Why the Frame Type Decision Happens Earlier Than Most People Think
This article is for commercial contractors, facility managers, and project architects who need to specify or order a hollow metal door frame and want to understand the practical difference between a drywall slip-on (KD) frame and a continuously welded frame. Getting this wrong is not just a product substitution problem -- it can mean a frame that will not fit the wall, an anchor system that does not match the installation sequence, or a fire-rated opening that fails inspection.
What Is a Drywall Slip-On Frame?
A drywall slip-on frame -- also called a KD (knocked-down) frame or a wrap-around frame -- is a three-piece hollow metal frame (two jambs and a head) that is assembled in the field after the drywall partition is already built. The frame literally slips over the finished wall opening from both sides, clamping around the partition thickness with a compression anchor system. No welding is required on site.
The profile code most commonly used for this type is the C-series drywall frame. On standard projects, the C-frame is shipped knocked down, prime painted, and assembled by the installer at the opening after walls are up. The jamb depth is specified to match the total partition thickness -- so knowing your exact wall build-up before ordering is not optional.
What Is a Welded Hollow Metal Frame?
A continuously welded (CCW) frame arrives at the job site as a single rigid unit -- the corners are welded and ground smooth at the factory. There is no field assembly at the frame corners. Welded frames are typically used in:
- Masonry walls, where the frame is set before the block or brick is laid
- Medium- and high-frequency traffic openings (schools, healthcare corridors, industrial facilities)
- Fire-rated openings requiring a labeled, continuously welded frame
- Openings where the frame must be placed prior to wall construction
The CM-series (Drywall Masonry) frame is a welded drywall-profile frame that installs before the partition is built -- it uses wall anchors rather than a compression anchor system. This is a common point of confusion: the CM frame looks like a drywall frame but installs like a masonry frame. Thermal break frames are not available in this configuration.
The Core Differences at a Glance
- Installation sequence: KD slip-on frames go in after the wall is built; welded and CM frames go in before or during wall construction.
- Field assembly: KD frames are assembled on-site at the corners; welded frames arrive as a finished unit.
- Anchor system: C-series KD frames use a compression anchor that clamps to the partition; masonry and CM welded frames use T-anchors, wire anchors, or wall anchors embedded into the structure.
- Gauge and duty level: Both frame types are available in 18, 16, and 14 gauge. Heavier traffic -- hospitals, school main corridors, industrial entries -- calls for 16 or 14 gauge regardless of frame type.
- Fire rating: Labeled (fire-rated) frames in drywall require both a compression anchor system AND a base anchor (foot clip) for KD frames. Welded frames for fire-rated masonry openings must meet ANSI A155.1 / UL-63 requirements. The frame label and the door label must be matched correctly -- the lower-rated component governs the assembly.
Which Frame Belongs on Your Project?
Use a Drywall KD (Slip-On) Frame When:
- The partition is already built or will be complete before frame installation
- The opening is in a light-gauge steel stud wall with drywall applied
- Traffic frequency is low to moderate (office interiors, retail stockrooms, lower-use school corridors)
- Budget and lead time favor a standard stocked KD frame
- The wall thickness is known and stable -- the jamb depth must wrap the full partition
Use a Welded Frame When:
- The opening is in masonry -- concrete block, brick, or CMU construction
- The frame must be set before the wall is built (masonry or CM profile)
- High traffic, abuse, or institutional use demands maximum rigidity (hospitals, school main entries, manufacturing)
- The spec calls for a continuously welded labeled frame for a fire-rated corridor or stairwell
- Aesthetics require fully flush, ground corners with no visible field assembly seams
A Note on Wall Thickness and Jamb Depth
The most common field mistake with drywall slip-on frames is ordering the wrong jamb depth. The frame must wrap the entire partition -- studs, drywall on both faces, and any furring or finish material. A 3-5/8" stud wall with 5/8" drywall on each side produces a total partition thickness of approximately 4-7/8". Ordering a 4-3/4" jamb depth frame for that wall means the frame will not close properly and the compression anchors will not engage. Always confirm the finished wall build-up -- not the stud size alone -- before specifying jamb depth.
Expandable drywall frames are available for situations where the exact partition thickness is uncertain or variable. These frames ship knocked down and adjust across a range of jamb depths, reducing the risk of a mis-sized order on a job with inconsistent wall conditions.
Fire-Rated Openings: What Changes
On labeled openings, frame type selection is not just a field convenience decision -- it is a code compliance issue. Key points:
- The frame listing must be compatible with the door slab listing. A frame rated for neutral pressure paired with a positive-pressure door produces a neutral-pressure-only assembly.
- KD drywall frames on fire-rated openings require both the compression anchor system and a foot clip (base anchor) at each jamb. Neither can be omitted.
- Hospital stop (terminated stop) cutouts on fire-rated frames are limited to a maximum 6-inch filler height and must be factory-installed or completed by an authorized fabrication shop.
- Continuously welded frames offer a cleaner compliance path on high-scrutiny fire-rated openings because the corner construction is not dependent on field assembly quality.
Practical Takeaway for the Job Site
If your sequence of construction is set before the frame order goes in, the decision largely makes itself: wall already up means KD slip-on; wall not yet built in masonry means welded. The harder call is a drywall opening with a high-frequency or fire-rated requirement -- that is where gauge selection, anchor specification, and labeled frame coordination matter most.
DoorwaysPlus.com carries hollow metal frames across the full range of profiles, gauges, and configurations for masonry, drywall, and specialty applications. Whether you are pricing a single opening retrofit or a full building schedule, our team can help you match the right frame to the wall type, fire rating, and hardware prep before the order ships.
Questions about frame profile, jamb depth, or labeled opening coordination? Contact the team at DoorwaysPlus.com -- we work through frame schedules every day.