Ask any experienced roofer in the Chicago area where most leaks actually start, and you’ll rarely hear “the shingles.” The honest answer is almost always the same: flashing. Those thin strips of metal tucked around chimneys, skylights, walls, and valleys account for a disproportionate share of the leaks our crews at All Roofs Inc. are called out to fix – and most homeowners have never given them a second thought.
This guide explains what roof flashing is, every place it’s installed on a typical home, the materials roofers use, and – most importantly – why it fails and how to recognize the warning signs before water reaches your ceilings.
What Is Roof Flashing?
Roof flashing is a thin, water-resistant material – usually metal – installed wherever the roof surface is interrupted or meets another surface. Shingles are excellent at shedding water on a flat, continuous plane, but they cannot seal a joint. Every time a roof changes direction, meets a wall, or has something poking through it (a chimney, a vent pipe, a skylight), there is a gap that shingles alone cannot protect.
Flashing bridges that gap. It directs water away from the joint and back onto the shingles, where gravity carries it down to the gutters. Think of it as the roof’s plumbing: invisible when it works, and the first thing you notice when it doesn’t.
Well-installed flashing is layered into the roofing system in a specific order – under some materials, over others – so that water never has a chance to travel upward or sideways into the structure. That layering is exactly why flashing is so unforgiving of mistakes: a strip installed in the wrong sequence looks fine from the ground and leaks the first time it rains sideways.
Where Flashing Goes on a Roof
Walk around a typical Chicagoland home and you’ll find flashing in at least six distinct places. Each has its own name, shape, and installation method.
1. Chimney flashing
The chimney is the single most leak-prone spot on most roofs, and it uses the most complex flashing assembly. A proper chimney flashing system has several parts working together:
- Base flashing at the bottom of the chimney where it meets the roof deck.
- Step flashing – individual L-shaped pieces woven into each course of shingles along the sides.
- Counter flashing (also called cap flashing) – embedded into the mortar joints of the chimney and folded down over the step flashing to seal the top edge.
- Cricket or saddle – a small peaked structure behind wider chimneys that splits water flow so it doesn’t pool against the back wall.
When any one of these layers is missing, corroded, or improperly sealed, water finds its way behind the brick and into the attic. Missing crickets and counter flashing that’s been caulked to the brick surface instead of let into the mortar are two of the most common defects we find on older Chicago homes.
2. Step flashing (roof-to-wall)
Wherever a sloped roof runs alongside a vertical wall – a second-story wall above a garage roof, a dormer side, a split-level – roofers install step flashing. Each piece is bent at 90 degrees, with one leg lying on the roof under a shingle and the other running up the wall behind the siding or housewrap. The pieces overlap like shingles, “stepping” up the slope.
Step flashing done correctly is nearly bulletproof. Step flashing done as one long continuous strip (a shortcut still seen on some jobs) will eventually leak because it can’t move with the roof.
3. Valley flashing
A valley is the internal angle where two roof planes meet, and it carries more concentrated water than any other part of the roof. In a heavy Midwest thunderstorm, a valley can be moving several gallons per minute. Depending on the roof, roofers use:
- Open metal valleys – a wide, visible strip of metal (often pre-formed with a center rib) with shingles trimmed back on either side.
- Closed-cut valleys – shingles from one slope run through the valley and the other side is cut cleanly along a line, with ice-and-water membrane underneath.
- Woven valleys – shingles interlaced across the valley (less common with modern heavier architectural shingles).
Because valleys also collect leaves, granules, and – in our climate – ice, they wear out faster than surrounding shingles and are a frequent source of leaks on roofs that otherwise look healthy.
4. Pipe boots and vent flashing
Every plumbing vent, exhaust fan duct, and furnace vent that pokes through the roof needs its own flashing. For plumbing stacks, that’s usually a pipe boot: a metal or plastic base plate with a rubber (neoprene) collar that seals around the pipe.
The rubber collar is the weak link. After 10–15 years of Illinois sun, freezing, and thawing, the rubber cracks and splits. A cracked pipe boot is one of the most common causes of the mystery ceiling stain that “only shows up after a big storm.”
