Types of Roof Flashing
Anyone knowledgeable in roofing will tell you that certain areas are more vulnerable to leakage and water damage than others. These areas, including places such as roof valleys, chimney perimeters or anywhere there's heavy runoff or different surfaces meeting, all are given an extra layer of protection against leaks. This protection, known as flashing, comes in a variety of materials for a variety of different purposes.
This type of flashing protects the joint space between a vertical wall and a sloped roof.
Step flashing protects chimneys, dormer side walls and, sometimes, skylights. It is shaped into a series of right-angle shaped pieces, with each section working to a course of shingles during the roof's installation. Each section of step flashing overlaps the section below it. The vertical edge of this flashing is usually tucked under siding or capped with a secondary counter flashing, mortared into the chimney or caulked along a skylight. This seal insures that water won't leak through the vertical edge of the flashing.
Chimney flashing is actually several types of flashing installed specifically to protect the base of the chimney. Continuous flashing is used around the bottom of the chimney, while step flashing is used up along the side of the chimney. Flashing is applied on the top, over the metal saddle, which cradles the chimney against the roof's slope. Cap flashing completes the seal over the rest of the flashing. This flashing is affixed over the top edges of all other flashing on the chimney and mortared or caulked into the chimney. The seal formed prevents water leakage behind the vertical edges of the flashing.
Most skylights actually have flashing integrated into their design, for easy installation. However, when this is not the case, the continuous flashing is installed along the base of the skylight, with step flashing up along the sides and saddle flashing across the top of the skylight.
When two roof planes meet, it forms a valley, and a vulnerable place for water flow. To prevent damage, a W-shaped channel of flashing is installed over the building felt, before the installation of the roof's finishing material. This is known as valley flashing.
Drip Edges Flashing
Drip edges are designed to prevent water from seeping under the roofing along the edges of the rakes and eaves. Drip edges are pieces of flashing installed underneath the roofing felt along the eaves and over the roofing felt along the rakes.
Vent Pipe Flashing
Vent pipe flashing is worked into the shingles as the roof is installed. It's purpose is to fit over flues and pipes and prevent leaks into them. This type of flashing is conical, with a flange at the base.