For a building with (4) six inch roof drains connected to an 8 inch main, what size vent is required?

In plumbing systems, venting is essential to ensure proper drainage and to prevent the siphoning of traps. The size of the vent required is typically based on the drainage system's configuration and the number of fixtures served.

In this case, four six-inch roof drains connected to an eight-inch main do not directly mandate an additional vent size based on the drainage capacity. The main drainage line's size is adequate to handle the flow from the roof drains without creating negative pressure that would require a vent of a specific size.

When the system is designed correctly with adequate drainage, additional venting may not be necessary, as the existing setup allows for the air needed to maintain the proper flow without introducing a vent line. This makes the answer 'None' appropriate because the current configuration does not require a separate vent piping installation to function effectively, provided it complies with other local codes and requirements regarding venting.

The option of a vent size such as 2-inch, 4-inch, or 6-inch suggests that there is a need for a vent when in fact, the design does not impose this requirement, given that the drains and the main line can work without extra venting. It's important to refer to the specific plumbing codes to confirm this, but typically