Massachusetts Plumbers Journeyman Practice Exam

When more than two four-inch soil or waste stacks are connected, what should be the diameter of the vent header extension through the roof?

1. Three inches in diameter

2. Five inches in diameter

3. Six inches in diameter

4. Eight inches in diameter

The correct answer is: Five inches in diameter

The appropriate diameter for the vent header extension through the roof, when more than two four-inch soil or waste stacks are connected, is determined by plumbing code requirements which are designed to ensure proper venting functionality. In this case, a five-inch diameter vent header extension is suitable for accommodating the increase in air flow necessary to balance the pressure and ensure that the waste can flow effectively without creating backpressure. This size helps to facilitate sufficient venting capacity, which is essential for the efficient operation of the plumbing system and prevention of potential issues such as siphoning of traps or the build-up of sewage gases. Selecting a diameter that is appropriate for multiple connections aligns with the best practices in plumbing design, aiming for enhanced outflow and reduced risk of clogs or drainage problems.