Flashing on a Roof in Prescott: Where Roofs Actually Leak

A homeowner cannot see flashing fail. It is behind the shingles, behind the siding and above the ceiling, and by the time it announces itself the announcement is a stain, a soft spot in a wall, or a bill with the word "sheathing" in it.

Which is why most of what gets sold as a roof leak is not a hole in anything. It is a flashing detail that was never right.

Roof flashing types, and what each one does

Flashing is thin metal at the joints. Shingles handle open slope; flashing handles everywhere it stops.

Detail	Where it lives	How it fails
Step flashing	Slope running up beside a wall	One long strip instead; reused on a tear-off
Apron / headwall	Slope dead-ending into a wall	Too short, or buried behind siding
Kickout	Bottom of a sidewall run	Simply absent
Valley	Where two slopes meet	Corroded at the crease, or debris-dammed
Chimney base and counter	Four faces of a chimney	Caulked to the face, not let into the mortar
Drip edge	Eaves and rakes	Missing, so water wraps onto the fascia

Every row is a place where a fast crew can do something that looks finished from the driveway.

Step flashing: one piece per course, or it is something else

Step flashing is individual L-shaped squares of metal, one per shingle course, each lapping the one below. Water hitting any piece is handed to the next, and the last one hands it to the roof. Nothing depends on sealant; it works because of the order things went on in.

The substitution to know about is continuous flashing: one long bent strip run up the wall in a single length. It goes on in a fraction of the time, it looks correct from a ladder, and it has nothing to shed water that gets behind its top edge but the caulk somebody ran along it.

The part that catches people out: the residential code permits either. R905.2.8.3 says base flashing against a vertical sidewall "shall be continuous or step flashing," at least four inches high and four inches wide, directing water onto the roof or into the gutter. Shingle manufacturers are the ones who insist on one piece per course, and code makes their instructions binding by a separate route.

Roof to wall flashing: headwall and sidewall are different problems

Roof to wall flashing is two details rather than one, and they fail differently.

Sidewall is where the slope runs up beside the wall — a dormer cheek, a garage meeting the house side-on. Step flashing territory, one piece per course, all the way up.

Headwall is where the slope runs into a wall and stops — a porch or an addition roof dying into the second story. That takes apron flashing: one continuous piece, up the wall behind the cladding and out over the shingles. The failure is termination — cladding brought down tight with no clearance, so the siding wicks and the flashing has nowhere to drain.

Kickout flashing, and the wall it saves

A kickout is the first step flashing at the bottom of the wall, bent outward to throw water clear of the cladding and into the gutter. A dormer cheek in a storm is a funnel, collecting the runoff of everything above it and delivering it to one point a few inches wide. With a kickout, that water lands in the gutter. Without one, it goes behind the siding, into the sheathing, and down inside the wall.

This failure does not look like a roof problem. There is no ceiling stain, because the water never gets inside the roof. It shows up years later as peeling paint below a dormer, a soft spot in the sheathing, or a trim board that will not hold a nail. The Department of Energy's Building America guidance is blunt: missing kickout and step flashing has cost homeowners thousands, and vinyl or fiber-cement siding hides it until the sheathing is gone.

The part costs almost nothing. The wall repair does not.

Counter-flashing: a reglet, or caulk with a countdown

At a chimney or any masonry wall, flashing comes in two layers. Base flashing goes up the masonry from the roof side; counter-flashing comes down over the top of it, so water running down the wall lands outside the base flashing rather than behind it. How it attaches is the whole question:

• Let into a reglet — a groove raked into a mortar joint, the metal bent in, wedged, then sealed. The joint is the hold; sealant is secondary.
• Surface-mounted — held flat to the face with fasteners and a bead of caulk along the top. The sealant is the only thing keeping water out.

Nothing prohibits surface-mounting. But IIBEC calls it the most common defect at a brick chimney and says the caulk-dependent detail holds up only in light or short rain. Reglet depth is guidance rather than code, and the guidance disagrees: IIBEC's minimum is an inch, an inch and a half preferred; NRCA's Professional Roofing wants one and three-quarters to two and a half.

Reused step flashing: the cut nobody can see

On a tear-off, step flashing comes off with the shingles it is woven into. Removing it bends it, and bending aluminum or galvanized steel twice work-hardens it. The old nail holes no longer line up with the new courses. And the metal has been in weather exactly as long as the shingles that just failed.

