Shaftwall and area-separation sequence for the drywall sub

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Cavity shaftwall and area-separation walls are why a commercial drywall sub owns 1-inch liner, J-runners, and a stud that is not a 3-5/8 drywall C. Both systems are erected from the accessible side. Both fail inspections when someone hangs leftover 5/8 Type X and calls it liner.

This page is a field and takeoff sequence. It paraphrases public manufacturer class language (USG cavity shaft wall, ClarkDietrich shaftwall and area-separation systems, National Gypsum / PABCO liner notes) and Gypsum Association GA-620 for gypsum area-separation firewalls. It is not a reprint of a system catalog and not a substitute for the listed UL / GA-600 design on the drawings. Pull the current PDF from the mill that is on the submittal.

Two systems, same liner family

Cavity shaftwall (elevators, stairs, mechanical shafts): J-runners at floor, head, and ends; 1-inch shaftliner standing vertically in the tabs; C-H, C-T, or I-studs (the catalog name for that mill); occupant-side face layers to the listed design. Non-load-bearing. The selling point is one-sided erection when the shaft is already a hole.

Area-separation walls (multi-family party / townhouse firewalls): typically two thicknesses of 1-inch Type X liner in 2-inch H-studs, C-runners at floor and head, aluminum breakaway clips to the flanking wood (or steel) framing. GA-620 is the association document for that assembly class. The wall is meant to stay standing if the unit on fire collapses.

Do not mix the members. An H-stud area-separation wall is not a cavity shaft. A C-H shaft stud is not a 6-inch drywall stud with thicker board. Liner is shaftliner — 1-inch, usually 24 inches wide, double-beveled — paper-faced or glass-mat. Glass-mat liner (PABCO GLASS and peers) is sold for longer weather exposure on an open shaft. Paper liner is not a rainscreen.

Steel for both packages: ClarkDietrich, MarinoWARE, and the gypsum houses that sell a matched system. See steel stud framing basics.

Cavity shaftwall — sequence the crew actually runs

Manufacturer folders (USG SA-class shaft wall, ClarkDietrich shaftwall, National Gypsum cavity shaftwall) describe the same order of operations. Confirm the catalog you bought.

  1. Layout. Snap the partition. Confirm depth (2-1/2, 4, 6 inch are the everyday cavities) against the listed design and the limiting-height table for the design lateral load. Elevator and stair shafts see stack-effect and piston pressure the office partition does not. Use the mill’s height table, not a 25-ga drywall habit.
  1. J-runners. Floor, head, and vertical ends. Unequal legs: the long leg faces the shaft (backstop for the liner); the short leg faces the finish side. Fasten to structure at both ends and at the spacing the catalog names (commonly not more than 24 inches o.c.). Powder-actuated or screw, matching the deck. If the structure will be spray-fireproofed, set the runners before spray and clean overspray off the steel before liner goes in — USG’s public liner tips say exactly that.
  1. Cut liner and studs short of height. System notes cut liner on the order of 3/4 inch to 1 inch less than floor-to-ceiling, and shaft studs a similar or slightly tighter gap (USG’s public C-H note is 3/8 to 1/2 inch less), so members sit in the J without crushing. Read the folder you are building. Do not jam a full-height liner into a deflection condition.
  1. First liner, plumb, against the vertical J. Some catalogs want Type S screws through the long leg into that first panel; some friction-fit and bend optional tabs. Follow the mill on the job.
  1. Stud, then liner, then stud. Shaft studs drop into floor and head J and rotate or slide so the tabs / C-H flanges capture the liner edge. Next 24-inch liner engages the open side. Repeat. Typical spacing is 24 inches o.c. because that is the liner width — the design may tighten it. Do not stretch a 24-inch liner across a 32-inch stud bay.
  1. Horizontal liner joints. When the wall is taller than stock, manufacturer notes put end joints in the upper or lower third of the height, stagger adjacent panels, and (on I-studs) require enough length to catch more than one tab. Shaftliner end joints in the cavity are not a Level 4 tape joint.
  1. Terminations and openings. Full-height E-studs or J-runners at T-intersections, corners, columns, and jambs. Heads and sills of openings get J. Door and damper openings are system details, not a wood-frame header habit. Smoke/fire dampers have to match a listed shaftwall condition — that is coordination, not a field invention.
  1. Face layers on the occupant side. The listed design names thickness, core (Type X or Type C), layer count, orientation, and fastener. A common 1-hour face is a single 5/8 Type X; a common 2-hour face is two layers (1/2 Type C or 5/8 Type X depending on the design). Fasteners are Type S into light-gauge shaft steel, Type S-12 into heavier members — see Type S vs Type W. Stagger joints. Finish the occupant face to the GA-214 level on the finish schedule. The liner face inside the shaft is not a paint-grade wall.

Caulk the perimeter when the shaft will see air pressure. Mineral wool or SAFB in the cavity only if the design calls for it — Insulation, Johns Manville and peers. Head-of-wall firestop is a tested joint, not leftover deflection-track foam. Control joints in long gypsum faces still follow GA-216; a J-runner is not a corridor control joint.

