Architectural Flashing Supply
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Flashing geometry and movement accommodation · Lesson 1 of 4

Flashing geometry and movement accommodation: principles and terminology

What makes a flashing run move, which decisions the drawings make about it, where a run is held, what restrains it and how lengths are joined, with the roof safety rule that applies on a site visit.

You will be able to: Define design temperature range, fixed point, sliding clip, restraint and the main ways lengths are joined, and name the decisions in the drawings that give a flashing run room to move.

12 min · 12 slides · 9 questions

All lessons in this module
Slide 1 of 12

Four decisions the drawings make

A flashing run changes length with temperature; the drawings decide the room it has.

Course framing: four decisions sit with the drawings. They are the design temperature range, the fixed point, the joint family and the geometry that gives each joint its travel.

AFS's thermal method says joint spacing and clip design take validated design rules and the engineer of record.

Four movement decisions made in the drawingsFour cards: the design temperature range, the fixed point, the joint family and the joint geometry, each with who decides it, above the movement formula dL equals alpha times L times dT.Four movement decisionsRangeMetal surface range,with its sourcewho: designer of recordFixed pointOne point per piece,between movement jointswho: designer and makerJoint familyLap, or a gap witha splice platewho: designer of recordJoint geometryRoom to close andopen on install daywho: designer; AFS checks fitMovement: dL = alpha x L x dT

Four cards: the design temperature range, the fixed point, the joint family and the joint geometry, each with who decides it, above the movement formula dL equals alpha times L times dT.

The four decisions this module teaches, with the movement formula underneath. The who lines are course framing: the designer of record decides, and AFS checks fit against its limits.

Sources

Videos for this lesson

What this video shows: The channel's description says it explains what standing seam clips are, the types available and their uses, and that the wrong clip could void the engineering. It is a supplier's reference video; follow the panel maker for the system.

Video: Which Metal Roofing Clip Should You Choose? Types, Uses, Installation by The Metal Roofing Channel, on YouTube. Chosen from the video's published description.

Glossary

Design temperature range
The span of metal surface temperatures a project chooses to design movement for; VA and the University of Houston each print their own in their specifications.
Fixed point
The place where a panel or run is held to the structure; movement is measured away from it, and NRCA says it should be a horizontal point shared by all panels.
Sliding clip
A two- or three-piece clip of the kind NRCA says long panels use, which lets the panel move; short panels usually use one-piece clips that roll and flex instead.
Restraint
Anything that stops a roof edge component from expanding and contracting freely, such as a tight crimp on a cleat or an attached appliance.
Splice plate
A plate that bridges a gap between lineal sections to prevent water infiltration while the sections move.
Thermal movement
The change in length of a metal run as its temperature changes, worked in AFS's thermal method as dL = alpha x L x dT.