Field note
Shaftliner types: paper, glass-mat, and what is not liner
Shaftliner is a 1-inch Type X liner panel, usually 24 inches wide, double-beveled on the long edges so it drops into J-runners, shaft studs, and H-studs. It is not 5/8 Type X ripped into 24-inch strips. Wrong thickness, wrong edge, wrong listing.
This page is the product conversation. Sequence lives on shaftwall installation and townhouse area separation. Class language is public: Gypsum Association shaftliner notes, ASTM C1396 (paper-faced shaftliner / coreboard), ASTM C1658 (glass-mat gypsum panels, including liner), and mill liner folders from USG, PABCO, National Gypsum, Georgia-Pacific, and peers. Pull the current PDF. Product door: Products.
What the panel is
Gypsum Association physical description for the class: 1 inch thick, 24 inches wide, lengths commonly 8 to 12 feet (some mills run longer). Noncombustible Type X core. Long edges beveled (double-bevel is the everyday liner) so the panel engages framing tabs. Ends square.
Two facers, two ASTM families:
Paper-faced liner — ASTM C1396 shaftliner / water-resistant shaftliner language. Heavy paper, often treated for moisture and mold. This is the closed-building liner: elevator and stair shafts after the envelope can protect paper, area-separation lifts that will not sit in weather. Paper liner is not a rainscreen. Rain in an open shaft or an open townhouse party wall is a callback the mill will not eat.
Glass-mat liner — ASTM C1658 (mills also cite C1396 Type X core language). Fiberglass mat face and back, often folded around the bevels. Sold for longer weather exposure on shafts and area-separation walls that stand before the building is closed in. Exposure time is the mill’s warranty window, not a license to leave any liner as cladding. PABCO GLASS shaftliner and USG glass-mat liner are this class — named products in the listings that call them.
Both are Type X liner, not Type C wallboard. Occupant-side face layers may be Type X or Type C per the design. Do not confuse the 1-inch core in the cavity with the 5/8 (or 1/2 Type C) on the finish side.
UL type designations on the edge (mill-specific letter codes) are what the fire design actually listed. “1-inch liner” on a takeoff that does not match the edge stamp is still the wrong panel.
Two systems, same liner family
Cavity shaftwall (elevators, stairs, mechanical shafts): one liner thickness in C-H / C-T / I-studs and J-runners, face layers on the occupant side. One-sided erection. See shaftwall installation.
Area-separation walls (townhouse / multi-family gypsum firewalls): two 1-inch liners in 2-inch H-studs, C-runners, aluminum breakaway clips. GA-620 class. Same liner SKU family, different members, different listing.
Do not send glass-mat interior wall panels (DensArmor-class, 5/8) as liner. Do not send exterior glass-mat sheathing as liner. Width, thickness, edge, and listing are all wrong.
What not to substitute
- Ripped 5/8 or 1/2 Type X — not 1 inch, not a liner edge, not in the shaft or ASW listing.
- Coreboard sold for solid gypsum partitions if the listing named shaftliner — related 1-inch family, different edge and system. Use the named liner.
- Regular 1-inch anything that is not Type X liner.
- Paper liner in an open shaft or ASW when the mill and the spec wanted glass-mat.
- A different mill’s liner in a proprietary UL type listing.
Mold-resistant paper liner is still paper. It is not glass-mat. ASTM D3273 scores on a data sheet are not a weather window.
Hang and finish are not Level 4 on the liner face
Liner stands vertical in the framing. Cut short of floor-to-head so it sits in the J or C without crushing — the catalog gap, not a guess. Horizontal liner splices in a tall shaft are system details (stagger, location in the height), not taped Level 4 joints inside the shaft.
The liner face toward the shaft is not a paint-grade wall. The occupant face layers are finished to the GA-214 schedule. Area-separation finish gypsum hangs on the unit framing, across the air gap, not as a conventional face on the H-stud unless the listing says so.
Steel is the matched shaft or H-stud package — steel stud framing, ClarkDietrich and peers — not a 3-5/8 drywall C.
Commercial vs residential
Commercial W&C. Cavity shaftwall is a core scope. Take off liner type (paper vs glass-mat), length vs shaft height, and the mill UL type the design named. Glass-mat liner is the prerock / open-shaft line.
Residential production / multi-family. Townhouse ASW is where a production shop meets 1-inch liner. Same product class as commercial shaftliner. Weather on an open party wall is why glass-mat liner is on that takeoff. A house garage 5/8 Type X wall is not liner.
Bid notes
- Own line: 1-inch liner, width 24 inches, facer paper or glass-mat, mill type as listed.
- Own line: shaft studs / H-studs / J or C-runners — not drywall track.
- Waste: cut-off at head, openings, stacked ASW lifts.
- Do not convert liner square feet from 5/8 Type X leftovers.
Related directory
Choosing drywall type, Products, Manufacturers. Sequence: Shaftwall installation, H-stud area-separation walls. Mills: USG, PABCO Gypsum, National Gypsum, Georgia-Pacific Gypsum.
FAQ
Can I rip 5/8 Type X for liner?
No.
Is glass-mat liner the same as DensGlass-class sheathing?
No. Sheathing is an exterior cladding substrate, usually 48 inches, different ASTM (C1177). Liner is 1-inch, 24-inch, shaft/ASW listed.
Does paper mold-resistant liner replace glass-mat for open shafts?
Not as a class. Open-shaft weather is the glass-mat liner’s job when the mill window applies.
Does the liner get taped to Level 4?
The shaft-side liner face generally does not. Occupant-side face layers do, to the finish schedule.
Is 1-inch liner Type C?
It is Type X liner. Face layers might be Type C. Read the design.