Metal Deck Takeoff: Gauges and Profiles
A metal deck takeoff comes down to four numbers per deck type: square footage (gross area plus laps and waste), profile (1½" B, 3" N, or composite floor deck), gauge (22, 20, 18, or 16), and finish (painted or galvanized, G60/G90). Get those four right for each roof and floor area on the plans, then add the accessories — closures, pour stops, edge form, fasteners, and studs — and you have a complete deck package. Most deck busts don't come from the area math; they come from missing a gauge change between areas or forgetting the accessories entirely.
Deck is the simplest line in a structural steel bid and the one estimators treat most carelessly, because "it's just square footage." On a 60,000 SF warehouse roof, the difference between 22 and 20 gauge B deck is roughly 10 tons of steel. Bid the wrong gauge and you eat it.
What gauges does steel deck come in — and what do they weigh?
Steel deck is rolled from sheet in standard gauges: 22, 20, 18, and 16, from thinnest to heaviest. Remember that gauge numbers run backwards — 16 gauge is roughly twice the steel of 22 gauge.
| Gauge | Design thickness | 1½" Type B roof deck (psf) | 3" Type N roof deck (psf) | 2" composite floor deck (psf, deck only) |
|---|---|---|---|---|
| 22 | 0.0295" | ~1.6 | ~2.0 | ~1.7 |
| 20 | 0.0358" | ~2.0 | ~2.4 | ~2.1 |
| 18 | 0.0474" | ~2.6 | ~3.2 | ~2.8 |
| 16 | 0.0598" | ~3.3 | ~4.0 | ~3.5 |
Weights vary slightly by manufacturer (Vulcraft, New Millennium, Canam, ASC all publish tables), so use the catalog for the basis-of-design product when the spec names one; for budget pricing the table above is close enough. Note that composite floor deck weight is the deck only — concrete adds 30–75 psf depending on slab depth and normal vs. lightweight, but that's the concrete sub's problem, not yours.
Gauge is driven by span, uplift, and diaphragm shear. 22 gauge B deck handles spans to about 5'–6' — joists at 5' on center is why 22 ga is the default warehouse roof — while wider spacing pushes you to 20 or 18 gauge. You don't pick the gauge, the EOR does, but knowing the logic helps you catch a plan/spec conflict before it costs you.
What's the difference between roof deck and composite floor deck?
Roof deck is a bare structural panel: it spans between joists or purlins and carries roofing loads. Composite floor deck is a stay-in-place concrete form with embossments (dimples) rolled into the webs so the cured slab and the deck act together as a composite section.
| Property | Type B roof deck | Type N roof deck | Composite floor deck (VL/LOK types) |
|---|---|---|---|
| Depth | 1½" | 3" | 1½", 2", or 3" |
| Typical spans | 4'–7' | 8'–15' | 8'–12' (with shoring, more) |
| Coverage width | 36" | 24" | 36" (2"), 24"–36" (3") |
| Rib type | Wide rib | Deep rib | Embossed webs for concrete bond |
| Finish | Painted (interior) or galvanized | Painted or galvanized | Galvanized almost always (G60 min) |
| Typical use | Warehouse/big-box roofs on joists | Long spans, canopies, wide bay roofs | Elevated slabs in multi-story buildings |
A few practical notes:
- Type B is the workhorse — probably 80% of the roof deck you'll ever take off. Type A (narrow rib) and F (intermediate rib) still exist but mostly show up on reroof/renovation jobs matching existing deck.
- Type N costs more per square foot and comes in narrower sheets, so your sheet count per square is higher. Don't price N deck areas at your B deck number.
- Acoustic deck (perforated webs with fiberglass batts) shows up on gyms and auditoriums and can run double the price of plain B deck — flag "acoustical" in the deck note immediately.
- Form deck (9/16" to 1 5/16" shallow, non-composite, 26–28 gauge) is a different, cheaper animal. Don't confuse it with composite deck.
If the job is a typical warehouse or industrial building, expect B deck on joists at the roof and no floor deck at all. Multi-story office and mixed-use is where composite deck and studs enter the bid.
How do you read deck callouts and span direction on framing plans?
Deck shows up on framing plans three ways, and you need all three:
- The deck note or legend. Something like:
1½" x 22 GA. TYPE B ROOF DECK, GALV. G60, 36/4 ATTACHMENT W/ #10 SIDELAP SCREWS @ 24" O.C.That one line gives you profile, gauge, finish, and the fastening pattern (36/4 = every rib at 36" sheet width, 4 fasteners per sheet per support). - Hatched areas or area tags. Larger jobs split the roof into deck zones — heavier gauge or tighter fastening at the perimeter and corners for wind uplift, lighter in the field. Each zone is a separate takeoff line. Missing a perimeter zone that's 18 ga while the field is 22 ga is a classic bust.
- Span direction arrows. The double-headed arrow (or "DECK SPAN" symbol) tells you which way the sheets run — always perpendicular to the joists or beams supporting them. Span direction determines your sheet lengths, end lap count, and how much cutting happens at skewed grid lines.
