Metal roofing has its own vocabulary, and bids are full of it. This glossary defines the terms you are most likely to meet in a quote, a warranty or a conversation with an installer, one sentence each, grouped A to Z. For the longer story behind a term, follow the links into the homeowner hub.
A
- Aluminum — A light roofing metal that does not rust, performs well near salt water and is usually painted; see the aluminum guide.
- Architectural panel — A metal panel made for a sloped roof over a solid deck, as opposed to a structural panel that spans open framing on its own.
- ASTM E1592 — A standard test that measures how much wind uplift pressure a metal roof panel system can take before it fails.
B
- Batten seam — A standing seam variant in which panels wrap over a raised wood or metal batten, giving a wide, flat-topped rib; see flat-lock and batten seam.
- Butyl tape — A sticky sealant tape placed inside seams and under flashings to make a long-lasting watertight joint.
C
- Class 4 — The highest impact rating under UL 2218, earned by surviving a 2-inch steel ball dropped from 20 feet without cracking; see the hail rating guide.
- Class A — The best fire rating for a roof covering under UL 790, which most metal roof assemblies achieve.
- Clip — A small metal piece that fastens a standing seam panel to the deck while staying hidden inside the seam.
- Closure — A foam or metal piece cut to the panel profile that seals the open ends of the ribs at the eave and ridge.
- Coil — The long roll of flat sheet metal that roll formers and brakes turn into panels and trim.
- Cool roof — A roof finish that reflects much of the sun’s energy and sheds absorbed heat quickly, lowering attic temperatures; see energy savings.
- Copper — A premium roofing metal that lasts a century or more and weathers from brown to green; see the copper guide.
- Corrugated — A wavy panel profile, one of the oldest metal roofing shapes, usually installed with exposed fasteners.
- Cricket — A small peaked saddle built behind a chimney or above a wall to divert water around it.
D
- Deck — The wood or metal surface the roof is attached to; most residential metal roofs go over solid plywood or OSB decking.
- Drip edge — Metal trim at the eave and rake that directs water off the edge and into the gutter instead of behind the fascia.
- Double lock — A mechanically seamed standing seam joint folded twice, to 180 degrees, for the most watertight seam, used on low slopes.
E
- Eave — The lower horizontal edge of a roof, where the gutter usually hangs.
- Expansion and contraction — The daily movement of metal as it heats and cools, which clip design and panel length have to allow for.
- Exposed fastener — A panel system in which screws go through the face of the panel into the deck or purlins, with a washer sealing each hole; see the exposed fastener guide.
F
- Flashing — Shaped metal pieces that keep water out where the roof meets walls, chimneys, pipes, valleys and edges.
- Flat-lock — A system of small flat panels hooked together on all four sides and soldered or sealed, used on low slopes, curves and historic buildings.
- Floating clip — A panel clip with a sliding part that lets long standing seam panels expand and contract without buckling; a fixed clip holds the panel still.
G
- Gable — The triangular wall section under the end of a pitched roof; a gable roof has two sloped sides and two gable ends.
- Galvalume — Steel coated with an alloy of about 55 percent aluminum and the rest mostly zinc, the standard base for painted steel roofing; see Galvalume vs galvanized.
- Galvanized — Steel coated in zinc alone, with G90 a common coating weight, used for trim, agricultural panels and some painted roofing.
- Gauge — The thickness number for steel sheet, where a lower number means thicker metal, so 24 gauge is heavier than 26 or 29; see gauge explained.
H
- Hem — A folded edge on a panel or trim piece that stiffens it, hides the raw cut and often hooks onto a cleat.
- High-temperature underlayment — Underlayment rated for the hotter deck temperatures under metal, often self-adhered, that will not soften or stick to the panels.
- Hip — The sloped outside corner where two roof planes meet, covered with a hip cap.
I
- Ice and water shield — A self-adhered rubberized membrane applied at eaves, valleys and penetrations to stop leaks from ice dams and wind-driven rain.
- Ice dam — A ridge of ice at the eave that traps meltwater and pushes it under the roofing.
