For a lavatory with an effective opening of ½ inch, what is the minimum required air gap when located close to a wall?

• A. 1 inch
• B. 1 ½ inches
• C. 2 inches
• D. 3 inches

Answer: (B)

The correct answer is 1 ½ inches for the minimum required air gap for a lavatory with an effective opening of ½ inch, especially in situations where it is placed close to a wall. This measurement is defined to ensure proper drainage and prevent back-siphonage, which can lead to contamination of the water supply.

The air gap serves as a physical separation between the outlet of the lavatory and the flood level of the fixture. The 1 ½-inch air gap provides sufficient height to safeguard against potential backflow, thereby maintaining the integrity of the water supply system. This standard is in accordance with plumbing codes that are designed to promote safety and health by preventing the possibility of cross-connection between potable water and wastewater.

Maintaining this distance is particularly important in installations that are in proximity to walls or other fixtures where back-siphonage could occur more readily. The requirement for the air gap reflects good plumbing practices to protect public health and maintain system functionality.