On a commercial wall-and-ceiling bid the ceiling is often two trades wearing one company name. ACT (acoustical ceiling tile — grid and lay-in) is not a gypsum ceiling with a different finish. Gypsum is hang, tape, and a GA-214 level. Between them sits drywall-suspension: steel tees that take board, not tile.
This page is takeoff language for the drywall sub that sells all three — or that needs to exclude the one it does not. It is not a homeowner ceiling guide and not a reprint of CISCA or a mill catalog. Spec documents to have on the desk: ASTM C635 (suspension-system manufacture) and ASTM C636 (installation) for ACT; ASTM E580 and the IBC seismic design category for seismic restraint; ASTM C840 / GA-216 for gypsum application; the ceiling manufacturer’s catalog (USG and peers) for the named grid and tile.
Residential production rarely bids ACT. A house ceiling is gypsum. Keep those crews out of this number unless the shop actually sells grid.
Three ceilings, three rulesets
ACT — lay-in acoustical. Main tees, cross tees, wall angle or shadow mold, hanger wire, tile. Accessible plenum. The tile is the finish. Movement, seismic clips, compression posts, and splay wires live in C636 / E580 / CISCA language, not in gypsum control-joint language. Directory term: Acoustical ceilings (ACT).
Gypsum, direct-applied. Board screwed to joists, cold-rolled channel and hat furring, or resilient channel. Fastener class and spacing are C840 / GA-216 and the listed fire design — see how to hang drywall. Finish is a level, not a tile. Control joints follow the GA-216 ceiling table (30-foot / 900 sf without perimeter relief; 50-foot / 2,500 sf with it, on interior ceilings).
Drywall-suspension (drywall grid). Main tees and cross tees made to take gypsum screws, hanger wire, wall angle or channel molding. Board is hung and finished like a gypsum ceiling. USG and other mills publish drywall-suspension catalogs that still cite C635 / C636 for the grid and C840 / C754 for the board. Seismic behavior is not identical to a lay-in ACT ceiling — screw-attached gypsum is a diaphragm; lay-in tile is not. Pull the mill’s seismic note for the system you are hanging, not the ACT one next to it on the reflected ceiling plan.
Do not price drywall-suspension as “ACT plus mud.” You just omitted hang, tape, finish level, and gypsum control joints.
What the documents are actually buying
Read the reflected ceiling plan and the spec section. A cloud of 2×2 tile in an open office is ACT. A smooth gypsum lid at the boardroom, a rated corridor membrane, a bulkhead, a soffit, and the gypsum wrap of a beam are not. The same sheet often has both, plus a note that says “gypsum at all bulkheads.” That note is where shops donate footage.
Fire. Rated floor-ceilings and roof-ceilings are listed assemblies (UL / GA-600). Tile in a grid is not a silent substitute for a gypsum membrane, and a gypsum lid is not a silent substitute for a listed acoustical fire panel. If the design names a product, that product is on the takeoff.
Access. ACT is how MEP stays reachable. Gypsum wants access panels wherever a valve or junction has to be reached later. If the drawing is silent, qualify: gypsum lids include no access panels unless shown.
Acoustics. NRC lives on the tile face; CAC / flanking lives in the plenum and the partition head. Gypsum lids with insulation are a different STC conversation. Do not copy an NRC from a tile data sheet onto a Level 4 gypsum ceiling.
Light and finish. ACT hides the plenum. Gypsum photographs every fastener in critical light. Level 4 vs Level 5 on a smooth gypsum ceiling is the same argument as the wall — finishing levels.
Moisture and kitchens. Kitchen, pool, and some healthcare rooms specify a tile or a gypsum product that can live there. Standard interior wallboard on a bathroom soffit is still the wrong SKU if the spec named MR or glass-mat.
Bid lines shops miss
On ACT, estimators who only hang board forget:
- Hanger wire gauge and spacing, including extra wires at fixtures, coves, and ramped soffits
- Wall angle vs shadow mold vs extrusion at gypsum bulkheads
- Seismic: category on the structural notes, stabilizer bars, compression posts, splay wires, perimeter clearance, and the clips the mill lists for that category
- Tile type, edge (square, tegular), and hold-down where the spec wants it
- Cuts at sprinkler drops, speakers, and linear diffusers — and whose fixture it is to furnish
- Height changes: each soffit is a new hang, not a leftover main tee
On gypsum ceilings, ACT estimators forget:
- Hang labor, screw class, and ceiling fastener spacing (tighter than walls)
- Tape, beads, and the finish level — bulkheads that die into ACT still get a finished gypsum return
- Control joints and perimeter relief; hard-screwing the lid to every partition kills the 50-foot / 2,500 number
- Listed fire-design layer count, Type C vs Type X, and insulation in the cavity
- Access panels
- Drywall-suspension tees, not ACT tees, when the lid is gypsum on grid
On both, the drywall-to-ACT joint is a detail: shadow mold, reveal, or a taped return. It is not “the grid will hide it.”
Commercial vs residential
Commercial wall and ceiling. Many W&C shops sell ACT and gypsum as one package to the general contractor. Keep the estimate split even if the contract is lump sum: different unions or crews in some markets, different material houses, different punch. The GC who “just needs a ceiling” still has a fire rating, a seismic category, and a finish schedule.
Residential production. Typical house work is gypsum to trusses or joists, often textured. ACT in a basement rec room is a different SKU and a different crew skill. Do not send a production hang crew to layout 2×2 grid with a chalk line and hope.
Tools follow the ceiling: rotary laser and wire on ACT and drywall-suspension; panel lift and screw gun on gypsum. See production tools and Tools.
Related directory
ACT systems: Acoustical ceilings (ACT), USG, Manufacturers. Gypsum finish and trims: Finishing. Steel that is not ceiling grid: Steel stud / framing.
FAQ
Can I hang gypsum on ACT grid?
Not on a lay-in tile grid. Drywall-suspension members are a different product, screwable, listed for board. Using ACT main tees as drywall furring is how you fail a hang and a listing.
Does a gypsum lid need seismic splay wires like ACT?
Not as a copy-paste of the ACT spec. Screw-attached gypsum on a suspension system has its own mill and code notes (diaphragm vs lay-in). Read the drywall-suspension catalog and the structural seismic category. Do not skip restraint because “it’s hard lid.”
Who owns the bulkheads?
Usually the drywall sub — gypsum wrap, hang, and finish — even when the field of the room is ACT. If the ACT contractor is a different shop, write the joint and the returns in the proposal.
Is drywall-suspension faster than direct-applied gypsum?
It can be, on a plenum full of duct. It is still a gypsum ceiling: board, tape, level, control joints. Price those.
Do residential control-joint rules apply to ACT?
No. ACT movement is grid and seismic language. Gypsum control joints are GA-216. A shop that owns both still uses both documents.