Kickout Flashing: The Small Part That Stops Wall Rot

Every place a roof slope ends against a vertical wall is a place where water has to make a choice: drop into the gutter below, or keep going straight down the face of the wall instead. Most of that roof-to-wall run is protected by step flashing, the overlapping metal pieces woven in with each course of siding as the roof climbs the wall. Step flashing does its job while the water is still running downhill along the wall. But at the very bottom, right where the roof plane ends and the gutter begins, the water needs one more instruction, and step flashing alone does not give it. The piece that does is called kickout flashing, one of the smallest and cheapest details on an entire roof. It is also one of the most commonly left out, and a missing kickout is a quiet way to rot a wall from the inside for years before a homeowner sees anything at all.

01 / THE SHORT ANSWERWhat kickout flashing does, in one sentence

Kickout flashing is a short, diagonal piece of metal installed at the bottom termination of a roof-to-wall step flashing run, and its only job is to divert the water sheeting down that wall out and away from the siding, into the gutter below instead of behind it. It is sometimes called diverter flashing or kick flashing, and it looks unremarkable, a small bent scrap tucked into a corner most people never look at closely. But that scrap is the difference between water that lands in a gutter and water that lands inside a wall.

This is a detail problem, not a material problem. A roof can have excellent shingles, sound step flashing, and a clean gutter, and still funnel water into the wall for a decade if this one part was never installed. It is also one of the details a roofer working only on the roof surface can miss entirely, because the kickout lives at the boundary between roofing work and siding work, and on too many houses neither trade claimed it.

02 / THE LOCATIONWhere this detail lives on your house

Look for it anywhere a lower roof plane runs into a taller wall: a porch roof tucked under a two-story wall, a garage roof meeting the side of the house, a dormer, an addition, or a bay window with its own little roof. In each case the roof's sloped edge is stitched to the wall with step flashing, one L-shaped piece per shingle course, each one lapped over the piece below it so water is always shed outward and downward, course after course, all the way up the slope.

At the bottom of that run, the roof plane stops and a gutter usually starts right at the same corner. The last piece of step flashing in the run cannot simply end at the wall, because everything that ran down the whole length of that step flashing run arrives at that one corner in a concentrated stream. Without something to turn it, that stream keeps doing what step flashing taught it to do for the entire run above: hug the wall and keep going down, straight behind the siding and past the end of the gutter instead of into it. Kickout flashing is the piece that breaks that habit at the one point where it matters most, angling out from the wall to physically push the water into the trough.

Macomb County has plenty of house shapes that create this corner. A ranch with a later garage addition, a split level with a porch roof tucked under the upper story, a colonial with a bay window or dormer, and a bungalow with a side entry roof all have at least one, and often several, of these roof-to-wall intersections. Each one was built or re-sided at a different time, sometimes by a different crew, which is exactly why a house can have this detail done right at the front porch and skipped entirely at a side addition put on twenty years later.

03 / THE DAMAGEWhat happens when it's missing

A missing kickout rarely announces itself. There is no leak inside the house on day one, no dramatic stain on a ceiling, nothing that sends anyone up a ladder to investigate. What happens instead is slow. Every rain sends a stream of water behind the bottom edge of the siding at that corner, where it soaks the housewrap or building paper, finds the staples and seams, and works its way to the wood sheathing underneath. Wood that stays damp for years does not rot in a season. It rots the way most serious roof problems do, one storm at a time, invisibly, until the damage is structural rather than cosmetic.

A leak from the roof surface usually shows up inside the house within a season. A missing kickout can rot a wall for years and never show up anywhere but outside, at that one corner, if you know to look.

By the time this kind of damage becomes visible, it is often further along than it looks. Siding hides the sheathing behind it, so a homeowner sees a faint stain or a slightly soft spot on the exterior long after the framing behind it has already been wet for years. Because this is gradual water intrusion rather than a sudden storm event, it generally falls outside what a homeowners insurance policy covers, which typically responds to sudden wind and hail damage rather than years of slow seepage from a missing detail. That makes catching it early, before it becomes a sheathing and framing repair, worth real money.

