When must a skylight be mounted on a curb extending 4 inches above the plane of the roof?

The requirement for mounting a skylight on a curb that extends 4 inches above the plane of the roof is important for ensuring proper water drainage and preventing leaks. In general, a skylight should be mounted on a curb when the slope of the roof is less than 3 in 12. This is because lower slopes are more prone to water pooling, which can lead to potential leaks around the skylight.

When the slope is less than 3 in 12, the risk of water accumulating around the skylight increases, necessitating the higher curb to help divert water away from the opening. This design also allows for better ventilation and helps ensure that the skylight performs effectively without compromising the integrity of the roof system.

Understanding the relationship between roof slope and skylight placement is essential for compliance with building codes and for the longevity of roofing materials. Proper installation, especially on flatter roofs, promotes durability and minimizes the risk of moisture issues.