Architectural Flashing Supply
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Failure analysis and forensic diagnosis · Lesson 4 of 4

Failure analysis and forensic diagnosis: defects, verification and case study

Three FEMA 488 school cases and an IIBEC leak case; where to look on a coping; corrective options and what each addresses; causes outside the metal; verifying a repair; and writing a finding.

You will be able to: Read a published case and separate fact from inference, say when a cause cannot be determined, choose a corrective option by the condition it addresses, and verify a repair.

10 min · 10 slides · 7 questions

All lessons in this module
Slide 1 of 10

Case 1: Cape Coral middle school

FEMA 488 reports that at a Cape Coral middle school, first occupied in 1998, the metal edge flashing had been installed underneath the membrane.

It should have been over the modified bitumen cap sheet and stripped in to clamp the edge.

Wind lifted the gutter and edge flashing and peeled the membrane.

The 2 in vertical flange extended into the gutter and was not cleated.

Edge flashing over or under the membraneTwo roof edge sections. Left, intended per FEMA 488: edge flashing laid over the membrane and stripped in, with a cleat and a slotted hole, marked correct. Right, as observed at two schools: flashing under the membrane, which stops short of the edge, with a vertical flange running into a gutter and no cleat, marked incorrect. Labels A over or under the membrane, B cleat, C flange into the gutter, D slotted hole. Not to scale.Edge flashing: over or under?IntendedObservedABDCALeft: FEMA 488 says the flashing should goover the cap sheet and be stripped in so itclamps the membrane edge.Right: FEMA 488 reports flashing under themembrane at two schools; at one the membranepeeled, at the other nothing lifted.Not to scale; metal in charcoal outline

Two roof edge sections. Left, as FEMA 488 says it should be: flashing over the membrane and stripped in, with a cleat and a slotted hole, marked correct. Right, as observed at two schools: flashing under the membrane, with a flange running into a gutter and no cleat, marked incorrect.

A
Membrane edge and strip-in line: whether the flashing sits over or under the membrane
B
Cleat
C
Flange running into the gutter
D
Slotted fastener hole
FEMA 488 describes the right-hand detail at two schools; at one the membrane peeled, at the other nothing lifted. Schematic, not to scale; the slotted hole is an IBHS practice.

Sources

Glossary

Progressive failure
A failure in which one released part exposes the next, such as a lifted gutter lifting the edge flashing and then peeling the membrane.
Strip in
To cover the edge of a metal flashing flange with membrane plies so the flashing clamps the membrane edge, as FEMA 488 says the Cape Coral flashing should have been.
Peel-stop bar
A bar anchored over the membrane near the roof edge as secondary protection against membrane lifting and peeling if the edge metal fails.
Verification
Showing a repair worked: the test that reproduced the problem before the repair no longer does.
Finding
A written conclusion that states what was observed, what it is consistent with, a confidence word, and what would change it.