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Metal roofs, walls and rainscreens · Lesson 1 of 4

Metal roofs, walls and rainscreens: principles and terminology

Structural and non-structural panels, water-shedding and water-barrier panels, standing seam and through-fastened attachment, metal veneer and MCM, rainscreen walls, and what AFS makes within that picture.

You will be able to: Classify a metal roof or wall by span, water strategy and attachment, define the terms of panel types and rainscreen walls, say where AFS fits, and state the safety boundary for observing roof work.

11 min · 12 slides · 8 questions

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Slide 1 of 12

Three questions that classify a system

Three questions classify a metal system: does the panel span open framing or need a deck, does it shed water or hold water out, and how is it attached.

The next slides take each question in turn, then look at walls.

Three questions that classify a metal roof or wallThree question panels with section sketches: structural panel on purlins versus non-structural panel on a solid deck with underlayment; a steep slope that sheds water versus a low slope with a sealed seam that holds water out; a concealed clip at a standing seam versus an exposed fastener with a washer. A fourth panel shows two rainscreen walls in section: drained and back-ventilated, and pressure-equalized with a compartment seal across the cavity.Three questions thatclassify a metal roof or wallDoes the panel span?ABStructural: spansopen framingECDNon-structural:needs a deckDoes it shed water or hold it out?Sheds water:steeper slopesHolds water out:sealed, low slopeHow is it attached?FConcealed clipat the seamGExposed fastenerwith washerRainscreen walls, in sectionHJKLMDrained andback-ventilatedPressure-equalized

Four panels. Does the panel span: a structural panel on open purlins against a non-structural panel on a solid deck with underlayment. Shed or hold water: a steep roof that sheds water against a low sealed roof that holds water out. How attached: a concealed clip at a seam against an exposed fastener with a washer. Rainscreen walls in section: a drained and back-ventilated wall, and a pressure-equalized wall with a compartment seal across the cavity.

A
Purlin (open framing)
B
Structural panel, spanning between purlins
C
Solid deck
D
Underlayment
E
Non-structural panel on the deck
F
Concealed clip at the seam
G
Exposed fastener with washer
H
Cladding, with open joints
J
Cavity
K
Air/water barrier
L
Sheathing
M
Compartment seal (air dam) across the cavity
Classification as MCA and the IBC describe it, drawn as simple sections, not to scale. Metal panels and cladding are teal; other layers are charcoal outline and steel blue. Arrows on the sheds-water sketch show runoff down the slope.

Sources

Videos for this lesson

What this video shows: A Sheffield Metals technical Q&A on open framing, the difference between architectural and structural panels, and testing methods for open framing. One supplier's view; the maker's published details govern. Checked against the video's description.

Video: Open Framing Metal Roof Applications: Structural vs. Architectural by The Metal Roofing Channel, on YouTube. Chosen from the video's published description.

What this video shows: One wall panel maker explains judging a wall panel by its joinery, and how horizontal joints address the forces that drive water into a wall. One maker's system. Checked against the video's description.

Video: CENTRIA I The Rainscreen Principle of Performance by CENTRIA, on YouTube. Chosen from the video's published description.

Glossary

Structural panel
A metal roof panel that carries roof loads and spans open areas, getting its strength from formed ribs, so it normally needs no solid substrate (MCA).
Non-structural (architectural) panel
A metal roof panel that mainly gives appearance and weather protection and needs a solid deck or closely spaced supports (MCA).
Hydrokinetic panel
A water-shedding metal roof panel. MCA says it performs best on steeper roofs and notes that the minimum slope is often set by the panel manufacturer.
Hydrostatic panel
A water-barrier metal roof panel that resists slow-moving water at low slopes, using more sealant, gaskets and fasteners (MCA).
Standing seam
A metal roof seam where the panel edges are turned up and folded so the seam stands up above the roof, closed by a seaming machine, a snap cap or an integral lock (MCA).
Through-fastened panel
A metal panel attached with threaded fasteners and washers that stay visible; MCA notes thermal movement can limit its length.
Rainscreen wall
In MCA's description, a wall of two components, a cladding assembly and an air/water barrier on the sheathing, with a cavity between them.
Drained and back-ventilated (D/BV) rainscreen
A rainscreen whose open joints admit water and whose cavity drains and dries it; the air/water barrier behind is designed to be exposed to water (MCA).
Pressure-equalized rainscreen (PER)
A rainscreen with a compartmentalised cavity, tested to AAMA 508; MCA calls the name a bit of a misnomer and notes that designers are beginning to gravitate toward "pressure moderated".