Flashing is a flat metal added in sheets along corners, seams, and edges of roofs to prevent leaking and direct water towards gutters. Roof flashing is usually made from rust-resistant metal, like galvanized steel, copper, or aluminum. Anywhere where water may run or collect, flashing can usually be found on the edges and underneath the shingles or other primary roofing material to assist in drainage and leak prevention.
Flashing is installed in vulnerable spots on the roof, including valleys, which is where two planes of the roof join, on the side and bottom edges of the roof, around chimneys or dormer windows, around skylights, and around vent pipes or other outlets.
Types of Flashing
Base and Counter Flashing
This type of flashing is often installed around chimneys, dormer windows, and other spots with a structure coming straight up out of the roof. One piece of flashing is placed on top of the roof surface at the base of the structure (the base flashing), and another is placed along the side of the structure at a 90-degree angle to the base flashing (counter flashing). These two pieces paired together provide protection against water leaking through the seam between the roof and the gable or chimney.
Chimney flashing usually consists of a combination of step flashing, continuous flashing, and back pan flashing. Step flashing is bent at a 90-degree angle and laid in overlapping pieces along the side of the chimney, while continuous flashing is laid at the lower edge of the chimney. Back pan flashing is built up on the side of the chimney closest to the ridge of the roof, and forms a peak that directs water to either side of the chimney.
Continuous roof flashing is a long piece of flashing at the bottom edge of a chimney, dormer window, or skylight. This piece of flashing directs water down away from the structure and towards the gutter. If this piece is too long, it can experience stress when the roof expands with weather changes. Therefore, long pieces of continuous flashing are constructed with expansion joints that allow the flashing to move with the building.
Flashing is laid under the shingles on the edges of the roof to prevent water from seeping under the roofing material. This can be along the eaves, which are along the lower edge of the roof, or rakes, which are the outer edges along a gable, from the eave to the ridge.
Most skylights come with their own flashing installed, which surrounds the window and prevents water from leaking through on the edges of the skylight. In rare cases, a roofer will need to add flashing to the edges themselves. The flashing is placed under the shingles on the sides and over the shingles on the bottom edge to allow water to run around the skylight instead of leaking into the seams between the skylight and the roof.
Valley flashing is placed along valleys on the roof, where two planes of the roof meet. As rainwater pours off the roof, it tends to collect and run down to the eaves along the valleys, so extra reinforcement is needed here to prevent water from seeping through the roof material. Flashing in usually laid down in a single, long sheet, with a bend in the middle to fit into the valley. There are several ways to lay down shingles along valley flashing, which either covers up the flashing or leaves a clean edge where the flashing is visible
Vent Pipe Flashing
This type of flashing is installed around the base of a vent pipe, which can be another point of vulnerability on a rooftop.
What Happens if Roof Flashing Fails
If roof flashing fails due to rust, damage, or improper installation, water can penetrate beneath the flashing and roofing materials and permeate the interior structure of the building. Eventually, the water will make its way through and cause leaks, rot, sheetrock damage, or even structural issues.
Keep an eye out for signs of damage including rust, cracking, missing or loose panels, missing screws or nails, and lifting. If you notice any of these signs, it may be indicative of deeper damage to your shingles and roof. Call Golden City Remodeling at (310) 361-3271 if you need replacement or repair for your roof flashing or shingles!