Horizontal shaftwall (stair soffits, corridor ceilings in some catalogs) is the same liner family on its side, with its own hanger and rating details. Do not hang it like a drywall-suspension ceiling.

Area separation — GA-620 class sequence

Gypsum area-separation firewalls are a different bid, often on multi-family wood framing that a residential production shop or a commercial W&C shop may both see. Public GA-620 language and manufacturer ASW folders agree on the kit:

  • Floor and end C-runners
  • Two layers of 1-inch Type X shaftliner, vertical, edges in 2-inch H-studs
  • C-runner cap at the head of each lift; stacked courses with back-to-back runners where the wall continues up
  • Aluminum breakaway clips from each H-stud (and vertical C-runner) to the flanking framing, both sides except at an exterior exposure detail the catalog draws

Sequence the crew runs:

  1. Set floor C-runner. Stand a vertical C-runner at the start.
  2. Set two liner panels into the runners. Slide an H-stud over the long edges until the liner hits the web.
  3. Next pair of liners, next H-stud, 24 inches o.c. Cap the lift. Fasten C-runner corners both sides with pan-head Type S as the mill shows.
  4. Stack the next floor: stagger runner end joints; fasten runner to runner per the catalog.
  5. After flanking framing is up, install aluminum clips. Short leg to the H-stud with pan-head Type S; long leg to wood with Type W (or Type S to steel framing). Clip schedule and height limits are in the listed design and the liner manufacturer’s notes — they change with wall height and with one-sided vs two-sided attachment. Do not invent a spacing from another mill’s folder.
  6. Leave the air gap the system calls for between the ASW and the adjacent framing (ClarkDietrich’s public ASW notes show a 3/4-inch gap class of detail). Finish gypsum on the unit side is hung on that unit’s framing, not treated as a conventional face layer on the H-stud unless the listed design says otherwise.

The clip is the fuse. Aluminum is specified so heat on the fire side lets that structure fall away without dragging the liner wall down. Steel clips are not a silent substitute. Do not skip clips on the second side because the wall “felt solid.”

Weather: glass-mat liner if the wall will sit open. Paper liner that takes rain is a callback the gypsum house will not eat.

What not to do

  • Rip 5/8 Type X into 24-inch strips and call it liner. Wrong thickness, wrong edge, wrong listing.
  • Swap a 20-ga drywall C for a C-H or H-stud because the trailer was short.
  • Hang occupant-side board before the liner and studs are in and plumb — you just closed the only side you can work from.
  • Carry a residential 16-inch Type W pattern onto shaft face layers.
  • Treat shaftwall head-of-wall like an unrated slotted drywall track.
  • Put a vinyl corridor control joint into a shaft cavity and assume GA-234 backup appeared by itself.

Bid notes for the drywall sub

Cavity shaftwall is almost always in the commercial wall-and-ceiling number. Area separation may sit in that number or in a multi-family wood package — read the bid scope. Price:

  • Liner, matched studs and J or H / C-runners (not generic drywall track)
  • Face-layer board and the extra fastener length on multi-layer faces
  • Openings, dampers, E-studs, breakaway clips
  • Perimeter sealant and any listed insulation
  • One-sided production (lifts, staging at the shaft) vs two-sided office partitions
  • Weather protection or glass-mat liner if the shaft or ASW stands open

Limiting height is a table, same rule as interior stud. ClarkDietrich and the gypsum system holders publish those tables. Do not bid a tall elevator shaft on an office-partition height rule.

Related directory

Liner and systems: USG, PABCO Gypsum, National Gypsum, Manufacturers. Shaft studs and J / H members: Steel stud / framing, ClarkDietrich, MarinoWARE. Screws: Fasteners. Cavity insulation: Insulation.

FAQ

Is shaftwall just 6-inch stud and Type X?

No. It is a liner-panel system with dedicated shaft studs and J-runners. Wrong members fail the listed design.

Can I erect cavity shaftwall from inside the shaft?

The system is designed for erection from the floor / occupant side. If the shaft is accessible both sides, you still build the listed members — you do not get to substitute a conventional partition because you can reach the back.

Does the liner get finished?

Not to a paint-grade Level 4 inside the shaft. Occupant-side face layers follow the finish schedule.

Are area-separation clips optional?

No. Aluminum breakaway clips are part of the GA-620 class assembly and the listed designs. They are how the fire-side structure is allowed to fail without pulling the wall down.

Can I use EQ drywall stud in a shaft?

Only if that exact member is in the listed shaftwall system. EQ interior drywall stud is not a generic substitute for C-H, C-T, I-stud, or H-stud.

Who owns head-of-wall firestop on a shaft?

Write it in the bid clarifications. The metal-stud / liner package and the firestop package both touch it. The joint still has to be a tested head-of-wall, not a bead of acoustical caulk.