How many branch intervals are permitted on a drainage stack for each attendant vent stack according to the CPD manual?

In the context of plumbing design, the regulation regarding the number of branch intervals on a drainage stack relative to vent stacks is important for ensuring proper venting and drainage performance. According to the guidelines set forth in the CPD manual, the maximum allowance is two branch intervals per drainage stack for each accompanying vent stack. This rule serves to facilitate effective venting while maintaining the system's integrity and performance.

The specification of "up to five in some codes" acknowledges that there may be variations in local or state plumbing codes that can permit additional branch intervals under specific conditions or scenarios. Such flexibility can be beneficial in unique installations, but it's crucial to adhere strictly to the primary guideline established in the CPD manual when designing plumbing systems.

This rule aims to balance the need for adequate drainage and venting to prevent issues such as siphoning and airlock conditions, which can negatively impact the performance of the plumbing system. Keeping the number of branch intervals within these limits is critical for maintaining system efficiency and ensuring compliance with plumbing standards.