Looking at a job a sub did last week: shingle roof runs into a stucco sidewall.

It will leak—guaranteed. You have three code violations creating a funnel into the wall.

1. Missing Kickout Flashing (IRC R903.2.1 / IBC 1503.2): Where a roof terminates at a sidewall, a kickout diverter is mandatory to direct water into the gutter. Without it, high-volume runoff tracks down the vertical flashing leg, overwhelms the caulk bead, and penetrates the stucco/WRB interface.
2. Improper Flashing Method (IRC R905.2.8.3 / ARMA/NRCA): Continuous "L-flashing" (headwall flashing) is prohibited for shingle sidewalls. You must use step flashing (individual pieces interwoven with each shingle course). Continuous flashing relies solely on that polyurethane bead—a maintenance item, not a roofing system. Thermal movement will fracture the bond within 2–3 years.
3. Gutter Termination (IRC R903.4.1): The gutter must extend past the sidewall intersection to catch the kickout discharge. Stopping 4" short dumps water directly onto the wall cladding.

The Fix (requires tear-off):

1. Remove shingles & flashing back 2–3 courses from wall.
2. Install step flashing (min. 4"x4", corrosion-resistant) woven into each course.
3. Install kickout flashing at bottom course, sealed to step flashing & WRB.
4. Counter-flash vertical leg into stucco reglet (cut 1" deep) or behind WRB—do not surface-mount with screws/caulk.
5. Extend gutter to capture kickout flow.

Bottom line: The sub installed a "caulk job," not a roof. Tell the GC it fails IRC R903.2.1 and manufacturer specs. It’s a re-do.

This detail is fundamentally flawed and will likely lead to water intrusion and damage over time. Here’s why:

1. No Kickout Flashing: The absence of a kickout (diverter) flashing at the roof-to-wall intersection is a critical defect. Per IRC R903.2.1 and IBC 1503.2, kickout flashing is required where a roof edge terminates at a vertical wall to divert water away from the wall and into the gutter. Without it, water running down the roof will hit the wall directly, wicking behind the stucco or entering at the L-flashing termination.

1. Improper L-Flashing Installation: While L-flashing (continuous under shingles, vertical leg screwed to stucco) is acceptable if properly integrated, screwing the vertical leg directly into stucco without a water-resistive barrier (WRB) behind it creates a penetration path. Stucco is not a WRB; moisture can track behind it via capillary action or at fastener holes. The polyurethane bead on top is insufficient—it will degrade, crack, and fail, especially with UV exposure and thermal cycling.

1. Gutter Setback: Stopping the gutter 4 inches short of the wall defeats its purpose. Water will overflow or run back toward the wall, especially during heavy rain or ice buildup, exacerbating the lack of kickout protection.

What Will Happen:

• Water will penetrate behind the stucco at the roof-wall junction, leading to staining, efflorescence, mold, and eventual rot of sheathing or framing.
• Stucco may crack or spall due to freeze-thaw cycles behind it.
• Interior leaks may appear at ceilings or walls near the intersection, often misdiagnosed as roof or plumbing issues.
• The "clean" look is temporary—cosmetic, not functional.

Correct Fix: Remove the existing flashing. Install proper kickout flashing (prefabricated or site-formed) that extends over the roofing and behind the WRB (housewrap or felt) on the wall, with the vertical leg lapped over the WRB and sealed with compatible sealant or backer rod. Gutter must run tight to the wall or include a diverter to direct flow into it. This is a roofing/waterproofing detail—licensed roofer or contractor should repair.

Note: If stucco is EIFS or barrier system, risk of hidden damage is higher. Recommend moisture probe inspection.