Hems, returns, locks and seams · Lesson 1 of 4

Hems, returns, locks and seams: principles and terminology

What hems and locks are for, the three hems FlashDraft draws and which face they fold to, the seam families that join sheets, and the hazards at the edge.

You will be able to: Define hem, return, lock and seam, name the three AFS hems and the main seam families, and state where the safety limits are.

10 min · 11 slides · 8 questions

All lessons in this module

Slide 1 of 11

Hems, returns, locks and seams

A hem is a 180 deg fold at the end of a leg; the part folded back is the return.

Its length, the return, is what AFS checks against its minimum.

A lock interlocks the edges of two sheets. A seam is the finished joint between them: locked, lapped, soldered or riveted.

Sources

FlashDraft hem types and starting dimensions - Architectural Flashing Supply
AFS fabrication limits - materials, thicknesses, bend rules and sizes the shop can make - Architectural Flashing Supply
Copper in Architecture Design Handbook - 7.2 Joints and Seams - Copper Development Association

Videos for this lesson

What this video shows: The Copper Development Association shows a double-lock standing seam made with a seaming anvil and hammer, and names the tools.

Video: How-To: Standing Seam by Copper Development Association, on YouTube. Chosen from the video's published description.

Glossary

Hem: A 180 deg fold at the end of a leg that stiffens and finishes the edge.
Return: The folded-back part of a hem; its length is what AFS checks against its minimum.
Kick (hem face): Which face of the sheet a hem folds to: the inside face, the one the profile curls toward, or the outside face.
Single lock: One interlocking fold between two sheet edges; in roof seaming, the first 90 deg of motion.
Double lock: A single lock with an additional fold; in roof seaming, a further 90 deg of motion.
Point of operation: In OSHA's words, the area on a machine where work is actually performed upon the material.