Steel Decking for Concrete: Types and Uses

Walk through the framing of almost any modern office building, parking structure, or steel-framed mezzanine and you will find the floors built the same way: corrugated metal sheets first, wet concrete on top. Steel decking for concrete is the corrugated galvanized sheet that serves as permanent formwork and, in many cases, as structural reinforcement for the slab poured over it. If you are adding a mezzanine to a shop, framing a steel-joist floor, or just trying to understand a set of structural drawings, knowing the deck types, profiles, and gauges keeps you from ordering the wrong product. This guide breaks down how it works.

Why Pour Concrete on Steel Deck

The deck does two jobs. First, it is a stay-in-place form, so you skip building and stripping plywood formwork under the entire floor. You lay the sheets across the beams or joists, weld or fasten them down, and pour directly on top. Second, with the right profile, the deck becomes part of the finished slab’s strength rather than just a form you leave behind.

That combination is why steel-framed construction is fast. A crew can lay deck across a bay in a fraction of the time formwork would take, and the deck gives workers a safe platform to walk before the pour.

Composite Deck vs Form Deck

The single most important distinction is composite versus non-composite, because it changes how the floor is engineered.

• Composite deck has embossments, small dimples rolled into the flutes, that grip the cured concrete. The steel then acts as the bottom tension reinforcement, working together with the slab as one structural unit. This is the standard for elevated floors in commercial buildings.
• Form deck is non-composite. It is smooth and serves only as a form; the concrete slab must be reinforced separately with rebar or welded wire mesh. Form deck shows up under slabs where the deck is not counted on for strength, and thinner form profiles double as roof deck.

Get this wrong and you either overbuild or, far worse, under-reinforce. Always match the deck the engineer specified, not the closest thing the supplier has in stock.

Common Profiles: B-Deck, N-Deck, and Composite Deck

Profiles are named by their rib depth and shape. A few you will see constantly:

• 1.5-inch composite deck (often called 1.5 CD or by trade names like Lok-Floor) is the workhorse for elevated composite floors, spanning typical joist and beam layouts.
• 2-inch and 3-inch composite deck carry heavier loads and span farther, letting you space supporting steel wider.
• B-deck is a 1.5-inch roof and form profile, wide-rib, used as a form for lighter slabs and very commonly as roof deck.
• N-deck is a deep 3-inch profile for long spans where you want to minimize supporting steel.

Deeper ribs span farther and carry more, but they also raise the total floor thickness and use more concrete in the flutes. The engineer balances span, load, and floor depth to pick the profile.

Understanding Gauges

Steel deck is sold by gauge, and lower numbers mean thicker steel. The common range for floor and form deck is 22, 20, 18, and 16 gauge. A 22-gauge sheet is roughly 0.0295 inches thick; 16 gauge is about 0.0598 inches, more than twice as stout. Thicker gauge lets the deck span farther between supports and carry more construction load before the pour, but it costs more and weighs more to handle.

On a light residential mezzanine you might see 22 or 20 gauge over closely spaced joists. On a heavily loaded commercial floor with wide beam spacing, 18 or 16 gauge earns its keep. The gauge is always paired with a span rating in the load tables, so read both together.

Shear Studs and Composite Action

On an elevated composite floor, the steel deck helps the slab, but the whole floor also has to work with the steel beams underneath. That connection is made with shear studs, short steel pins welded through the deck to the top flange of the beam before the pour. The studs lock the concrete slab to the beam so they bend as one composite member, which is dramatically stiffer and stronger than a bare beam plus a loose slab.

Stud spacing and count come straight off the structural drawings. The welding is done with a stud gun that fuses each stud through the deck and into the beam in a single arc, and inspectors bend-test a sample to confirm the welds took.

Where You’ll Use It

Steel deck over concrete is standard for commercial floors, mezzanines and equipment platforms, parking garages, stadium concourses, and any steel-framed multistory building. In residential and light-commercial work it shows up when someone builds a floor over steel joists, a rooftop deck slab, or an interior mezzanine in a shop or warehouse. It also serves as the form under some slab-on-metal-frame additions and porches where wood framing does not suit the loads or the fire rating.

What ties all these uses together is a supporting steel structure. Steel deck is not laid on soil like a slab-on-grade; it always spans between joists, beams, or bearing walls.

Spans, Loads, and Reading the Tables

Every deck profile comes with a manufacturer load table, and learning to read it saves you from guesswork. The table lists the deck by profile and gauge down one axis and the clear span between supports across the other, then gives the total load the deck can carry and, on composite deck, the slab depth and reinforcing that goes with it. A 1.5-inch composite deck in 20 gauge might span 8 to 10 feet between beams under a normal office floor load, while the same profile in 16 gauge spans farther or carries more.

Two loads matter. The construction load is what the bare deck holds during the pour, including workers, the concrete buggy, and the wet concrete itself before it cures. The service load is what the finished composite floor carries in use. Deck that is fine once the slab cures can still fail during the pour if the span is too long for the bare-deck rating, which is why temporary shoring is sometimes added mid-span on long runs.

Fastening and Detailing the Deck

Laying deck is not just dropping sheets. Each sheet is fastened to the supporting steel at every bearing point, either with puddle welds burned through the deck into the beam flange or with self-drilling structural screws and powder-actuated pins on lighter work. The side laps between adjacent sheets are stitched together with screws or button-punched so the panels act as one diaphragm, which also braces the whole frame against lateral loads like wind and seismic.

Edges, openings, and pour stops need detailing too. A bent steel pour stop or edge angle dams the wet concrete at the slab perimeter and at stair and duct openings. Miss those and the pour runs off the edge of the deck. Reinforcing mesh or rebar rides on chairs above the deck for crack control, and on composite floors the shear studs are already welded before any concrete arrives.

What Steel Decking for Concrete Costs

Material pricing swings with the steel market, but a workable planning range for the deck alone is roughly $2 to $6 per square foot depending on profile, gauge, and galvanizing. Add the concrete, reinforcing, shear studs, and labor, and an installed composite floor system commonly lands somewhere near $10 to $20 per square foot. Deeper profiles and heavier gauges push the top of that range, while a light form deck under a lightly reinforced slab sits near the bottom.

Galvanizing matters for cost and durability. A G60 or G90 zinc coating resists corrosion in normal interior floors; more aggressive or exposed environments call for heavier coatings or painted deck, which add to the price. Waste and delivery add up too: deck ships in bundles cut to length, and long or oddly shaped bays generate offcuts you pay for whether you use them or not.

Do not forget the concrete volume hidden in the flutes. A deep composite profile carries more concrete in its ribs than a flat form, so your yardage and your dead load both climb with rib depth. On a large floor that difference shows up as real dollars and real weight the supporting steel has to carry.

Getting It Right

The theme running through every one of these decisions is that steel decking for concrete is an engineered system, not a commodity you grab off a rack. Composite or form, the profile, the gauge, the span, and the shear studs are all specified together for a reason. Order what the drawings call out, fasten it per the plan, and let the deck do what it does best: form the slab, reinforce it, and get your floor built fast.