How far apart can air terminals projecting 24 inches above the roof edge be spaced at maximum?

The maximum spacing for air terminals that project 24 inches above the roof edge is determined by standards set in lightning protection design. When air terminals, or lightning rods, are installed, their purpose is to intercept lightning strikes and direct the electrical energy safely into the ground.

For terminals that reach above the roof edge by 24 inches, industry standards typically allow for a spacing of up to 20 feet between them. This distance ensures adequate coverage of the area they are meant to protect, allowing them to effectively intercept potential lightning strikes.

Spacing terminals further apart would reduce their effectiveness, potentially leaving parts of the structure unprotected. The prescribed maximum of 20 feet promotes both safety and compliance with established lightning protection guidelines. Hence, the option that indicates 20 feet is the correct choice in this scenario.