Also check the general notes and spec section 05 31 00 for: minimum bearing (typically 1½"–2" on steel), end lap requirement (2" minimum over supports is standard), attachment method (puddle welds with weld washers on thin gauge, powder-actuated pins, or screws), and whether sidelaps are button-punched, screwed, or welded. Welded attachment vs. screwed changes your labor number meaningfully.
How do you calculate deck square footage — laps, openings, and waste?
The math itself is simple; the discipline is in the deductions and adds.
Step 1 — gross area by zone. Multiply bay dimensions off the grid lines for each area with the same profile/gauge/finish. Keep roof and each floor level separate.
Step 2 — openings. The common rule: deduct openings larger than about 16–25 SF (large RTU openings, stair and elevator shafts, skylight banks). Don't deduct small openings — you buy the full sheet anyway and cut the hole in the field. The cut-out is waste, not savings.
Step 3 — laps. End laps consume material: a 2" lap at every end joint adds roughly 1% on typical sheet lengths. Sidelaps are built into the published coverage width (a "36-inch" sheet is 36" coverage, not 36" of flat steel), so don't add for them.
Step 4 — waste. Add 5% on clean rectangular buildings, 7–10% on jobs with skewed grids, radiused edges, or lots of small roof areas. Deck ships cut-to-length, so drop is lower than on beams — but every hip, valley, and skew generates triangle offcuts you can't reuse. Same logic as waste factors for steel fabrication, applied to sheet instead of bar stock.
Worked example: 200' x 300' warehouse roof, B deck, two RTU openings at 8' x 12'.
- Gross: 200 x 300 = 60,000 SF
- Openings: 2 x 96 SF = 192 SF — under a typical deduction threshold on a job this size; leave it
- End laps: +1% = 600 SF
- Waste: +5% = 3,000 SF
- Order quantity: ~63,600 SF. At 22 ga (~1.6 psf) that's about 51 tons of deck.
Which deck accessories get missed in takeoffs?
Accessories run 10–20% of the deck package value and they're the most-missed items in deck bids:
- Pour stops (screed angles). Bent-plate edge forms at every slab edge on composite floors. Taken off by the linear foot, sized by slab overhang and depth — these get heavy (12 ga down to 3/16" plate) and they add up fast on a building with lots of edge.
- Closures. Rubber or foam closure strips where deck flutes hit walls and beams, metal closures (cell closures, zee closures) at slab edges and deck direction changes. Linear-foot items, cheap per foot, everywhere on the job.
- Ridge and valley plates, transition sheets on sloped roofs.
- Sump pans at roof drains — each one is a fabricated item.
- Shear studs. ¾" diameter headed studs welded through composite deck to the beam flange. Count them off the framing plan — stud counts are called out per beam ("24 STUDS" beside the member). On a mid-rise office job the stud count runs into five figures; whoever bids them needs the count.
- Fasteners and welding. Powder-actuated pins, #10/#12 sidelap screws, weld washers. Usually priced into erection labor, but the pattern (36/4 vs 36/7, sidelap spacing) drives that labor.
- Touch-up. Galvanizing repair paint at welds is spec'd on nearly every job and priced on almost none.
Run these against your commercial takeoff checklist the same way you'd verify base plates and anchor bolts — the small stuff is where deck bids leak money.
Who bids the deck: fabricator, erector, or specialty sub?
It varies by region and contract structure, which is exactly why deck gets double-bid or missed entirely:
- Supply: Deck usually comes from a deck/joist manufacturer (Vulcraft, New Millennium, Canam, ASC), not the fabricator's shop. The structural steel fabricator often carries it as a buyout when the steel package is "furnish and install structural steel, joists, and deck."
- Installation: The steel erector typically installs deck when it rides with the steel package. In some markets, dedicated deck subs handle install — especially on decks with heavy welding requirements or big composite floor jobs.
- Shear studs: Almost always a specialty sub with automatic stud-welding equipment, contracted by either the erector or the GC. If you're the fabricator, make sure your quote says whether studs are in or out — a five-figure stud count is a bad thing to discover you own.
- Concrete on deck is the concrete contractor. Pour stops sit right on the boundary — spec section says metal deck, concrete guys assume steel has it, steel assumes concrete. Read the scope letter twice.
The takeoff itself is the same regardless of who owns the scope: someone has to count square feet by profile and gauge, and everyone in the chain checks everyone else's number. Deck areas pair naturally with the joist count above them — if you're doing one, you're doing both, and the bar joist takeoff uses the same framing plan you already have open. SteelFlo's AI detection handles the framing members on those same plans — beams, joists, angles, and 4,500+ sections across 6 standards — with 95-99% accuracy after human verification, so the member takeoff is done while you focus the manual effort on deck areas and accessories.
Get the framing takeoff done while you do the deck
Deck squares and accessories still take an estimator's eye. The hundreds of beam and joist labels on the same drawings don't. Upload the framing plans, let the AI box every steel member on every sheet, verify the results, and export your BOM — then spend your time on the deck zones, pour stops, and scope-letter language where judgment actually pays. Start 3 free takeoffs — no credit card required.