an idea of the type and size of pipes required for the drain, vent (DWV) system, waste, it's good to call the local building department for the plumbing codes. Many of the jurisdictions follow Uniform plumbing code requirements for the size of the pipe, but each jurisdiction may have deletions or additions to the code or use a particular year of the code. You can use these uniform plumbing codes to calculate the waste line size you need for the construction.


See the requirements in the codebook and compare them to the local building code requirements to make sure that both agree. If there is any difference make note of it. Get a good view of the home’s blueprint and assign the total number of units to each fixture as per the standards of the plumbing code table. For example, a toilet is known to have six units because of the amount of water it discharges. The number of units on one waste line pipe helps in calculating the size of pipe needed.

Now compare the fixture to the least size of drainage pipe by a fixture. If combined with a tub, the waste line pipe must be at least 2 inches in diameter. It is also important to know that the toilet requires a drain pipe of almost 3 inches in diameter. Add the number of units and compared it with the minimum pipe diameter for a particular fixture. Also, verify that the drain is not smaller than the biggest brand on the system.

Calculate the number of sanitary T-inlets and the combination of Y-inlets that tie into a stack on the system. It is easy to contact an expert plumber to do the waste line piping installation at your home rather than doing it all by yourself.

The Author Kevin Maxwell is the owner and operator of Maxwell Home Inspection Services, LLC. Kevin Maxwell is a certified Home Inspector located in Albany NY that has performed over 6000 Inspections.

Phone: 1-800-598-4754


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