Which types of flashing may be used when a roof system abuts a vertical surface?

The use of flashing when a roof system meets a vertical surface is critical to ensure effective water management and to prevent leaks. The correct response identifies apron flashing, step flashing, cricket flashing, and counterflashing as appropriate types in this scenario.

Apron flashing is installed at the bottom of a vertical surface to direct water away from the roof and prevent it from seeping beneath the roofing materials. Step flashing, which consists of individual pieces that interleave with the roofing material, is ideal for junctions where the roof meets a vertical surface, providing multiple layers of protection against water infiltration. Cricket flashing is utilized behind chimneys and other vertical structures to ensure that water is diverted around them, thereby preventing pooling. Lastly, counterflashing is positioned over step flashing to cover those seams and add an extra layer of defense against water intrusion.

In essence, these flashing types work together to create a robust system that effectively manages water flow at critical junctions. The other options do not include all the necessary components for this specific application, showcasing why the correct answer is the most suitable choice for roofing systems abutting vertical surfaces.