Architectural Flashing Supply
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Forensic water intrusion diagnosis · Lesson 4 of 4

Forensic water intrusion diagnosis: defects, verification and case study

Six sheet-metal entry mechanisms from the Failure Atlas and the cited guides; a constructed case walked through the method; retesting; corrections with the warranty first; the leak that was not a leak; and a conclusion that can be defended.

You will be able to: Diagnose a plausible sheet-metal-related entry mechanism from its evidence, explain correction options with the warranty first, verify by retesting the same way, and write a conclusion that states its evidence and its limits.

10 min · 12 slides · 6 questions

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Slide 1 of 12

Joints and sealant

Unsealed or unspliced joint: BSC says leaks often occur at lapped joints between lengths of rigid flashing; Drexel's guides call for a splice plate at every joint.

The AFS Failure Atlas lists poor joint design, such as no backer rod, the wrong width-to-depth ratio or three-sided adhesion, among the causes of sealant failure.

Sources

Videos for this lesson

What this video shows: Forensic case studies where unaccounted movement led to enclosure failures, including an under-sloped roof with ponding. A case-study talk, not a leak-diagnosis method.

Video: Buildings Move, Buildings Leak: Engineering-Enclosure Link (Jon Porter, 2026 Westford Symposium) by BuildingScience-com Corporation, on YouTube. Chosen from the video's published description.

Glossary

Fatigue cracking
In the AFS Failure Atlas, cracking from daily and seasonal thermal cycling concentrated at one seam, fastener or bend where the detail gave no expansion relief.
Ponding
In the AFS Failure Atlas, standing water from too little slope, blocked or undersized drains, scuppers or gutters, or failed expansion joints and seams that form a dam.
Crevice corrosion
Corrosion in tight, poorly drained gaps under washers, in unsealed laps or behind debris that hold water. The AFS Failure Atlas says to re-detail the crevice so it drains and dries, or seal it fully, never half-seal it.
Defensible conclusion
This course's term for a conclusion that names the most probable entry, the evidence for it, the alternatives ruled out, what was not tested and the limits, without claiming more than the evidence shows.