International Residential Code (IRC) Plumbing Practice Test

In a drainage, waste, and vent (DWV) system, the use of cement or concrete joints is prohibited due to the significant risk of creating an inflexible connection. This inflexibility can lead to stress and cracking in the pipe as it expands and contracts with temperature changes or ground movement. The integrity of a DWV system relies on the ability of the joints to accommodate such movements without compromising the system's function.

While other types of joints, such as metal couplings, welded joints, and PVC solvent cement joints, are permitted and widely used in DWV systems, they offer various advantages in terms of flexibility, seal integrity, and ease of use. Metal couplings allow for secure connections without risking damage to the pipes. Welded joints can provide a strong, durable connection for specific materials, and PVC solvent cement joints create a strong bond that can accommodate some degree of movement while ensuring a watertight seal. Thus, the prohibition of cement or concrete joints is rooted in ensuring the system's longevity and functionality.