Metal roofs, walls and rainscreens · Lesson 4 of 4

Metal roofs, walls and rainscreens: defects, verification and case study

A rating misapplied, seams that let go, slope and water mismatches, oil canning from restraint, blocked rainscreen cavities, MCM above 40 feet, thin metal, the evidence packet and a constructed clinic roof case.

You will be able to: Diagnose eight common defects in metal roofs and walls, name the evidence that verifies an installed system, and work a constructed case study from symptoms to documented corrective options.

12 min · 11 slides · 11 questions

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Slide 1 of 11

Eight defects to look for

Eight common defects: a rating misapplied; a seam that lets go; a panel below its slope floor; the wrong water strategy; oil canning from restraint; a blocked or broken rainscreen; MCM above 40 feet with no NFPA 285 record; and metal below the table minimum.

Sources

2021 Seattle Building Code, Chapter 15 Roof Assemblies and Rooftop Structures (the 2021 International Building Code as adopted by Seattle): 1504.4, 1507.4 - City of Seattle, Seattle Department of Construction and Inspections
2021 Seattle Building Code, Chapter 14 Exterior Walls (the 2021 International Building Code as adopted by Seattle): 1404.11, 1406 - City of Seattle, Seattle Department of Construction and Inspections
Metal Roof Installation Manual, Chapter 4 Panel Types - Metal Construction Association

Glossary

Sidejoint disengagement: The failure recorded in a 2005 UL 1897 report for a 16 in Snap-Clad aluminum panel at 107.7 psf: the seam between neighbouring panels came apart.
Dual pinning: MCA's term, among the installation causes of oil canning, for restrained movement where a panel is pinned at both ends.
Bridged cavity: A rainscreen cavity crossed by insulation or debris so it can no longer drain and dry water, as MCA describes the cavity's job.
Re-evaluation date: The date a TDI product evaluation is due for review; the RC-320 draft revision shows November 2024, which has passed, so check TDI's current list before citing it.