Architectural Flashing Supply
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Flashing geometry and movement accommodation · Lesson 4 of 4

Flashing geometry and movement accommodation: defects, verification and case study

Defects that come from the drawings rather than the field, what the sources say about oil canning, a drawing review checklist, and a fictional case study rewritten from range to fabrication check.

You will be able to: Diagnose movement defects that start in the drawings, explain the corrective options, and record the calculation, the marked-up detail and the review for a run of flashing.

11 min · 12 slides · 8 questions

All lessons in this module
Slide 1 of 12

Defect: both ends held

PAC-CLAD advises against rigidly fixing both ends of a long panel, and says most panels are attached at the ridge, so expansion runs down the panel.

AFS's Failure Atlas lists too little allowance for thermal expansion as a cause of oil canning, because a panel restrained against movement bows.

A panel held at both ends compared with one fixed pointTwo roof sections. In the wrong one a panel is fixed at the eave and at the ridge and buckles in the middle. In the right one a single fixed point holds the panel and sliding clips let the rest move.Wrong: both ends heldFFbucklesNowhere for the movement to goRight: one fixed pointFSfree end movesPanel maker sets where it is heldSchematic roof section, not to scale

Two roof sections. In the wrong one a panel is fixed at the eave and at the ridge and buckles in the middle. In the right one a single fixed point holds the panel and sliding clips let the rest move.

F
Fixed point
S
Sliding clip
PAC-CLAD advises against rigidly fixing both ends of a long panel. Where the single fixed point goes is set with the panel maker. Schematic, not a maker's detail.

Sources

Videos for this lesson

What this video shows: The channel's description says it defines oil canning, explains its causes, covers prevention before and during installation and asks whether any fixes exist afterwards.

Video: Interested in Metal Roofing? You Need to Know This About Oil Canning! by The Metal Roofing Channel, on YouTube. Chosen from the video's published description.

Glossary

Oil canning
Visible waviness of a flat metal face; PAC-CLAD says it does not affect finish or structural integrity, and ED-1 says thicker metal reduces the oil-can effect.
Face bowing
Bowing of the exposed face of a roof edge component that ED-1 says can follow from elements that cannot expand and contract freely.
Fatigue cracking
Cracking where daily and seasonal thermal cycling concentrates at one seam, fastener or bend; AFS's Failure Atlas links it to a detail with no expansion relief.
Appliance
Equipment such as an air terminal, sign or antenna attached to a roof edge system; ED-1 says it can restrain movement.
RFI
A request for information: a written question to the designer, kept in a log with its answer, used when documents disagree.