Compound transitions and complex forms · Lesson 1 of 4

Compound transitions and complex forms: principles and terminology

What makes a flashing piece complex: cones, transitions, unequal and peak miters, crickets and radius coping; the words of radial line and triangulation; and the hazards of cut edges, lead solder and flame.

You will be able to: Tell a straight prism from a complex form, name the three pattern development methods and their terms, and state the safety boundaries for cut edges, solder and hot work.

10 min · 12 slides · 6 questions

All lessons in this module

Slide 1 of 12

What this module covers

Most flashing is a straight length. This module covers the pieces that are not: cones and frustums such as pipe collars and funnels, transitions such as a square to round, unequal-width and peak miters, crickets, and radius coping.

It covers how each is laid out, joined, specified, installed and inspected.

Sources

Pattern Development: Sheet Metal Level 1 - Radial Line, Triangulation and Parallel Line parts (2021, CC BY 4.0) - BCcampus (Brian Coey)
PAC-Continuous Cleat Coping: Standard Accessories (DWG 41011-38588 Rev A, 06/06/22) - Petersen Aluminum Corporation (PAC-CLAD)
2021 Seattle Residential Code, Chapter 9 Roof Assemblies (IRC-based), R903.2.2 Crickets and saddles - City of Seattle, Department of Construction and Inspections

Glossary

Prism (parallel-line form): A sheet metal piece whose bends all run parallel and whose two ends are the same shape, such as any straight length of flashing formed on a folder.
Developable surface: A surface that can be laid out from a flat sheet: a ruled surface with zero Gaussian curvature everywhere, such as a cone, cylinder or plane.
Element line: A line on a sheet metal form that is projected into the pattern; in radial line development every element line radiates back to the radius point.
Radius point: The single point that every element line of a right cone radiates back to; the pattern arcs are swung from it.
Slant height: The outside edge of a cone from base to apex; in the elevation view it is always a true length, so it is the radius used for a radial line pattern.
Stretch-out arc: The arc a radial line pattern is laid out on, made equal in length to the circumference of the cone's base.
True length diagram (TLD): A 90 deg corner used in triangulation: the plan length of a line on one leg and the vertical height on the other give the line's true length on the hypotenuse.
Cricket (saddle): A raised construction on the ridge side of a chimney or roof penetration that diverts water around it; its covering is sheet metal or the roof covering.