Why is reverse-lapped louver flashing a serious water problem?

Field answer

Exterior flashing works like shingles: upper layers must drain onto lower layers. If the head flashing is placed on the wrong side of the weather barrier, water can run behind the flashing into the wall cavity.

Stop covering work, expose the head condition, and coordinate the correct lapping detail with the GC/envelope trade. Usually the top leg must be integrated behind the weather barrier or approved flashing tape system, with side/end detailing per the project envelope detail.

What to check first

• Check whether the weather barrier laps over the head flashing correctly.
• Look for a reverse-lap path into the wall cavity.
• Verify the exterior wall/envelope detail, not just the mechanical drawing.
• Do not cover the condition with siding or trim.
• Photograph the lap sequence before correction.

Why it matters

Wrong flashing sequence can cause hidden wall rot and major water intrusion.

Ask foreman

Text this wording

Related Field Rescue route

Open routeBack to Q&A

Final direction belongs to the foreman, approved drawings/specs, manufacturer instructions, pressure/material schedule, employer policy, and AHJ/code requirements.