What is the risk when using rusted, damaged, or deteriorated metal flashings on roofs?

Using rusted, damaged, or deteriorated metal flashings on roofs can significantly impair waterproofing. Flashings are critical components in roofing systems designed to direct water away from critical areas, such as joints and transitions, and to prevent leaks. When flashings are compromised due to rust or damage, their ability to effectively seal these areas is diminished, leading to potential water ingress. This can result in various problems, including water damage to the underlying structure, mold growth, and further deterioration of roofing materials.

While issues such as increased installation costs or decreased aesthetic value may arise from using poor materials, the primary concern is the loss of functionality—specifically, the failure to adequately protect against water infiltration. An increased fire hazard is generally unrelated to the condition of metal flashings in this context, as flashings are not typically linked to ignition sources or fire spread. Therefore, the most critical risk associated with using deteriorated metal flashings is the reduction in waterproofing capability.