What is metal decking in construction?

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.

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.

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.