Construction glossary · Steel and structural
What is metal decking in construction?
Metal decking is corrugated steel sheet installed over steel framing to form the structural surface of a roof or floor. Commercial jobs use two main types: Type B 1.5 inch roof deck in 20 to 22 gauge, and 2 or 3 inch composite floor deck that acts together with its concrete fill. Estimators take it off in square feet from the framing plans and add 5 to 10 percent for laps and waste.
Updated June 2026 · Reviewed by the Ruh construction team
Composite metal deck section
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Book a walkthroughMetal decking is the corrugated steel sheet that spans between joists, beams, and purlins to create the working surface of a roof or floor. On commercial work you will see two flavors: Type B 1.5 inch roof deck, usually 20 or 22 gauge, that carries rigid insulation and the roofing membrane, and composite floor deck, 2 or 3 inch deep, whose embossed profile locks into the concrete fill so deck and slab act as one structural unit. Deck appears on the structural framing plans, with profile, gauge, finish, and attachment called out in the deck schedule and general notes. A deck supplier or the steel fabricator furnishes it, the steel erector or a decking sub installs it, and the GC estimator sanity checks the square footage against the building footprint. New estimators routinely make three mistakes: pulling area from architectural roof plans instead of structural framing plans, skipping the lap and waste allowance, and pricing every area at one rate when gauge and finish, galvanized versus painted, move the unit price meaningfully.
Deck is taken off and priced in square feet (sf), measured from the structural framing plans rather than the architectural sheets. Measure each profile and gauge as its own quantity, because Type B roof deck and composite floor deck carry different supplied and installed rates. Deduct large openings such as stair and elevator shafts, but small mechanical penetrations are usually left in as waste. Then add 5 to 10 percent for end laps, side laps, and cutting waste, with the high end reserved for cut-up roofs with skews and many openings. In the estimate, deck lands as a supplied and installed sf line under the structural steel division, with puddle welds or screws either inside the unit rate or broken out as attachment.
Worked example
Take a single story warehouse roof framed 200 ft x 150 ft with Type B 1.5 inch, 22 gauge galvanized deck. Step 1, gross area: 200 ft x 150 ft = 30,000 sf. Step 2, deduct large openings: two RTU wells at 10 ft x 12 ft = 120 sf each, so 2 x 120 sf = 240 sf, and 30,000 sf - 240 sf = 29,760 sf neat. Step 3, add laps and waste at 7 percent for a simple rectangular roof: 29,760 sf x 1.07 = 31,843.2 sf, carried as 31,850 sf. Step 4, price it: at an illustrative supplied and installed rate of $4.25 per sf for this gauge and finish, 31,850 sf x $4.25 = $135,362.50, carried as $135,400. If the spec bumps the deck to 20 gauge or switches areas to composite floor deck with concrete fill, the rate changes, so keep each profile and gauge on its own line.
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How Ruh handles metal decking
Ruh takes deck off straight from the contractor's framing plans, measuring each profile and gauge as its own square foot quantity with the lap and waste factor applied in the open. It then prices those quantities against the contractor's own price book, using their real supplied and installed rates for each gauge and finish. The estimator reviews the measured areas and allowances and signs off before the line goes into the bid.
See construction estimating softwareMetal decking: frequently asked questions
What is the difference between Type B roof deck and composite floor deck?+
Type B is a 1.5 inch deep roof profile, typically 20 or 22 gauge, that simply spans between joists and carries insulation and roofing; the deck alone is the structure. Composite floor deck is 2 or 3 inch deep with embossments rolled into the webs that bond with the concrete fill, so the deck works as positive reinforcement for the slab. They are taken off separately because the profiles, gauges, and unit prices are different, and composite areas also bring concrete, mesh or rebar, and often shear studs into scope.
How much should I add to a metal deck takeoff for laps and waste?+
Most estimators carry 5 to 10 percent on top of the neat framing area. End laps over supports, side laps between sheets, and cutting at openings and skewed edges all consume material that never shows up in the plan dimensions. A clean rectangular roof can sit near 5 percent, while a cut-up roof with hips, multiple levels, or many penetrations earns the 10 percent end. Keep the neat quantity and the factor visible as separate numbers so the math can be defended at bid review.
Does gauge or finish matter more to deck pricing?+
Both move the number, which is why they have to be read off the deck schedule before pricing. Stepping from 22 gauge to 20 or 18 gauge adds real steel weight per sf, and galvanized deck costs more than painted or prime coated deck of the same gauge. Attachment is the other swing item: puddle welds, screws, and side lap fasteners may be inside the installed rate or priced separately, and shear studs on composite beams are almost always their own line.
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Figures on this page are illustrative. Construction estimates depend on project-specific conditions, source documents, market pricing, and professional judgment. Ruh's AI assists the estimator and does not replace professional review: your team reviews, validates, and approves every estimate, bid, and pricing decision.