Cap flashing is specifically designed to prevent water intrusion at vertical surfaces. This type of flashing is installed at the top edge of a vertical surface, such as a wall or a chimney, where it intersects with a roof. The purpose of cap flashings is to direct water away from the vertical surfaces, preventing it from seeping into the building structure. The design features a projecting edge that helps divert rainwater, minimizing the risk of leaks and potential damage to the underlying materials.
Cant strips and casing flashings serve different roles in roofing systems. Cant strips are angled pieces that help create a smooth transition between the vertical and horizontal surfaces, improving water runoff but not specifically designed for sealing against water intrusion. Casing flashings, meanwhile, are typically used around windows or doors to create a waterproof barrier, but they aren’t exclusively intended for vertical surfaces like cap flashings.
A chalk line is simply a tool used to mark straight lines on surfaces and does not serve any purpose in preventing water intrusion. Therefore, cap flashing is clearly the appropriate choice for preventing water entry at vertical interfaces.