So it gets reused — hammered flat, re-nailed, buried where nobody will look for fifteen years. Be fair about it: inspectors will tell you sound step flashing can be reintegrated with new courses, and on a young roof that is sometimes true. The problem is that the decision gets made in silence. The kickout goes the same way for a related reason — retrofitting one means opening the siding to weave the flashing in behind the weather barrier, which is exactly why, as Mike Guertin has written in JLC, kickouts get skipped on replacement work.

The defense is one line in the contract: new step flashing, new kickout flashing, new pipe boots, itemized. A crew that means to reuse the old metal will say so when you ask for it in writing, which is the useful part.

What is code, and what is trade practice

Code. IRC R903.2 requires flashing installed so moisture cannot enter the wall or roof at joints and penetrations. R903.2.1 lists where — wall and roof intersections, any change in roof slope or direction, around roof openings — and fixes the metal at corrosion-resistant, not less than 0.019 inch, No. 26 galvanized sheet. Asphalt shingles get their own set at R905.2.8, sidewall flashing at .3 and drip edge at .5, the drip edge only since the 2012 edition.

The kickout is the interesting one, because the code has never once called it a kickout. It arrived in the 2009 IRC inside the sidewall section, as an instruction to turn the step flashing out at the bottom, and in 2012 moved up to R903.2.1 as one sentence covering every roof covering: a flashing shall divert water away from where the eave of a sloped roof meets a vertical sidewall. No dimension, then or now. Minnesota's amendment names the part and sets a two-and-a-half-inch minimum — Minnesota, not the IRC.

Manufacturer instruction, made enforceable. R904.1 and R905.1 require roof assemblies and coverings to be applied per the manufacturer's installation instructions. That is the hook. "One piece of step flashing per shingle course" appears in no code text — it comes from the shingle maker, and those two sections give it teeth.

Trade practice. Reglet depth, kickout projection, valley lap: sheet metal convention, not code numbers. And your jurisdiction adopts an edition then amends it, so your inspector is the authority here, not any national text.

Who Arizona lets do this work

Flashing sits awkwardly in contractor law. A repair to one wall is often small enough to fall under whatever threshold the state wrote with full re-roofs in mind, which means the work most likely to be done wrong is the work least likely to be looked at.

Look for R-42, the residential roofing classification at the Registrar of Contractors; C-42 is the commercial version and CR-42 covers both. The thousand-dollar handyman exemption will not help anyone reroofing your house, and the reason is the dollar limit rather than the permit trigger: the exemption also requires that no permit be needed, and since 15 September 2025 a like-material reroof in unincorporated Mohave County needs none, so there the exemption survives right up to its thousand dollars - which still does not buy a roof. An unlicensed contractor cannot maintain a collection action in any Arizona court, and that bar is applied even to work outside the classification actually held.

Worth knowing before you find out from the inside of a wall.

How to check without getting on the roof

Stand under every place a wall meets a roof — dormer cheeks, a garage roof into the house, a porch into the second story — and look at the bottom corner.

• A kickout is a small tab of metal turning out above the gutter. Siding running straight down to the roof with nothing turned out means there is not one.
• Peeling paint or a dark streak below that joint is the wall telling you where the water went.
• A caulk line across a chimney with no metal let into the mortar is maintenance pretending to be a detail.
• Sheathing that gives when you push the wall below the joint is a carpentry problem now, not a roofing one.

Past that you need somebody on the roof, and a written roof inspection with photographs beats a verbal opinion, because flashing arguments are always about what is underneath something. If you already have a live leak, tracing it to the entry point comes first — its own process, covered in how to find and fix a roof leak.

Bottom line

Flashing is where roofs leak, and it is the part you are least equipped to inspect and least likely to be shown. Ask for step flashing one piece per course, a kickout at the bottom of every sidewall, counter-flashing let into the mortar rather than caulked to the face, and new metal rather than reused. Name all four in the contract, because the day the shingles go on is the last day any of it is visible.

Those four details are worth naming in the contract, because once the shingles are on nobody can check them. Prescott Roof Pros does flashing detail work — step, kickout, counter-flashing, valley metal — on repairs and on full roof replacement in Prescott and Arizona's Central Highlands, and photographs all of it in every roof inspection we write. Call (877) 834-9598 and have someone look at yours while it is still visible.