When the roof slope is 3/12 or less, what is the minimum curb height required?

The minimum curb height required when the roof slope is 3/12 or less is 4 inches. This requirement is based on building codes and standards aimed at preventing water drainage issues and ensuring that any rooftop systems, such as HVAC units or ventilation systems, are adequately elevated to avoid water accumulation.

A roof slope of 3/12 indicates that for every 12 horizontal units, there is a rise of only 3 vertical units, which is a relatively low slope. Insufficient curb height can result in water pooling and may lead to potential leaks or damage to the integrity of the roofing system. Therefore, a higher curb height is necessary to ensure that any water can effectively drain off the roof rather than collect around mechanical equipment or flashings that could lead to long-term problems.

While other options suggest different heights, only the 4-inch curb height has been determined to provide adequate elevation in these low-slope conditions to mitigate any issues associated with water drainage. Thus, it aligns with existing guidelines seen in many construction and roofing projects.