Base counterflashing and reglet fabrication · Lesson 2 of 4

Base counterflashing and reglet fabrication: materials, standards and design constraints

The 0.019 in code minimum and the gauge trap, minimum metals by document, copper tempers, lead and mixed metals, manufacturer reglet systems, and laps and lengths that change with the governing document.

You will be able to: State the code minimum thickness and why gauge alone does not prove it, compare the metal minimums and laps different documents set, and choose metals that will not corrode each other.

13 min · 12 slides · 11 questions

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Slide 1 of 12

The code minimum

The IRC text as adopted in Minnesota requires metal flashing to be corrosion resistant and at least 0.019 in thick (No. 26 galvanized sheet).

IBC 2015 section 1503.2, as Graham quotes it, sets the same 0.019 in; adopting texts such as the 2021 Seattle code put that sentence in subsection 1503.2.1.

These are model and other jurisdictions' texts: the edition your local authority has adopted governs.

Sources

Minnesota Rules 1309.0903 - International Residential Code section R903.2.1 Flashing, as adopted and amended (version 2020-03-31) - State of Minnesota, Office of the Revisor of Statutes
Metal flashing thicknesses (Mark S. Graham), Professional Roofing, November 2017 - National Roofing Contractors Association (Professional Roofing)
2021 Seattle Building Code, Chapter 15 Roof Assemblies and Rooftop Structures (IBC-based) - City of Seattle, Department of Construction and Inspections

Glossary

Nominal thickness: The named thickness of a gauge; the ASTM tolerance lets a sheet run thinner or thicker than it.
Temper (H00, O60): How hard the copper is: H00 cold-rolled, O60 soft, used where forming needs it.
Dissimilar metal corrosion: Corrosion of the less noble of two metals in contact or wetted by runoff from the more noble one, as copper attacks steel, aluminum and zinc.
Guide specification: A model specification a designer edits for a project, such as the CDA 14.5 or UFGS 07 60 00; binding only when the project uses it.