04 / SPOT IT YOURSELFReading your own house for the signs

You do not need to get on a roof to check for this. Walk the outside of your house and look specifically at every spot where a lower roof plane dies into a taller wall, then look just below that corner, at the siding right above where the gutter ends. That one corner, on every such intersection on your house, is where the evidence collects.

• A dark vertical stain or streak on the siding directly below the corner where the roof meets the wall, often shaped like a narrow stripe rather than a wide splash.
• Paint that is bubbling, peeling, or discolored at that specific corner and nowhere else nearby on the same wall.
• Siding that feels soft, looks slightly warped, or has separated at the seams right at that intersection.
• A gap you can see between the end of the gutter and the wall, with no small diagonal metal piece tucked into that corner.
• Green algae, moss, or a chalky white mineral streak on the siding just below the joint, a sign water has been running there long enough to leave residue.

Check every roof-to-wall intersection on the house this way, not just one. A house can have this detail done correctly on the front porch roof and missing on a side addition, because it is often installed inconsistently by whoever built or re-sided that section over the years. If you see any of these signs at more than one corner, that is a pattern worth having looked at rather than a coincidence.

05 / THE RETROFITWhat the fix actually involves

Adding a kickout where one was never installed is a retrofit, not a full reroof, but it is more involved than caulking the corner, and it should be. Caulk is not a substitute for a diverter; it slows the problem down and then fails, usually at the worst possible time. A proper fix opens the detail up and rebuilds it correctly.

1. Siding comes loose at the corner. A course or two of siding near the intersection is carefully pulled back or removed so the bottom of the step flashing run is exposed.
2. The kickout piece is fabricated and set. It is bent to the specific angle of that roof pitch and wall, then woven in behind the last piece of step flashing and over the top of the gutter's end, so it inherits the water the step flashing has been carrying the whole way down.
3. The gutter end is adjusted. Sometimes the gutter's end cap needs to be trimmed or repositioned slightly so the diverted water actually lands inside the trough instead of clipping the outside edge of it.
4. Siding goes back over the repair, restoring the weather barrier and hiding the metal the way it is supposed to be hidden: doing its job in a corner nobody looks at twice.
5. The sheathing gets a look. Whenever this corner is opened up, it is the moment to check the wall sheathing behind it for the softness or rot the missing kickout may have already caused. If it is sound, the retrofit closes the case. If it is not, that repair gets scoped honestly before the siding closes back over it.

06 / THE COSTCost, timing, and getting it fixed

A kickout retrofit is not its own separate price line in our published canon; it is priced as a repair, and Macomb County roof repairs generally run $350 to $3,200 depending on scope. A single corner with sound sheathing behind it lands toward the low end. A corner where the sheathing has to be replaced, or where the siding is old enough that matching it is its own job, pushes higher. Larger or more complex repairs can run above that range, which is exactly why a written price after a free inspection matters more than a guess over the phone.

This detail also has a habit of surfacing during other work rather than on its own. It is frequently found and corrected during a roof repair visit for something unrelated, during a full reroof when the flashing at every wall intersection gets reset anyway, or during a siding project, when the corner is already open for other reasons. If you already have roof work planned, mentioning any staining you have noticed at a wall corner is worth a sentence on the phone, because it directs the inspection to look at that spot specifically rather than finding it by accident later. Our repair estimator and cost calculator use the same published ranges as our honest pricing sheet, and a kickout retrofit is scoped the same honest way: photos of the corner, a written price, and no obligation to move forward.

Timing matters here more than it does for a lot of repairs, because the damage keeps compounding quietly for as long as the detail is missing. A corner caught early might need nothing more than the metal itself and a course of siding put back. A corner left for years can mean sheathing, and occasionally framing, has to come out along with it. Neither problem gets smaller by waiting through another Macomb County winter, and the inspection that tells you which one you actually have costs nothing.

If you are also dealing with related edge problems, our guides on rotted fascia boards and gutters overflowing in heavy rain cover the neighboring failures that often show up on the same house, and our explainer on chimney flashing covers the other roof-to-vertical-surface detail that fails for very similar reasons. The full library of roof-edge and flashing guides lives in our guides section.