How high above the flood rim of a fixture must a vent be extended vertically before it can be run horizontal?

The requirement for vent pipes to be extended vertically above the flood rim of a fixture before running horizontally is crucial for maintaining proper drainage and preventing sewer gases from entering the living space. According to the plumbing code, this vertical extension must be at least 3 inches above the flood rim of the fixture.

This height ensures that any potential water backflow does not block the vent and that the vent functions effectively by allowing gases to escape. Additionally, it provides a safeguard against siphoning effects when fixtures are used, ensuring that the vent remains clear and functional, which is essential for maintaining proper pressure and drainage in the plumbing system.

Other height options (1 inch, 2 inches, and 4 inches) do not meet the specific safety and functionality standards outlined in the code, which is why 3 inches is the correct requirement.