5. Skylight flashing
Skylights use a manufacturer-specific kit that combines sill flashing at the bottom, step flashing up the sides, and head (or saddle) flashing across the top. Skylights installed without the proper kit – or with “universal” flashing improvised on site – are a recurring source of leaks. If you have a skylight, our guide on how to maintain a skylight covers what to watch for.
6. Drip edge and eave flashing
Drip edge is the L-shaped metal along the edges of the roof. It’s technically a form of flashing, and it plays a major role in keeping water out of the fascia and off the roof deck edge. It’s important enough to deserve its own article – see our guide to drip edge.
7. Kick-out flashing
A small but critical piece: kick-out flashing sits at the bottom of a roof-to-wall intersection and “kicks” water out into the gutter instead of letting it run down behind the siding. Missing kick-out flashing is a classic cause of rotted wall sheathing and mold inside exterior walls – damage that often isn’t discovered until the siding comes off.
Roof Flashing Materials
Not all flashing is created equal, and the material a roofer chooses affects how long it lasts in a freeze-thaw climate like ours.
| Material | Typical lifespan | Notes |
| Galvanized steel | 15–25 years | Most common; affordable; can rust once the zinc coating wears |
| Aluminum | 20–30 years | Lightweight, corrosion-resistant; must not contact masonry/concrete directly (reacts with alkalis) |
| Copper | 50+ years | Premium; develops a protective patina; the standard for high-end chimney work |
| Lead | 50+ years | Extremely malleable; traditional for chimneys, less common today |
| Rubber / neoprene | 10–15 years | Used in pipe boots; the first component to fail |
| Peel-and-stick membrane | Varies | Used as a secondary layer beneath metal flashing, not a replacement for it |
A good roofing contractor will also match the flashing to the roof. Metal roofs, for example, require flashing and closures designed for the specific panel profile. You can read more about that on our metal roofing page.
Why Roof Flashing Fails
Flashing rarely fails all at once. It degrades, shifts, or was never right to begin with. The causes we see most often on Chicago-area roofs:
Corrosion. Galvanized steel eventually rusts, especially in valleys and around chimneys where water sits longer. Once rust perforates the metal, it leaks.
Thermal movement. Metal expands in July heat and contracts in January cold. Over decades, this movement loosens fasteners, opens seams, and pulls sealant away from the metal.
Sealant failure. Caulk and roofing cement are meant to be a secondary line of defense, not the primary seal. Flashing that relies on caulk alone will leak as soon as the caulk dries out and cracks – typically within a few years.
Ice dams. When ice builds up at the eaves and in valleys, meltwater is forced upward under shingles and flashing – the opposite direction the system was designed for. Homes without proper ice-and-water membrane behind their flashing are especially vulnerable. Our ice dam removal service exists largely because of this.
Wind and hail. Severe storms can lift, bend, or dent flashing. Hail that leaves visible dents in soft metal is also a signal to check the shingles – see how hail damages your roof.
Poor installation. This is the big one. Flashing installed in the wrong sequence, step flashing replaced with a continuous strip, counter flashing surface-caulked instead of embedded in mortar, missing crickets, missing kick-outs – these are not wear issues. They’re defects that will leak no matter how new the roof is.
Previous “quick fixes.” Layers of roofing tar smeared over a leaking joint are a red flag on any inspection. Tar hides the problem, traps moisture, and makes a proper repair harder later.
Signs Your Flashing Is Failing
You don’t need to climb on the roof to spot the early warnings. From the ground and the attic, look for:
- Water stains on ceilings or walls near a chimney, skylight, or exterior wall – leaks that follow a joint rather than appearing in the middle of a room.
- Rust streaks or discoloration on visible flashing or on the siding just below a roof-to-wall joint.
- Lifted, bent, or missing metal around the chimney or along walls.
- Cracked, dried, or missing sealant where flashing meets brick or siding.
- Moisture, dark staining, or daylight in the attic around penetrations.
- Damp or crumbling mortar on the chimney at the roofline.
- Peeling paint or bubbling on interior walls below a dormer or where a lower roof meets an upper wall.
