During a renovation, a plumber needs to extend an existing 4-inch (100 mm) cast iron DWV stack for a new fixture. The connection must be made without disturbing the lower sections. Which joining method is best suited for this application, assuming access to only one side of the joint?

Question: During a renovation, a plumber needs to extend an existing 4-inch (100 mm) cast iron DWV stack for a new fixture. The connection must be made without disturbing the lower sections. Which joining method is best suited for this application, assuming access to only one side of the joint?

Answer options: ✅ No-hub coupling (shielded hubless coupling)

• Caulked bell-and-spigot joint
• Solvent-welded joint
• Threaded joint

Correct answer: No-hub coupling (shielded hubless coupling)

Explanation: A no-hub coupling is ideal for connecting cast iron pipes without needing access to both sides or the specialized tools for caulked joints, making it suitable for renovation work where existing pipes need minimal disturbance. Caulked joints require a bell end and pouring lead, solvent welding is for plastics, and threaded joints are not typically used for DWV cast iron pipes in these sizes.