Flashing Is Where Roofs Actually Leak

September 2026

Nobody calls us because the middle of their roof failed

Think about every leak you have ever heard about. The stain was near a chimney, or under a skylight, or in the corner of a room where a second story wall comes down onto a garage roof, or in a hallway ceiling below a bathroom vent. It was never in the middle of a wide open slope with nothing around it.

That is not luck. Shingles in the field do one simple thing, they overlap and shed water downhill, and they are very good at it. Every hard part of a roof is a transition: where the plane changes direction, where something pokes through, where the roof meets a wall. Those get handled by metal, the metal is called flashing, and flashing is where roofs actually leak.

What flashing is doing

Flashing is sheet metal shaped and layered so water hits it and gets steered back onto the shingles below. It is not a seal and it does not depend on sticking to anything. A correct detail works on geometry and overlap, the way a shingle does, and if you took every drop of sealant off a properly flashed chimney it would still be dry.

That distinction explains almost every failure in this article. Flash with caulk instead of metal and you have built something that works until the caulk fails, and caulk always fails. Sealant is a consumable: flexible for a handful of years at this elevation, then it shrinks, crazes and pulls away from one edge. If the sealant was the waterproofing, you now have a leak.

Metal keeps water out. Sealant buys the metal a little insurance. Anything relying on the sealant is a repair waiting to happen.

The transitions, and how each one fails

Where a roof meets a wall

This is step flashing, the detail most often done wrong on houses in this valley. It should be individual L-shaped pieces, one per shingle course, each tucked under the course above it and up behind the wall covering, so water running down the wall steps its way down onto the shingles.

What we find instead is one long strip of bent metal laid in the corner and caulked along the top edge. It looks tidy. There is no lap anywhere, so water behind that top edge has a continuous path the whole length. One strip is the most reliable sign the roof was done fast.

The other half is counterflashing, or on a sided wall, the siding lapping over the step flashing. The vertical leg has to go up behind something. Metal that stops at the siding line and gets caulked to its face is a leak with a schedule.

Chimneys

A masonry chimney is the hardest thing on a roof and it is where we do the most repair work. It needs four separate pieces done right: a base flashing across the downhill face, step flashing up both sides, counterflashing cut into a mortar joint and sealed there, and on any chimney more than about thirty inches wide, a cricket on the uphill side.

The cricket is the one that gets skipped. It is a small peaked structure behind the chimney that splits water and snow and sends it around either side. Without one the uphill face is a dam, and everything on that slope arrives and sits there. On a wide chimney with no cricket it leaks eventually.

Counterflashing is the other one. Done properly, a slot gets cut into the mortar joint and the metal is sealed in the slot. The fast version, surface mount, sets the metal against the face of the brick with a bead of sealant along the top. That bead is now the only thing keeping water out of the wall, and it sits in full sun.

Valleys

A valley is where two slopes meet and everything from both of them runs into one channel. It carries more water than any other part of your roof, and it does it at speed.

Two legitimate ways to build one. An open valley runs a wide piece of metal down the center with the shingles stopping short on both sides. A closed valley weaves or cuts the shingles across it over membrane and metal. Both work. Open valleys handle volume and debris better, which suits the pine and cottonwood cover on the bench lots.

Valleys fail underneath. The metal rusts from the bottom third up, where water sits longest and debris packs in wet. Tear off a roof with old valley metal reused under newer shingles and it is usually gone at the bottom. The other failure is a nail driven through the metal inside the water channel, putting a hole in the one part of the roof carrying concentrated flow.

Pipe collars

The shortest-lived thing on most roofs and the most common single cause of a ceiling stain. A plumbing vent comes through the deck and gets a flashing with a rubber collar sealing around the pipe. Ultraviolet at this elevation destroys that rubber, it cracks in a ring somewhere between eight and fifteen years, and the crack sits directly over an open hole through your deck.

The good news is that it is cheap and quick, and the better fix is a collar with a metal storm collar or a lead sleeve rather than bare rubber. If your roof is over ten years old, that is the first place to look.

Skylights

Skylights get blamed for leaks that are flashing failures around them. A modern curb-mounted unit comes with an engineered kit cut for its own dimensions, and installed per that kit it is dry for decades. Installed with generic metal and sealant, it leaks.

