Product selection and substitutions · Lesson 2 of 4

Product selection and substitutions: materials, standards and design constraints

What equality has to cover on a flashing assembly: how gauge, weight and decimal-inch thickness differ by metal, how much each metal moves, which metals should not share runoff, and why a wind rating belongs to a whole tested assembly.

You will be able to: Compare two candidate products on thickness, thermal movement, galvanic behavior, finish evidence and tested-assembly status, and state which constraints a substitution can break.

13 min · 12 slides · 10 questions

All lessons in this module

Slide 1 of 12

Equality is a list

Significant qualities may include performance, weight, size, durability, visual effect, warranties and specific features.

For an edge assembly this module's checklist adds thickness, thermal movement, contact with other metals, finish and color, cleat and fasteners as tested, the wind-tested assembly and the warranty.

Each of the lettered items A to G is a line to compare.

A: Metal and thickness
B: Thermal movement
C: Contact with other metals (galvanic)
D: Finish and color match
E: Cleat and fasteners as tested
F: The wind-tested assembly as a whole
G: Warranty

This module’s checklist for an edge assembly, built from the University of Houston list of significant qualities, IIBEC, SPRI and NRCA. Exploded and not to scale.

Sources

Section 01 25 00 Substitution Procedures, master specification (revision 01/29/2018) - University of Houston Master Construction Specifications (AIA-copyrighted master text)
Section 01 60 00 Product Requirements, master specification (revision 01/29/2018) - University of Houston Master Construction Specifications (AIA-copyrighted master text)

Glossary

Gauge: A number that names a sheet thickness, which differs from one metal to the next: 24 gauge is 0.0276 in in galvanized steel and 0.0201 in in aluminum, in one distributor table.
Thermal movement: The change in length of a piece when its temperature changes, found as the coefficient times the length times the temperature change.
Galvanic corrosion: Corrosion that can occur when two dissimilar metals touch in the presence of moisture, usually worse the farther apart they sit in a galvanic series.
Tested assembly: The exact set of parts a wind test was run on: cover, cleat, fasteners and size. A changed part is a different assembly.
Sustained pressure: The outward pressure, in psf, that a manufacturer publishes for a tested edge system; the design engineer applies the factor of safety.