The required size of branches and risers shall be permitted to be obtained in the same manner as the building supply, by obtaining the demand load on each branch or riser and using the permissible friction loss computed in Section A104.0.
Where fixture branches to the building supply are sized for the same permissible friction loss per 100 feet (30480 mm) of pipe as the branches and risers to the highest level in the building and lead to the inadequate water supply to the upper floor of a building, one of the following shall be provided:
- Selecting the sizes of pipe for the different branches so that the total friction loss in each lower branch is approximately equal to the total loss in the riser, including both friction loss and loss in static pressure.
- Throttling each such branch using a valve until the preceding balance is obtained.
- Increasing the size of the building supply and risers above the minimum required to meet the maximum permissible friction loss.
The size of branches and mains serving flushometer tanks shall be consistent with sizing procedures for flush tank water closets.