Stucco Around Roof-to-Wall Kickout Flashing: Fixing the Most Common Leak Detail

Kickout flashing directs roof runoff away from the wall cladding where the roof meets a vertical surface. When stucco is the cladding, its rigid finish and lath attachment can hide water entry and trap moisture behind the plaster.

These transitions concentrate water flow at a small junction and any gap, misalignment, or missing flashing becomes a high-risk leak point. Check product labels or manufacturer instructions for compatibility with stucco assemblies and confirm local practice if you are unsure.

Function of kickout flashing

Kickout flashing plays a crucial role at roof-to-wall transitions. Its primary function is to divert water runoff from the roof, preventing it from cascading down the wall.

Properly installed, it changes the direction of water flow, guiding it safely away from the wall and into gutters or downspouts.

Without kickout flashing, water can pool at the roof-to-wall junction, leading to leaks and potential damage to both the roof and wall systems.

Why stucco interfaces are vulnerable

Stucco, while durable, has specific properties that make it susceptible to leaks at roof-to-wall junctions. Understanding these can help you address potential issues.

The lath and wire mesh used in stucco construction can trap water if not properly protected by a weather-resistant barrier (WRB). This trapped water can lead to leaks over time.

Additionally, the rigid nature of stucco finishes means that any movement or settling of the building can crack the stucco, creating pathways for water intrusion at these critical junctions.

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The flashing must be layered so that it slips under the roofing underlayment above the roofline and over the water-resistive barrier (WRB) against the wall, with stucco lath and plaster terminating correctly. Proper sequencing forces any water that gets behind the roofing to follow the plane of the flashing out and away from the wall.

Match details to the specific WRB and lath system you have and consult product data sheets for overlap and attachment instructions. If a component’s installation isn’t clear, verify with the manufacturer or local code guidance before cutting or fastening.

Proper sequencing and overlap

The order of installation is crucial to ensure a watertight system. Here’s how it goes:

1. Roof underlayment: Start with your roofing felt or synthetic underlayment. It should extend at least 6 inches past the wall line.

2. Kickout flashing: Next, install the kickout flashing. It should overlap the roof underlayment by a few inches and extend down the wall at least 4 inches.

3. Water-resistive barrier (WRB): Now, apply your WRB. It should overlap the kickout flashing by a few inches and extend up the wall to meet the stucco lath. Use tape or liquid flashing to seal any seams.

4. Stucco lath: Finally, attach your stucco lath over the WRB. Make sure it’s secured tightly and extends at least 6 inches above the kickout flashing.

Water-resistive barrier and stucco lath relationship

The WRB and stucco lath work together to keep water out while allowing any moisture that gets in to drain. Here’s how:

WRB termination: The WRB should be terminated at the top of the wall, just below where the stucco will start. It should be secured tightly and any seams should be sealed with tape or liquid flashing.

Lath/mesh attachment: The stucco lath should be attached to the wall in a way that allows for drainage. This usually means using screws or nails that are long enough to penetrate the sheathing but not so long that they go through it. The lath should also be spaced appropriately (usually 6 inches on center) to allow for good drainage.

Remember, the goal is to create a system where water can drain out of the wall while preventing it from wicking back up. So, keep everything tight and well-sealed at the top, but allow for drainage at the bottom.

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Leaks usually stem from improper flashing termination, gaps at the WRB transition, poorly lapped roofing underlayment, or mechanically damaged or corroded flashing. Stucco-specific issues include lath cut too short, plaster terminating over flashing instead of above it, and failure to maintain a through-wall drainage plane.

Material incompatibilities or improper fastener placement also open leak paths; check manufacturer instructions for permitted fasteners and sealants. When in doubt about a product pairing or expected lifespan, look it up on the product data sheet or ask the maker.

Improper flashing termination and gaps

The most common leak cause is improperly terminated kickout flashing. Water flows down the roof, hits the wall, and needs a path out. If the flashing doesn’t extend far enough or laps incorrectly, water gets trapped and pushed into the wall.

Check for these issues:

Insufficient extension: Flashing should stick out at least 4 inches beyond the stucco edge. Less than that lets water sneak behind it.

Incorrect laps: Flashing pieces should overlap, with the upper piece lapping over the lower one. Reverse laps force water into the wall.

Stucco cracking and separation at the junction

Cracks or separations at the stucco-flashing junction let water in. This happens due to settlement, poor bonding, or inadequate expansion joints.

Inspect for:

Cracking: Hairline cracks can grow and allow water entry. Fill with a flexible sealant designed for masonry.

Separation: If stucco pulls away from the flashing, water will get in. Ensure proper bonding at installation and address any separations with an appropriate sealant.

Expansion joints: Stucco moves with temperature changes. Without expansion joints, this movement can cause cracking. Include expansion joints every 10-15 feet.

Material incompatibility and corrosion

Using incompatible materials speeds up degradation of the flashing-stucco interface, leading to leaks. Choose compatible metals, sealants, and backer materials.

• Galvanized vs. stainless steel: Galvanized steel can corrode where it contacts stucco. Stainless steel is more durable but costs more.
• Sealant type: Use a flexible, masonry-grade sealant. Silicone or acrylic caulks aren’t suitable for this application.
• Backer material: Use a water-resistive barrier rated for exterior use. Some barriers degrade over time and let water in.
• Paint/stain: Avoid applying paint or stain to the stucco-flashing junction. This traps moisture and can cause peeling, cracking, or corrosion.
• Fasteners: Use fasteners designed for exterior use with proper spacing. Incompatible fasteners can corrode or pull out, allowing water entry.

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Start with a visual sweep from the roof above the junction, then inspect the wall face and soffit below for staining, blistering, or efflorescence that indicate moisture tracking. Look for gaps, torn WRB, improperly lapped underlayment, and where the lath and stucco terminate relative to the flashing.

Perform simple noninvasive checks like water testing small sections and probing visible joints with a thin tool to find soft spots. If you find ambiguous damage, consult the product installation instructions or a professional for intrusive inspection options before major demolition.