What construction practice is essential at the juncture of roofs and exterior walls?

Flashing installation is crucial at the juncture of roofs and exterior walls because this area is particularly susceptible to water infiltration. Proper flashing acts as a waterproof barrier that directs water away from critical areas, preventing leaks and water damage. This is especially important where the roof meets the wall, as the angle can create a pocket for water if not adequately addressed.

Flashing can be made from various materials, such as metal or rubberized asphalt, and its proper installation is key to ensuring that water flows away from the structure instead of seeping into the building envelope, which can lead to mold, rot, and structural deterioration over time. The effectiveness of flashing in managing water flow is a primary factor in preserving the integrity of both the roof and the walls, contributing to the longevity and durability of the building.

The other options, while important in their own right, do not address the immediate concern of preventing water penetration in this critical junction. Proper insulation, wall sheathing, and vapor barriers serve different roles, such as energy efficiency, structural support, and moisture control within the wall assembly, but they do not specifically address the direct need for waterproofing at the interface between roofs and walls like flashing does.