Kickout Flashing Explained How It Protects Roofs Walls and Prevents Leaks
A roof can shed thousands of gallons of water in a hard storm. Most of that water travels safely into gutters, but trouble starts where a roof edge runs into a wall. Without the right flashing, runoff can slide behind siding, soak wall sheathing, and create hidden damage long before anyone sees a stain indoors.
That small but important piece at this intersection is called kickout flashing. It is simple in shape, easy to overlook, and one of the most important details in a weather-tight roofing system.
What kickout flashing does
Kickout flashing is a small, angled flashing installed where a sloped roof meets a vertical wall, usually at the lower end of a roof-to-wall intersection. Its job is to “kick” water away from the wall and direct it into the gutter.
Think of it as a tiny traffic director for rainwater. Step flashing handles the water along the wall as shingles climb the roof slope. The kickout flashing handles the critical endpoint, where that water needs to leave the wall and enter the gutter instead of sliding behind the siding.
According to InterNACHI’s explanation of kickout flashing, missing or poorly installed kickout flashing can allow water to enter behind exterior wall coverings. That can lead to rot, mold, damaged sheathing, stained interior walls, and structural repairs.
The part is small, but the consequences of leaving it out can be large.
Why roof-to-wall intersections are so vulnerable
Roof systems are designed to move water down and away. Walls are designed to shed water vertically. Where those two planes meet, the details matter.
At a sidewall, rainwater can collect and travel along the step flashing. If there is no kickout at the bottom, water may:
Run past the gutter instead of into it
Flow behind brick veneer, stucco, vinyl siding, or fiber cement siding
Wet the wall sheathing
Soak insulation
Damage trim and framing
Create conditions for mold growth
This kind of leak often stays hidden. The siding may look fine from the outside while the sheathing behind it slowly deteriorates. In many cases, the first clue is peeling paint, a soft wall, a musty smell, or an interior stain near a ceiling line.
Good flashing is not just about stopping visible leaks. It is about controlling water before it reaches places that cannot dry easily.
How kickout flashing works with step flashing
Kickout flashing does not work alone. It is part of a larger flashing system.
Along a roof-to-wall intersection, individual pieces of step flashing are installed with each course of shingles. Each piece overlaps the one below it, similar to shingles, so water drains down the roof without reaching the wall assembly.
At the bottom of that run, the kickout flashing creates a diverter. Its vertical leg sits against the wall. Its base lies under the shingles. Its angled lower portion projects outward to guide water into the gutter.
When installed correctly, water follows this path:
Rain lands on the roof.
Shingles shed water downward.
Step flashing protects the sidewall.
Kickout flashing redirects the water outward.
The gutter collects and carries the water away.
When the kickout is missing, that last step fails. Water can slip behind the wall covering right where runoff is most concentrated.
Common materials used for kickout flashing
Kickout flashing must resist corrosion, hold its shape, and work with the rest of the roof system. Common materials include:
Material | Why it is used | What to watch for |
Galvanized steel | Strong, common, and cost-effective | Cut edges can rust if not protected |
Aluminum | Lightweight and easy to form | Can react with some treated lumber or metals |
Copper | Long-lasting and corrosion-resistant | Higher material cost |
Stainless steel | Very durable in harsh conditions | More expensive and harder to form |
PVC or other approved plastics | Often used with some modern siding systems | Must be compatible with roof materials and climate exposure |
The best choice depends on the roofing material, siding type, climate, and local code requirements. Metal is common because it is rigid and durable, but compatibility matters. Mixing certain metals can cause corrosion when moisture is present.
For example, copper and aluminum should not be placed together in a way that allows ongoing contact with water. A roofing professional should choose materials that work as a system.
Installation tips that make the difference
Kickout flashing has to be installed in the right order. Caulk alone is not a substitute. Sealant can crack, shrink, or separate over time, especially on a roof exposed to sun, rain, snow, and movement.
A proper installation usually includes these key practices.
Place it at the bottom of the roof-to-wall intersection
The kickout belongs where the sidewall meets the roof edge near the eave or gutter. It should catch water coming off the step flashing and direct that water into the gutter.
If it stops short, sits behind the gutter incorrectly, or points the wrong way, it cannot do its job.
Integrate it with housewrap and wall flashing
The vertical leg should work with the wall’s water-resistive barrier. Water that gets behind siding needs a path back out, not a path into the wall.
Good installation often requires careful layering: wall underlayment, step flashing, shingles, siding clearance, and trim all need to overlap in a way that drains outward.
Use proper overlap with shingles and step flashing
The kickout should tuck under the first course of shingles and tie into the step flashing. Water should always lap over the next lower material, never behind it.
A simple rule helps: every upper layer should shed onto the layer below.
Keep siding raised above the roof surface
Siding should not sit tight against shingles. A small clearance helps reduce moisture wicking and makes it easier to see the flashing. This is especially important with wood and fiber cement siding.
Avoid relying on caulk as the main defense
Sealant can help in specific joints, but it should never be the main water-control strategy. Mechanical flashing and proper overlap do the real work.
InterNACHI’s roofing inspection resources, including its flashing inspection guidance, stress the role of correct flashing details in preventing water intrusion. The lesson is simple: placement and layering matter more than appearance alone.
Signs kickout flashing may be missing or failing
A kickout flashing problem is often easiest to spot from the exterior. Look near the lower end of a roof section that meets a wall.
Common warning signs include:
Stains on siding below a roof edge
Rotting trim near the gutter
Peeling paint in one concentrated area
Soft or swollen wall materials
Water stains inside near the ceiling
Mold or musty odors near the affected wall
Gutters that are present, but water still runs behind them
A home inspector or roofing contractor can often identify missing kickout flashing during a roof inspection. In some cases, correction may be simple. In others, siding, roofing, or damaged sheathing may need repair.
Why proper installation supports long-term roof performance
A roof is only as reliable as its weakest water-control detail. Shingles may be in good condition, gutters may be clean, and the attic may look dry, but one missing kickout flashing can still send water where it does not belong.
Proper kickout flashing helps:
Protect wall sheathing and framing
Extend the life of siding and trim
Reduce the chance of hidden leaks
Support gutter performance
Preserve the roof’s drainage design
Lower the risk of expensive moisture repairs
For new roofs, kickout flashing should be part of the original installation. For existing homes, it is worth checking during roof repairs, siding replacement, gutter work, or a home inspection.
The takeaway is straightforward: kickout flashing is a small part with a big job. When it is properly selected, layered, and installed, it keeps water moving in the right direction. That protects the roof, the walls, and the home behind them.
Comments