Field note
Head-of-wall joints and firestop coordination for the drywall sub
The head of a rated partition is not leftover track foam. It is a tested joint between a fire-resistance-rated wall and the floor or roof construction above it. The drywall sub builds the wall that creates the gap. The firestop trade often fills it. Inspections fail when those two numbers do not meet in the same place.
This page is bid and field coordination for the commercial wall-and-ceiling sub. It restates public class language from UL 2079 / ASTM E1966 (fire-resistive joint systems), the IBC fire-resistant joint systems chapter, ASTM C754 / AISI S220 for interior nonstructural stud, GA-216 / ASTM C840 for the gypsum face, and manufacturer deflection-track notes (ClarkDietrich and peers). It is not a reprint of a UL HW-D sheet and not a license to caulk the deck with acoustical sealant. A house top plate under trusses is not this joint.
What the joint actually is
A head-of-wall (HOW) is the linear joint at the top of a fire-resistance-rated partition where it meets floor or roof construction. UL classifies these as joint systems — commonly HW-D (dynamic, cyclic movement) or HW-S (static). Dynamic is the everyday commercial condition: the deck will live-load.
Through-penetrations (ASTM E814 / UL 1479) are a different family. A pipe sleeve in the wall is not this page. Neither is a control joint in the gypsum face. Deflection track is not a GA-216 control joint, and a vinyl reveal is not a head-of-wall.
The listing — UL Product iQ or the firestop manufacturer’s current PDF — names hourly rating, movement class, floor/roof type, the UL / GA-600 wall construction, joint width, fill (mineral wool, sealant, spray, gasket, intumescent, or manufactured track), and which sides get treated. Do not assume leftover 1-hour caulk covers a 2-hour deck joint. The joint listing is its own document.
Who owns the gap
This is the bid fight. Write it in the proposal. Typical split the trailer actually sees:
Drywall / wall-and-ceiling number (Division 09) usually owns:
- Interior steel stud and track, including slotted or deep-leg deflection track when that is how the wall is detailed
- Studs cut short of the deck so the wall can move — the mill’s gap, not a guess
- Gypsum held down from the underside of the deck or flute, per the joint listing and GA-216 / C840
- Cavity insulation when it is in the drywall package
- Sometimes the mineral wool packed into the head joint, because the hang crew is there before the firestop truck
Firestop number (Division 07 firestopping) usually owns:
- The listed joint system: elastomeric sealant, fire spray, intumescent, and the mineral wool in the joint when the spec put safing with firestop
- Submittal of the HW-D / HW-S sheet
- Special-inspection coordination where the AHJ requires it
Neither number owns it when both estimators excluded it. That is how a GC gets a change order at the deck.
Qualify, in writing: deflection track in the metal-stud package; mineral wool at the head; listed sealant/spray; flute fill (wall perpendicular vs parallel to flutes); shaftwall heads as the shaft system’s listed head, not a generic partition HOW. Acoustical sealant at an STC perimeter is not the fire-resistive joint. You can owe both.
Deflection is a framing detail before it is firestop
Interior nonstructural studs (ASTM C645, AISI S220, installation ASTM C754) are not supposed to carry the floor. The head is detailed so live load can happen without crushing the partition or tearing the finish.
Common head conditions — confirm the mill and the drawing:
- Solid track where the documents say the deck is not moving. Still not a license to jam gypsum to the steel.
- Slotted deflection track — studs clipped or otherwise held in the slots; they are not welded to the head.
- Deep-leg / double-track — nested tracks that allow the same movement class.
- Fire-rated / intumescent deflection track — a manufactured member with a listed strip or gasket, sold so part of the joint fill lives in the steel package (ClarkDietrich, MarinoWARE, and peers). Still a listed system. Still not leftover foam.
Stud length: cut to the published gap under that track. Steel stud framing basics flags the same rule. Do not stand a full-height stud, crush it into the deck, and then ask firestop to “make it rated.”
Gypsum at the head is typically held short of the deck so the joint has a designed width. Fastening the face layer to a slotted track in a way the listing forbids is how you lock the wall. Read the track catalog and the HW sheet together. Type S into light-gauge head members — Type S vs Type W. Limiting height and deflection ratio (L/240 vs L/360 and whatever the structural notes say) are a stud-table problem, not a thicker bead of sealant.
Mineral wool is not a generic stuffing
Head-of-wall listings that use safing name mineral wool (stone wool / slag wool) of a density and compression the system was tested with. Fiberglass batt leftover from the partition cavity is not a silent substitute. Neither is a wad of scrap gypsum.
Pack the joint the way the listing draws it — full width, compressed as that sheet requires. Do not leave a path at the stud web. Fluted decks add a flute-fill condition when the wall runs perpendicular to the flutes; parallel-to-flute is a different detail.
Cavity insulation in the stud bay is a different line. See insulation in the drywall number and Insulation — Johns Manville, Owens Corning, and peers. SAFB in the wall does not equal safing at the head.
Field sequence
Frame with the specified head track and confirm the gap. Hang the first face; leave the designed joint width at the deck. Install cavity insulation if it is in this package. Hang the second face — same joint width; do not close the head with a full-height sheet “to look tight.” Firestop (whoever owns it) installs the listed fill before finish hides the joint, or as the listing allows relative to taping. Tape and finish gypsum to the GA-214 level below the joint. The firestop bead is not a Level 4 skim.
Do not paint over a fire-spray the listing wants left exposed, and do not leave raw wool in a corridor because the firestop truck is late. Shaftwall heads follow the shaft catalog (J-runner, liner cut short, listed shaft HOW) — not slotted drywall track.
Commercial vs residential
Commercial wall and ceiling. Rated corridors, demising walls, and shaft-adjacent partitions under steel deck or concrete. The joint is in the W&C coordination set even when Division 07 holds the sealant.
Residential production. Typical wood-frame houses do not bid UL 2079 head-of-wall. Multi-family wood, garage separations, and mixed-use podiums do. Top-plate fire caulk from a house habit is not a listed dynamic joint under metal deck.
Bid notes
Price or exclude, in writing:
- Deflection track (slotted, deep-leg, or listed intumescent), not generic runner
- Extra gypsum waste from holding board down at every rated head
- Mineral wool at the joint or a clear exclusion
- Flute fill
- Fire-resistive joint sealant/spray or a clear exclusion to Division 07
- Shaft and area-separation heads as their own listed systems
- Access for the firestop trade (second-side work after one face is up)
Related: Steel stud / framing, Insulation, Manufacturers, Products, Guides.
FAQ
Can I fill the head with acoustical caulk and call it firestop?
No. STC perimeter seal is not a UL 2079 joint. Use the listed system.
Does deflection track replace the firestop joint?
Only when that exact track is part of a listed head-of-wall system and is installed as that system. Generic slotted track plus hope is not a listing.
Who cuts the board short — drywall or firestop?
Drywall. The hang creates the joint width. Firestop fills what you left.
Is mineral wool in the drywall number?
Only if the scope says so. Many specs put safing with firestop. Many GCs still expect the drywall sub to pack it. Qualify.
Do residential garage walls need HW-D joints?
A wood-frame garage separation follows its listed wall design and local code — not a metal-deck HW-D copied onto a wood top plate.