What is the requirement for a vent stack in terms of sizing?

The requirement for a vent stack in terms of sizing is that it must be at least the same diameter as the largest drain it serves. This ensures that the vent stack can effectively allow air to enter the plumbing system, equalizing pressure and preventing siphoning of traps. A properly sized vent helps maintain the flow of wastewater and prevents the buildup of negative pressure that could lead to drainage issues or the loss of trap seals, which can allow sewer gases to enter the living space. This sizing requirement is critical for the proper function of the plumbing system and to uphold health and safety standards.