The uphill side has the same problem a chimney does: water and snow arrive and have to go around, which on a wide skylight on a shallow slope needs real thought rather than caulk. The glazing seal has its own lifespan too, so a twenty-five year old skylight that weeps may be the unit. Replace it while the roof is off.

Drip edge and the rake

Drip edge is the L-shaped metal along the eaves and rakes. It keeps water from wicking back under the shingle edge into the fascia and gives a wind-driven edge something to hold. Plenty of older roofs here have none, and the evidence is a fascia board soft along the top with paint that will not hold.

The sequence matters. At the eave, drip edge goes under the underlayment. At the rake, it goes over. Get that backward and the metal channels water into the deck edge instead of away from it.

How to read your own roof for flashing trouble

You can learn a fair amount from the ground with binoculars and from the attic with a flashlight.

• Look for caulk. Any thick smeared bead you can see is a place somebody solved a flashing problem the fast way. Fresh caulk on an old roof means a previous repair.
• Look at chimney sides. Individual stepped pieces of metal, or one long strip? One strip is a flag.
• Look behind the chimney. Is there a small peak, or does the slope run straight into the brick?
• Look at valley bottoms. Rust staining, packed debris, or shingle edges crumbled back.
• In the attic, follow the stain up. Water travels along rafters and the underside of the deck before it drops, sometimes several feet. The wet spot on your drywall is almost never below the hole. The entry point is uphill of it.

Why flashing gets reused, and why we do not

On a re-roof, pulling and replacing all the metal costs material and time, and both show up in the number. Leaving it and running new shingles over the top saves a crew half a day on a complicated house.

So it happens, and it is the most common reason a roof only twelve or fifteen years old is leaking. The shingles are fine. The metal under them was already halfway through its life when it got covered.

We pull it. Step flashing, valley metal, pipe collars, chimney counterflashing and the base pan come off with the old roof and new goes in. The exception we will talk through is heavy custom metal in genuinely good shape, and that is a conversation rather than a decision we make quietly on the roof.

A leak is not automatically a new roof

Worth saying plainly, because it is a large share of the calls we take. A cracked pipe collar is a short job. Step flashing redone along one wall is a short job. A cricket behind a chimney that never had one is a day. We do those and say so, because a shop that answers every leak with a replacement quote runs out of neighbors to work for.

If you have a stain and you want somebody to find where the water is actually getting in, call (801) 382-8898 or reach us on the contact page.

Questions we get about flashing and leaks

My roofer wants to just caulk the chimney. Is that ever the right answer?

As a temporary measure before a proper repair, sometimes, and it should be described that way. As the repair itself, no. Sealant on the face of masonry is exposed to full sun and it will pull away from one edge within a few years. The real fix is counterflashing cut into a mortar joint, and it is not an enormous job.

Water only comes in during wind-driven rain. What does that mean?

Usually a wall or a sidewall flashing detail rather than a hole in the field. Water arriving horizontally gets behind things that handle water coming straight down perfectly well. Check where a wall meets the roof, the tops of step flashing runs, and any place siding laps over metal.

The stain in my ceiling is nowhere near the chimney. Can the chimney still be the source?

Easily. Water that gets through at a penetration runs along the underside of the sheathing or down a rafter until it hits something that stops it, then drops. We have traced stains eight or ten feet from the entry point. Finding the source means getting in the attic and working uphill from the wet spot.

How long should flashing last?

Galvanized steel gives you a couple of decades, less at a valley bottom where it stays wet. Aluminum lasts well but is soft and dents. Copper outlives everything on the house and costs accordingly. The practical answer is that flashing and shingles are roughly on the same clock, which is exactly why they should be replaced together.

Is a leak around a bathroom vent a flashing problem or a ventilation problem?

Check both. A roof cap flashed poorly leaks. A bath fan ducted into the attic instead of out through a cap puts moist air against cold sheathing all winter, and the condensation that drips back down gets mistaken for a leak. The tell is timing: a real leak shows up with weather, condensation shows up in cold weather regardless of rain.

The unglamorous half of a roof

Nobody picks a roofer based on their step flashing. It is not visible from the street and it does not show up in a photograph of a finished job. It is also, along with the ventilation and the decking, the part that decides whether you are calling somebody in four years.

We are a family shop out of Salt Lake City, second generation, twenty-seven years in the trade and eight under the Hancock Signature name. If you want somebody to look at your transitions rather than quote you a field of shingles, call (801) 382-8898 or leave us a note on the contact form.