To Size Sanitary Plumbing Lines for Multiple Floors

Most sanitary systems are found in buildings that contain multiple floors, and each floor of the building is typically represented in a separate drawing. When sizing a sanitary system that spans multiple floors, you must size the plumbing lines for each drawing separately, starting from the highest floor and working downward. You can then reference the individual calculation values from the higher floors as you perform sizing on the lower floors.

To calculate a sanitary system in a 3-story building

1. Open the third-floor drawing and perform the following actions:
   

   1. Click the plumbing line closest to the second floor riser to select the run to size for the third floor.
   2. Under Design Values, verify that Branch is selected for Base Sizing On.
   3. Make a note of the calculated value for Fixture Units Upstream. You need to know this value for the subsequent steps.
2. Open the second-floor drawing and perform the following actions:
   

   1. Click the plumbing line closest to the first floor riser to select the run to size for the second floor.
   2. Under Design Values, select Offset/Home Drains for Base Sizing On.
   3. Enter the Fixture Units Upstream value from the previous step for Fixture Units from Branches Connecting Outside of this Drawing. The selected run is sized appropriately, and the value for Size of Plumbing Line is updated accordingly.
   4. Make a note of the calculated value for Fixture Units from Upstream Stack. You need to know this value for next step.
3. Open the first-floor drawing and perform the following actions:
   1. Click the plumbing line closest to the end of the main run that discharges out of the building to select the run to size for the first floor.
   2. Under Design Values, select Offset/Home Drains for Base Sizing On.
   3. Add the values for the Fixture Units from Upstream for the third floor (first step) and the Fixture Units from Upstream Stack for the second floor (second step).
   4. Enter the result for Fixture Units from Branches Connecting Outside of this Drawing. The selected run is sized appropriately, and the value for Size of Plumbing Line is updated accordingly.