- Leaks that only appear during wind-driven rain – a classic flashing symptom, since flashing is what protects joints from sideways water.
Not every ceiling stain is flashing, of course. Our article Why Is My Roof Leaking? walks through the other common causes.
Why Flashing Isn’t a Do-It-Yourself Job
It’s tempting to look at a small strip of metal and think a tube of caulk will solve it. In practice, flashing work is one of the most technically demanding parts of roofing:
- Sequence matters more than material. Each piece has to be layered correctly with the shingles, underlayment, and ice-and-water membrane beneath it. Getting one overlap backward guarantees a leak.
- The problem is usually hidden. By the time water shows up inside, the damaged flashing is under shingles, behind siding, or embedded in mortar. Diagnosing the true entry point takes experience.
- Caulk is not a repair. Surface-sealing a flashing joint buys months at most and usually makes the eventual professional repair more expensive.
- Chimneys and skylights require masonry and carpentry skills, not just roofing.
- Fall risk. Flashing lives at the most awkward places on the roof – valleys, walls, and steep areas around chimneys.
A professional roofer will identify whether the flashing can be resealed, whether individual pieces need replacement, or whether the roof around it has been damaged enough to need a larger repair. That judgment is where the money is saved.
How All Roofs Inc. Handles Flashing Repairs
For over 30 years, All Roofs Inc. has been repairing and replacing flashing on homes and commercial buildings across Chicago and the surrounding suburbs. Our approach:
- Thorough inspection – on the roof and in the attic, tracing the leak to its true source rather than the spot where water appears.
- Honest recommendation – if a targeted roof repair will solve the problem, that’s what we recommend. If the flashing failure is a symptom of a roof that’s reached the end of its life, we’ll explain why and discuss roof replacement options.
- Proper materials and sequencing – new flashing is integrated with ice-and-water membrane and installed in the correct layering order. Chimney counter flashing goes into the mortar joint, not on top of the brick.
- Storm-damage support – if the flashing was damaged by wind, hail, or ice, our in-house public adjuster assistance helps you document the damage and work with your insurance company. See also: Is roof repair covered by insurance?
- 24/7 emergency response – active leaks don’t wait for business hours. Our emergency roofing team can stop the water and protect your home until the permanent repair is scheduled.
Frequently Asked Questions About Roof Flashing
How long does roof flashing last? It depends on the material and location. Galvanized steel typically lasts 15–25 years, aluminum 20–30, and copper 50 or more. Rubber pipe boots often fail in 10–15 years. Flashing should be evaluated at every roof inspection.
Should flashing be replaced when the roof is replaced? In most cases, yes. Reusing old flashing on a new roof is a common cost-cutting shortcut that leads to leaks within a few years. At All Roofs Inc., new flashing is part of a standard roof installation.
Can flashing be repaired without replacing the shingles around it? Often, yes. Skilled roofers can lift and reset surrounding shingles to replace step flashing or a pipe boot. Whether that’s the right call depends on the age and condition of the shingles – another reason a professional inspection comes first.
My chimney flashing is leaking. Is that a roofer’s job or a mason’s? Usually both skills are needed, which is why chimney leaks are so often fixed incorrectly. A roofing contractor experienced with chimney flashing will handle the step flashing, cricket, and shingle integration, and will either cut new counter flashing into the mortar or coordinate with masonry repair if the chimney itself is deteriorating.
Is a leak near my chimney always the flashing? Not always. Cracked chimney crowns, deteriorated mortar, and missing chimney caps can all let water in. A proper inspection distinguishes between them.
Don’t Wait for the Stain to Spread
Flashing problems are small until they aren’t. A minor leak at a chimney can quietly rot roof decking, soak insulation, and grow mold for months before the ceiling shows it. Catching it early is the difference between a straightforward repair and a much larger project.
If you’ve noticed staining near a chimney or wall, rust on your flashing, or leaks that appear only in wind-driven rain, contact All Roofs Inc. or call (866) 205-8833 for a free inspection and estimate. We serve homeowners and businesses throughout Chicago and the surrounding suburbs, and we’ll tell you honestly what your roof needs.
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