On flat or gently sloped roofs, how far apart must mid roof air terminals be spaced at maximum?

The maximum spacing for mid-roof air terminals on flat or gently sloped roofs is crucial in ensuring effective lightning protection. By adhering to a spacing of 20 feet, it ensures that the air terminals can intercept lightning strikes effectively and provide a safe path for electrical energy to ground. This distance is determined based on the principles of lightning protection systems designed to mitigate the risk of lightning damage to structures.

Having air terminals too far apart could potentially create gaps in the protection, allowing dangerous lightning strikes to hit the roof without being intercepted. Therefore, the spacing is a critical factor in maintaining a comprehensive lightning protection system, and 20 feet represents a proven standard that balances effective coverage with practicality in construction and maintenance.