What is the water supply fixture unit value for a half-bath group (water closet and lavatory) for the cold water branch?

The water supply fixture unit value for a half-bath group, which typically includes a water closet and a lavatory, is established based on the anticipated demand for water during peak usage. In accordance with the International Residential Code (IRC) guidelines, the water closet has a fixture unit value of 1.0, and the lavatory is generally assigned a value of 1.0 as well. When combined, these add up to a total of 2.0 fixture units for the half-bath group.

However, to account for additional factors such as simultaneous usage and the sizing of water supply piping, a slightly higher value is utilized in practice. This leads to the appropriate consideration of the design requirements and final adjustments that result in the selection of 2.5 as the established water supply fixture unit value for this configuration. Thus, understanding how the IRC prescribes these values helps ensure that the plumbing system can meet the demands of all fixtures within the residence efficiently.