What is the primary function of horizontal wet venting?

The primary function of horizontal wet venting is to serve bathroom groups of fixtures arranged in a row. This method allows for the simultaneous venting of multiple fixtures, such as sinks, toilets, and showers, that are located close together. The horizontal wet venting system utilizes a drain as the vent for these fixtures, enabling air to enter the drainage system and prevent the creation of negative pressure that could disrupt the flow of wastewater. This setup is efficient as it minimizes the number of vents required and utilizes the existing drainage piping effectively.

In this system, as water flows from the fixtures, it fills the drain line which also acts as a vent allowing air to escape, thereby maintaining proper atmospheric pressure in the drainage system. This arrangement supports compliance with plumbing codes that require proper venting and ensures the functional and sanitary operation of multiple fixtures within the same room or on the same horizontal plane.