Architectural Flashing Supply
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Failure analysis and forensic diagnosis · Lesson 2 of 4

Failure analysis and forensic diagnosis: materials, standards and design constraints

Oil canning and thin flat faces; restrained thermal movement and cleat practice; expansion by material; wind zones on the roof edge; the ES-1 tests; why a tested capacity belongs to one assembly; and corrosion rates as first-year ranges.

You will be able to: Connect each failure mode the published record supports to its mechanism and the evidence to expect, use the AFS register values for movement, read an edge-wind demand and a tested capacity correctly, and read a corrosion rate as a first-year range.

12 min · 12 slides · 9 questions

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Slide 1 of 12

Oil canning: width and thickness

MCA attributes oil canning to differential stresses within the metal: panels with a high width to thickness ratio buckle out of plane.

The waves grow as the flat width increases or the thickness decreases.

In general, MCA says, the thicker the metal, the less likely a panel is to oil can.

MCA gives no width-to-thickness threshold, so this course states none.

Flat width over thickness by gauge, 12 in faceBar chart of a hypothetical 12 in flat face divided by galvanized sheet thickness from the AFS gauge register: 16 gauge 189, 18 gauge 233, 20 gauge 303, 22 gauge 357, 24 gauge 435, 26 gauge 553. Thinner metal has a higher ratio. MCA gives no threshold.Thin metal, wide flat faceHypothetical 12 in flat face020040060018916 ga23318 ga30320 ga35722 ga43524 ga55326 gaFlat width divided by thickness (no units)Thinner metal gives a higher ratio, andMCA says higher ratios buckle more. MCAgives no threshold, so none is drawn.Thickness is one of several causes.Thickness: AFS galvanized gauge register

Bar chart of a hypothetical 12 in flat face divided by galvanized sheet thickness from the AFS gauge register: 16 gauge 189, 18 gauge 233, 20 gauge 303, 22 gauge 357, 24 gauge 435, 26 gauge 553. Thinner metal has a higher ratio.

Hypothetical 12 in face over the AFS galvanized gauge thicknesses. MCA says higher width-to-thickness ratios buckle more but gives no threshold, so none is drawn; thickness is one of several causes.

Sources

Videos for this lesson

What this video shows: A testing laboratory's short clip of a coping pull-off under the ANSI/SPRI/FM 4435 ES-1 RE-3 method. Checked against the video's description; no values are taken from it.

Video: ANSI/SPRI ES-1 Coping Pull Off - RE-3 Test by National ES Testing Service Tunney, on YouTube. Chosen from the video's published description.

Glossary

Oil canning
Visible waviness in the flat areas of metal panels, technically elastic buckling or stress wrinkling. MCA calls it generally an aesthetic issue.
Dual pinning
A detail where a panel or flashing is held at two points that should let it move, so expansion is restrained and can show as waves or damage fasteners.
Cleat
A strip that holds the edge or hem of a flashing; IBHS advises slotted or oversized fastener holes so the metal can move.
ES-1
The ANSI/SPRI/FM 4435/ES-1 test standard for roof edge metal. Its RE-1 tests membrane restraint (required only for some membranes), RE-2 the outward pull on a vertical face, and RE-3 a coping top and face together.
Suction coefficient (GCp)
A dimensionless number from ASCE 7 that, with wind speed and height, sets the suction on a part of the building; a roof corner has a larger one than the perimeter.
Tested capacity
The load an exact assembly resisted in a lab test. It applies only to that product, metal, gauge, cleat, splice and spacing.