8 min read · Guide
If we could point to one missing part responsible for more hidden dry rot on California homes than any other, it would be kickout flashing — a single, inexpensive piece of bent metal at the spot where a roof edge dies into a wall. Without it, everything a roof slope collects in a winter storm pours down the wall face and, worse, behind the siding, concentrated into a strip a few inches wide. This guide covers what a kickout is, why its absence is so destructive, how to read the stain pattern on your own walls, what the code actually requires, and why a re-side is the moment to fix it permanently.
What kickout flashing is
A kickout — also called a diverter — is an L-shaped flashing installed at the lowest piece of step flashing, exactly where a sloped roof edge terminates against a vertical sidewall. Its job is mechanical and simple: catch the water running down the roof-wall joint and *kick it out* — away from the cladding and into the gutter — instead of letting it continue down the face of the wall or behind the siding. The DOE's building-science education material describes them as prefabricated molded pieces or metal with welded seams, sized to handle expected stormwater flow; InspectAPedia's kickout guide shows the placement and the failures. It costs a few dollars as a part. It's omitted constantly — because it sits at the seam between two trades (roofer and siding installer), because it's visible and some crews think it looks fussy, and because nothing bad happens on day one when it's missing.
How to spot the stain pattern from the ground
You can often diagnose a missing kickout from the sidewalk. Look at any spot where a roof edge (especially above a gutter end) meets a wall that continues past it, and check for: a **vertical stain or streak** starting at that corner and running down the siding — dirt tracks, algae green, or tannin brown; **paint peeling or blistering** in a column below the intersection; **soft, swollen, or discolored trim** at or below the corner; a gutter end cap that overflows or shows splash-out staining; and in stucco, a rusty or chalky wash-down streak below the roof termination. Indoors, the late-stage signs are a musty smell or drywall staining on the wall behind that corner. The pattern is distinctive precisely because the water source is a point, not a face: damage concentrated in a narrow band below one roof-wall corner, while the rest of the elevation looks healthy. If you see it, don't repaint over it — the stain is the symptom, and the sheathing behind it is the question. A siding inspection or an exploratory opening settles what a pressure wash would only hide.
What the code actually requires
This isn't just best practice — it's code, and has been in the model codes since 2009. The California Residential Code's roof-assembly chapter, R903.2.1, requires flashing at wall and roof intersections and states that 'a flashing shall be installed to divert the water away from where the eave of a sloped roof intersects a vertical sidewall' — that sentence *is* the kickout requirement, even though the code never uses the word. Its companion, R905.2.8.3, requires continuous or step base flashing against sidewalls, sized and installed to 'direct water away from the vertical sidewall onto the roof or into the gutter.' On the wall side, CRC R703.4 independently requires corrosion-resistant flashing at wall-roof intersections. So on any permitted reroof or re-side today, the diverter belongs in the job — but millions of California homes were built or reroofed before enforcement caught up, which is why the missing kickout is overwhelmingly an *existing-home* defect rather than a new-construction one.
The retrofit: fixing it during a re-side, and tying into the gutter
A kickout can sometimes be retrofitted from outside — the bottom course of siding and the lowest step flashing are opened up, the diverter is slipped in and lapped correctly, and the cladding is patched — and that's worth doing on an otherwise healthy wall. But the honest limitation: if the kickout has been missing for years, the question isn't the flashing, it's what the water already did. A re-side is the clean fix, because with the cladding off we can see the sheathing, cut out any dry rot, rebuild the weather-resistive barrier so the new diverter laps *over* the WRB below and *under* it above (sequence is everything in flashing), and set a kickout at every roof-wall termination on the house. The gutter tie-in matters too: the diverter must actually discharge into the gutter — a kickout that overshoots a missing or sagging gutter just relocates the problem to the foundation. We coordinate that as part of gutter and siding integration, and it's a standard checkpoint on every re-side we scope — ask for it by name in any bid you're comparing, and see whether the answer is specific.
Key takeaways
- Kickout (diverter) flashing is an L-shaped piece at the bottom of a roof-wall intersection that throws roof runoff into the gutter instead of down and behind the siding.
- Its absence concentrates an entire roof plane's runoff into a few inches of wall — producing deep, localized, hidden dry rot rather than visible damage.
- The telltale is a vertical stain, peeling column, or soft trim directly below one roof-wall corner while the rest of the wall looks fine.
- It's code: CRC R903.2.1 requires flashing 'to divert the water away from where the eave of a sloped roof intersects a vertical sidewall' — in model codes since 2009.
- Retrofits from outside are possible, but a re-side is the definitive fix: inspect sheathing, repair rot, re-lap the WRB, and set a kickout at every termination, discharging into the gutter.
FAQ
Quick Answers
It's a small L-shaped diverter installed at the lowest piece of step flashing, where a sloped roof edge terminates against a vertical wall — typically right above a gutter end. It catches the water running down the roof-wall joint and directs it into the gutter instead of letting it run down the wall face or behind the siding.
Yes. CRC R903.2.1 requires flashing at wall and roof intersections and specifically requires a flashing 'to divert the water away from where the eave of a sloped roof intersects a vertical sidewall' — which is the kickout, by function if not by name. The requirement entered the model codes in the 2009 cycle, so older homes very commonly lack it.
Look for the pattern: a vertical stain, algae streak, or peeling-paint column starting at a roof-wall corner, soft or swollen trim below it, or musty smell and drywall staining inside on that wall. Because the water enters behind the cladding, surface signs lag the damage — the only definitive answer is a moisture reading and, where it's elevated, a small exploratory opening to see the sheathing. Repainting over the streak treats the symptom and hides the evidence.
Often yes — the bottom siding course and lowest step flashing are opened, the diverter is integrated with the correct laps, and the cladding is patched. It's worth doing promptly on a healthy wall. But if the kickout has been missing for years, budget for the possibility that the sheathing behind that corner needs repair, and if a re-side is on the horizon anyway, that's the moment to do it properly across every roof-wall termination on the house.
Sources
Authoritative references
- California Residential Code R903.2.1 — flashing shall divert water where the eave of a sloped roof intersects a vertical sidewall (via UpCodes)
- InspectAPedia — Kickout / diverter flashing: purpose, placement & retrofit
- U.S. DOE Building Science Education — Kick-out flashing at roof-wall intersections
- California Residential Code R703.1.1 — water resistance & a means of draining water that penetrates the cladding (via UpCodes)
External links to government, code, and manufacturer sources. Sierra Siding is not affiliated with these organizations; references are provided for verification.