If there is one component that matters most after the shingles themselves, it is flashing. Flashing is responsible for waterproofing every transition, every joint, every place where the roof plane meets something else. And it is where the majority of roof leaks originate.
What flashing does
Anywhere water could potentially get behind or under the shingles, flashing creates a watertight seal. Shingles are great at shedding water on a flat plane, but where the roof meets a wall, wraps around a chimney, runs through a valley, or transitions between different planes, the shingles alone cannot seal the joint. That is the flashing's job.
Types of flashing
Step flashing. L-shaped pieces of metal woven between shingle courses where the roof meets a vertical wall. Each piece steps up one shingle course, creating a shingle-over-metal-over-shingle pattern that directs water away from the wall. This is one of the things that separates quality roofers from shortcuts.
Counter flashing. A second layer that covers the top edge of step flashing, typically at chimneys. It is set into the mortar joints or mounted to the chimney face and bends down over the step flashing below. This two-layer system prevents water from getting behind the step flashing.
Valley flashing. Metal or specialized membrane material installed in the valley where two roof planes meet. Valleys channel more water than any other part of the roof, so the flashing here takes a beating. Open metal valleys and closed-cut valleys are both common, each with advantages depending on the roof.
Drip edge. Technically a type of flashing that runs along the eaves and rakes to direct water away from the fascia and into the gutters. Covered in its own article because it is commonly skipped.
Pipe boot flashing. The rubber or lead collar that seals around plumbing vent pipes and other round penetrations. Also covered separately because it is the most common repair we do.
Why flashing fails
Improper installation. This is the number one reason. Flashing that is not integrated correctly with the shingles, not properly sealed, or not sized right will fail. The shingles look fine, but the flashing work is sloppy and it is where every leak starts.
Sealant degradation. Flashing relies on sealant at many points, and roofing sealant has a limited lifespan. Three to seven years of UV exposure and temperature cycling breaks it down. When the sealant fails, the flashing joint opens up.
Rust and corrosion. Galvanized steel flashing can rust over time, especially in areas where standing water or debris collects. Once rust eats through the metal, you have an open pathway for water.
Thermal movement. Metal expands and contracts with temperature changes. Over years of Utah's extreme temperature swings, flashing joints can work themselves loose as the metal moves against the surrounding materials.
What to look for from the ground
Look for flashing that is visibly pulled away from a wall or chimney. Look for rust stains running down from metal surfaces. Look for sealant that has cracked or separated. Any of these are worth having a professional evaluate.
During a replacement, all step flashing and valley flashing should be replaced new. Counter flashing at chimneys may be reused if it is in good condition, but it should be inspected and re-sealed at minimum. If your estimate does not mention flashing replacement, ask about it.
Worried about flashing on your roof? We inspect every flashing point during our free inspections. If something is failing, we will show you photos and explain your options. Contact us.
"His workers were polite, careful not to damage my gutters and landscape, and they worked for several weeks in the freezing weather and snow. The finished product is something I am proud of. There were no surprise supplemental charges, the final bill being precisely what the estimate was."Eric Clough DVM , Google Review