Field note
H-stud area-separation walls for townhouses
A townhouse party wall that is a gypsum area-separation wall is not a cavity shaft, not a 3-5/8 drywall partition, and not two 2×4 walls with Type X. It is a 2-inch H-stud chassis, two thicknesses of 1-inch Type X liner, C-runners, and aluminum breakaway clips to the flanking wood (or steel). Gypsum Association GA-620 is the association document for that class. Manufacturer ASW folders are the kit you actually buy.
This page is for the shop that sees the wall on a multifamily or townhouse bid — residential production with a commercial-looking assembly, or a W&C shop on wood framing. Sequence that is shared with liner systems is on shaftwall installation. What follows is the townhouse / multifamily wall as a bid and detailing problem, and why it is distinct from shaftwall.
What the assembly is (and is not)
Is: a listed gypsum firewall meant to stay standing if the unit on the fire side collapses. The aluminum clip is the fuse: heat lets that structure fall away without dragging the liner wall down. Two liner panels, vertical, edges captured in H-studs at 24 inches o.c. (liner width). Floor and head C-runners. Stacked lifts with back-to-back runners where the wall continues up through the next floor. An air gap between the ASW and the adjacent framing — manufacturer public notes in this class commonly show a 3/4-inch gap; build the gap the catalog on the submittal draws.
Is not cavity shaftwall. Shaftwall uses J-runners and C-H / C-T / I-studs, one liner in the cavity, and occupant-side face layers. Elevators and stairs. One-sided erection into a hole. Different members, different listing, different takeoff line. Do not send H-studs to a shaft, and do not send shaft studs to a townhouse party wall.
Is not a conventional metal-stud demising wall with 5/8 Type X both sides. That wall can be a fire partition. A fire wall between townhouse units is a different IBC / IRC problem — continuity, structural independence, and a rating the drawings name (commonly a 2-hour class in gypsum ASW catalogs; sprinklers and code edition may allow another). Match the listed design. It is not an STC partition.
Liner is shaftliner — 1-inch, usually 24 inches wide, double-beveled. Paper-faced or glass-mat. PABCO, National Gypsum, USG, and peers sell the panel; ClarkDietrich and MarinoWARE sell the H-stud and clip package that matches. Directory steel: Steel stud / framing.
Townhouse conditions the shaftwall folder does not cover
Flanking is wood. Production townhouses are wood floor, wood roof, sometimes light-gauge interior. Clips go to that framing after it is up: short leg to H-stud with pan-head Type S; long leg to wood with Type W (Type S if the flanking is steel). Clip schedule and height limits are in the listed design. They change with wall height and with one-sided vs two-sided attachment. Do not copy a spacing from another mill.
The wall stacks. Each story is a lift. C-runner caps the liner; the next floor’s runner sits back-to-back or as the catalog details. Stagger runner end joints. The ASW is continuous through occupied floors; how it dies at the roof, attic, and foundation is a system detail, not a drywall-partition head. Parapet, attic separation, and roof intersection are where shops donate rework when the drawing is a single wall type with no section.
Plumbing and boxes do not live in the H-stud. The liner wall is a fire wall. Penetrations are listed firestop problems, not a residential boring pattern. Keep DWV and electrical in the flanking cavities. A back-to-back box through both liners is how you fail the listing.
Finish gypsum is on the unit framing. The room-side board hangs on the townhouse’s wood (or steel) studs, across the air gap — not as a conventional face layer on the H-stud unless the listed design says otherwise. That is a different hang than production Type X on a stud. Do not screw the finish board to the H-stud “to stiffen it” and close the gap.
Weather. The ASW often stands before the roof and the flanking walls. Paper liner that takes rain is a callback the gypsum house will not eat. Glass-mat liner is the product class sold for longer exposure. Cover the top of the lift. Do not leave C-runners full of ice and call it a winter condition.
Breakaway clips are not optional. Skipping the second side because the wall “felt solid,” substituting steel clips, or using a drywall angle as a clip, defeats the reason the wall is an ASW. The adjacent structure is supposed to be able to fail.
Who owns the number
On wood multifamily, area separation may sit in the drywall / wall-and-ceiling number, in a residential production package, or as a specialty line the GC pulled out. Read the bid scope.
Price, at minimum:
- Matched H-studs, C-runners, and liner (not leftover 5/8 ripped to 24 inches)
- Aluminum breakaway clips, both sides, at the listed schedule
- Stacked-floor runner labor and any catalog splice
- Glass-mat liner or weather protection if the wall stands open
- Penetrations and firestop only if they are in your number — write the exclusion if they are not
- Finish board on the unit framing as a separate hang line
- Access, lifts, and one-sided work in a narrow unit bay
Limiting height and clip layout are tables. Do not bid a three-story townhouse stack on an office-partition height habit. Interior C645 drywall stud tables do not size an H-stud fire wall.
What not to do
- Mix shaftwall C-H / J members into an H-stud ASW, or the reverse
- Use steel clips, framing angles, or skipped clips
- Hang unit-side board on the H-stud and erase the air gap
- Run plumbing in the liner cavity
- Leave paper liner in the weather through a winter
- Treat the head at the roof like a slotted drywall track
- Call a double 2×4 + Type X wall an ASW because both are “two-hour class” in conversation
Commercial vs residential
Residential production / multifamily wood. This is where the assembly actually shows up: townhouses, stacked flats, some hotels on wood. The hang crew that only stocks 1/2-inch regular needs a different trailer: liner, H-stud, clips, glass-mat if exposed.
Commercial W&C. Cavity shaftwall is the everyday liner job (elevators, stairs). H-stud ASW appears when the same shop takes mixed-use or wood multifamily. Keep the two liner systems on two takeoff lines. Podium concrete with wood over it still wants the ASW detailed at the podium and at the wood — two conditions.
Related directory
Liner: USG, PABCO Gypsum, National Gypsum, Manufacturers. H-stud and clips: Steel stud / framing, ClarkDietrich, MarinoWARE. Sequence overlap: shaftwall installation.
FAQ
Is an H-stud area-separation wall the same as shaftwall?
No. Different studs, different runners, different listing, different job (party fire wall vs shaft). See shaftwall installation.
Can I rip 5/8 Type X and stand it in H-studs?
No. Wrong thickness, wrong edge, wrong listing. Liner is 1-inch shaftliner.
Do the aluminum clips go on before the wood walls?
Clips tie the ASW to flanking framing. Set the liner wall, frame the units, then clip per the mill. Do not skip a side.
Is the 3/4-inch gap required?
Build the gap the listed design and the manufacturer detail show. Public ASW notes in this class commonly draw a 3/4-inch air space. Do not close it with finish board.
Who owns firestop at plumbing that someone ran through the ASW?
Qualify it. The liner package and the firestop package both touch it. The penetration still has to be a listed detail, not foam from the truck.