K
- Kynar 500 — A trade name for the PVDF resin used in premium metal roof paint; Hylar 5000 is the other common name for the same chemistry.
L
- Lock — The folded joint along the edge of a standing seam panel that connects it to the next panel, either snapped or mechanically seamed.
M
- Mechanical lock — A standing seam system in which a hand or electric seamer folds the panel edges together after the panels are clipped down; see snap-lock vs mechanical lock.
- Metal shingles — Small stamped metal pieces shaped like shingles, shakes, slate or tile, installed in interlocking courses; see the metal shingles guide.
- Mil — One thousandth of an inch, used to describe paint film thickness and sometimes sheet thickness.
O
- Oil canning — Visible waviness in the flat areas of metal panels, a normal cosmetic effect that striations, narrower pans and thicker metal reduce.
- Open framing — Purlins or battens with no solid deck beneath, common on agricultural and some commercial buildings.
P
- Pan — The flat part of a standing seam panel between the seams.
- Panel profile — The cross-section shape of a panel: seam height, pan width, ribs and striations; see panel profiles explained.
- Patina — The surface layer that forms as copper or zinc weathers, protecting the metal and changing its color.
- Pitch — The steepness of a roof, written as inches of rise per 12 inches of run, such as 4:12.
- Purlin — A horizontal framing member that panels fasten to on open-framed buildings.
- PVDF — Polyvinylidene fluoride, the premium paint resin for metal roofing, with the best resistance to fading and chalking; see PVDF vs SMP.
R
- Rake — The sloped edge of a roof at a gable end, finished with rake trim.
- Ridge — The horizontal peak where two roof planes meet, covered with a ridge cap and often vented.
- Roll former — The machine that shapes flat coil into finished panels, either in a shop or on a trailer at the job site.
- R-panel — A common exposed fastener profile for commercial and agricultural buildings, with trapezoid ribs about 12 inches apart.
S
- Seam — The joint between two panels; in standing seam roofing it stands up above the water line.
- Seamer — A hand or electric tool that folds a mechanical lock seam closed after the panels are installed.
- SMP — Silicone-modified polyester, a mid-grade paint system common on agricultural and budget panels.
- Snap-lock — A standing seam system in which the panel edges snap together by hand without a seaming tool, suited to steeper slopes.
- Snow guard — A bracket or rail that holds snow on the roof so it melts gradually instead of sliding off in a sheet; see snow retention and gutters.
- Square — The roofing unit of area, 100 square feet; prices are often quoted per square.
- Standing seam — A roof of long vertical panels joined by raised seams with hidden fasteners; see the standing seam guide.
- Stone-coated steel — Steel panels shaped like shingles, shakes or tile and coated with stone granules set in acrylic; see the stone-coated steel guide.
- Striations — Shallow lines pressed into a panel’s pan to stiffen it and hide oil canning.
- Substrate — The base metal under the paint, such as Galvalume steel or aluminum.
T
- Tear-off — Removing the old roofing down to the deck before the new roof goes on, as opposed to a roof-over; see metal roof over shingles.
- Trim — All the shaped metal pieces besides the panels: ridge, hip, eave, rake, valley, wall and transition pieces.
U
- UL 2218 — The impact test standard for roofing materials; Class 4 is the top rating.
- UL 790 — The fire test standard for roof coverings; Class A is the top rating.
- Underlayment — The water-resistant layer between the deck and the panels, synthetic or self-adhered; see underlayment and ventilation.
- Uplift — The force of wind trying to pull the roof off the building, which clip spacing and fastening are engineered to resist; see metal roofs and wind.
V
- Valley — The inside corner where two roof planes meet and water collects, lined with valley flashing.
- Verdigris — The green patina that forms on copper after years of weathering.
W
- Weathertightness warranty — A manufacturer’s warranty, usually on commercial jobs, that covers leaks when an approved installer uses the complete system; see warranties explained.
- Workmanship warranty — The installer’s own promise to fix installation errors for a set period, separate from the material and paint warranties.
Z
- Zinc — A soft, long-lived roofing metal that forms a blue-gray patina able to cover its own scratches; see the zinc guide.
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