Kickout Flashing: Install It Before Walls Rot

One small bent piece of metal prevents more hidden wall rot than almost anything else on a house. Kickout flashing sits at the bottom of a roof-to-wall intersection, right where the roof edge dies into a sidewall, and kicks the water running down the step flashing out into the gutter. Without it, that water dumps behind the siding and soaks the sheathing, framing and sometimes the window below for years before anyone notices.

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The short answer: if your roof edge stops against a wall that keeps going down past the eave, you need a kickout (also called a diverter flashing). It costs very little and is required by most current residential codes. Retrofitting one is usually a matter of removing a few courses of siding, installing a preformed diverter under the housewrap and lapping everything back in the right order.

Inspectors call missing kickouts one of the most common sources of concealed water damage they find, especially on houses with stucco, stone veneer and fiber cement siding.

Why Kickout Flashing Matters

Step flashing carries water down the length of a roof-to-wall joint. At the bottom of that run, all the collected water needs somewhere to go. If the gutter ends short of the wall, or there is no diverter, the water flows off the last step and directly onto the wall surface or behind it. A single rainstorm can send gallons into that one corner.

The damage is slow and quiet. Water soaks the sheathing behind the siding, rots the bottom plate and studs and often runs down into the window header or door frame beneath the intersection. By the time you see stains, bubbling paint or soft trim, the framing can be badly decayed. Mold usually follows, because the wall cavity stays damp and dark.

A kickout flashing roof detail fixes this with a simple diverter: a closed, angled piece that sits beneath the bottom step and throws water outward past the face of the siding into the gutter.

Where You Need One

• Any place a lower roof eave meets a taller sidewall: garage roofs against a two-story wall, porch roofs, dormers and additions.
• Roof-to-wall intersections above windows, doors or decks, which are especially vulnerable.
• Walls clad with stucco, adhered stone or brick veneer, which hide damage longer than lap siding.
• Any intersection where the gutter ends against the wall rather than extending past it.

Walk the house in a heavy rain if you can. Look for water sheeting down the wall below a roof edge, streaking on siding, or splash marks on the ground in that corner.

Signs of a Missing or Failed Kickout

• Vertical stains or peeling paint on the wall beneath where a roof edge meets it
• Soft or swollen trim around a window or door below the intersection
• Cracked or bulging stucco or stone veneer in a triangle shape below the roof edge
• Interior drywall stains or musty smells on the room side of that wall
• A homemade kickout made from a bent step flashing that is open at the bottom or tipped toward the wall

Tools and Materials

• Preformed kickout flashing (one-piece molded plastic or soldered metal; avoid open-ended bent pieces)
• Siding removal tools (flat bar, siding zip tool for vinyl, oscillating tool)
• Self-adhered flashing tape and housewrap patches
• Roofing nails, siding nails and exterior sealant
• Moisture meter, awl or screwdriver for probing sheathing
• Replacement sheathing or framing lumber if rot is present
• Gloves, eye protection and an N95 respirator if you find mold

How to Retrofit Kickout Flashing Under Siding

1. Remove the siding. Take off enough siding at the bottom of the roof-to-wall joint to expose the lowest step flashing and a foot or two of wall beneath it. On vinyl, unlock courses with a zip tool; on fiber cement or wood, pull nails carefully to reuse boards.
2. Inspect the wall. Probe the sheathing and bottom plate with an awl. Read the moisture meter. Anything soft, black or reading well above surrounding wood needs repair before new flashing goes on.
3. Repair and dry. Cut out rotted sheathing back to sound wood, replace damaged framing and let everything dry. Fix the moisture source first; flashing over wet wood traps the problem.
4. Lift the shingles and lowest step. Gently break the seal on the bottom shingles at the wall and slide out the last step flashing if needed.
5. Position the kickout. Set it as the first piece at the bottom of the step run, with its diverter extending past the roof edge and over the gutter. The angled end should point out and slightly down so water cannot run back toward the wall.
6. Fasten and lap. Nail it to the roof deck only, high on the flange. Lap the next step flashing over it by at least 2 inches. Shingles lap over the roof leg as normal.
7. Integrate the housewrap. The wall leg of the kickout goes behind the housewrap. Slit the wrap above, slip it over the kickout’s vertical leg and seal the slit with flashing tape, shingle style, so water on the wrap drains onto the flashing.
8. Reinstall the siding. Leave a 1 to 2 inch clearance between siding and the roof surface along the joint, and cut the siding around the kickout without blocking its outlet.
9. Check the gutter. Extend the gutter end cap so the kickout empties directly into it. A gutter that stops short defeats the whole detail.

Common Installation Mistakes

• Reverse lap at the housewrap. Tucking the kickout over the wrap instead of behind it sends water straight into the wall.
• Caulk instead of flashing. A bead of sealant at the corner fails within a few seasons and is not a substitute.
• Open-ended homemade diverters. A step flashing bent outward leaks at the open corner. Use a closed, one-piece product.
• Siding tight to the roof. Siding that touches shingles wicks water and rots. Keep the clearance gap.
• No room for the gutter. The diverter must clear the fascia and land over the gutter trough.

Mold and Moisture: Fix the Source First

When you open a wall that has been wet for years, expect mold on the sheathing and framing. Stop the water first, which is exactly what the new flashing does, then dry the cavity fully before closing it up. Small areas of surface mold on wood can be cleaned with detergent and water while wearing gloves, eye protection and an N95 respirator, then dried thoroughly. If the moldy area is larger than about 10 square feet, has spread into insulation or drywall, or anyone in the home has respiratory sensitivity, hire a mold remediation professional who can contain the work area and use HEPA filtration.

Replace wet insulation rather than drying it in place, and confirm the framing is dry with a moisture meter before adding new sheathing, a water-resistive barrier and siding.

Cost Ranges

The diverter itself is inexpensive, usually a small purchase per piece. A straightforward retrofit by a roofer or siding contractor, with no rot, often runs a few hundred dollars per intersection. Once rot repair, sheathing replacement and mold remediation enter the picture, costs climb quickly into the thousands, which is why installing kickout flashing early is so much cheaper than fixing what happens without it.

Ladder Safety and When to Call a Pro

Many kickouts sit where a one-story roof meets a two-story wall, so you are often working on a roof surface beside a tall wall. Set extension ladders on firm, level ground at a 4-to-1 angle, extend them 3 feet past the roof edge and secure the top. Wear soft-soled shoes, stay off wet or frosty roofs and use a harness anchored to the framing on steeper pitches. For any work two stories up or on a steep roof, hire a pro.

Call a roofing or siding contractor when the intersection involves stucco or adhered stone, which requires careful cutting and patching, or when probing reveals soft framing. A carpenter or general contractor should handle structural repairs, and a mold professional should handle contamination larger than about 10 square feet.