Which Frame Type Belongs on Your Opening?
This article helps contractors, facility managers, and project specifiers decide between drywall slip-on (knock-down) frames and continuously welded hollow metal frames. The choice affects installation sequence, structural performance, fire-rating compliance, and long-term serviceability -- and it has to be made before the wall goes up.
What Is a Drywall Slip-On Frame?
A drywall slip-on frame -- also called a knock-down (KD) drywall frame or C-profile frame -- is a three-piece hollow metal frame (two jambs and a head) shipped unassembled and installed after the partition wall is built. The frame literally slips over the finished drywall partition from both sides, with the jamb depth sized to wrap the total wall thickness. A compression anchor system clamps the frame tight against the gypsum board faces, eliminating the need for grouting or masonry embeds.
This is the most common frame type in light commercial construction, tenant improvement work, schools, and healthcare renovation -- anywhere you have steel stud and drywall partitions and need to sequence frame installation after rough framing is complete.
What Is a Welded (Continuously Welded) Frame?
A continuously welded (CW) frame is factory-assembled and shipped as a single rigid unit. All corners are welded, ground smooth, and finished from the factory. Welded frames are typically set before the wall is built around them -- the wall is constructed to the frame, not the other way around.
Welded frames are the standard for masonry construction (concrete block, brick, plaster) and for high-frequency or high-abuse openings where a rigid, monolithic frame is required. They are also the default for most fire-rated and labeled frame assemblies in demanding applications.
Side-by-Side: Key Differences
- Installation sequence: KD slip-on frames install after the wall. Welded frames install before or during wall construction.
- Wall type: Slip-on frames are designed for steel stud and drywall partitions. Welded frames are suited to masonry, plaster, and existing-wall retrofit situations as well as drywall (the CM Drywall Masonry profile uses a welded frame set prior to wall construction).
- Anchoring method: Slip-on KD frames use a compression anchor system that clamps against the drywall faces. Welded frames use masonry T-anchors, wire truss anchors, or weld-in anchors embedded in the wall as it is built up.
- Structural rigidity: Welded frames are inherently stiffer. KD frames rely on proper anchor installation and wall construction to achieve equivalent performance.
- Shipping and handling: KD frames ship flat and are easier to transport to upper floors or tight job sites. Welded frames are bulkier and require more care during handling.
- Field adjustability: KD frames allow minor field adjustment during installation. Welded frames are dimensionally fixed at the factory.
Fire-Rated Openings: What the Frame Type Requires
Frame selection on a labeled opening is not just a preference -- it is a compliance decision. Fire-rated assemblies must pair the correct frame label with the correct door label. A few key points installers and specifiers need to know:
- On labeled (fire-rated) frames in drywall, both a compression anchor system and a base anchor (foot clip) are required. The foot clip is mandatory for fire-rated frames regardless of wall type.
- Welded frames for fire-rated openings in masonry typically use weld-in masonry anchors set as the wall is constructed -- a process that must be coordinated with the masonry trades.
- The frame label governs the assembly. A lower-rated frame limits the assembly rating even if the door slab carries a higher listing. Verify the frame listing before the schedule ships.
- Fire door inspectors check frame labels, anchor conditions, and base anchors as part of annual inspection. Missing foot clips and improperly installed compression anchors are common field deficiencies.
Application Guide: Which Frame Belongs Where?
Use a Drywall Slip-On (KD) Frame When:
- The wall is steel stud and gypsum board and is already constructed or will be finished before the frame arrives
- The project is a tenant improvement, renovation, or phased build-out where sequencing is constrained
- The opening is light commercial, office, retail, or low-to-medium frequency traffic
- Budget or lead time favors stocked KD product (KD frames are widely available from distributor inventory)
- Upper-floor or elevator-only access makes shipping a rigid welded unit impractical
Use a Welded Frame When:
- The wall is masonry -- concrete block, brick, or poured concrete
- The opening is high frequency or high abuse: main corridors, school entryways, hospital cross-corridor pairs, industrial facilities
- The spec calls for a continuously welded frame or the AHJ requires it for the fire-rating assembly
- The opening requires a hospital stop (terminated stop at the floor), acoustical rating, or other specialty profile that is only available in welded construction
- The CM (Drywall Masonry) profile is specified -- this is a drywall-profile frame that ships welded and is set prior to wall construction, combining drywall frame geometry with masonry-style installation methodology
The CM Frame: A Hybrid Worth Understanding
The CM (Drywall Masonry) profile is a third option that confuses a lot of buyers. It uses the same drywall jamb-depth geometry as a standard C-profile KD frame, but it ships as a welded unit and is installed before the wall is built -- just like a masonry frame. Wall anchors are required; the compression anchor system is not used. If your spec calls for a welded frame in a drywall partition -- common in healthcare and education projects with strict fire-rating requirements -- the CM profile is likely what the engineer of record intends.
Expandable Drywall Frames: A Versatile Stock Option
For projects where wall thickness is not fully confirmed at time of order, expandable drywall frames offer more than three inches of adjustment to accommodate a range of finished wall thicknesses. Available in KD configuration, expandable frames can also be converted for use as masonry or welded frames. They are a practical solution for renovation projects where existing wall conditions are uncertain or variable across multiple openings.
Ordering the Right Frame: What Information You Need First
Before calling in a frame order or submitting a schedule, have the following confirmed:
- Wall type: Steel stud and drywall, masonry, or wood stud?
- Total wall thickness: Measured face-to-face of finished gypsum board, not just stud depth
- Opening size and door thickness: Frame jamb depth and rabbet are sized to the door
- Fire rating required: Label type, pressure rating (neutral or positive), and smoke label if required
- Hardware to be installed: Closer reinforcement, exit device prep, electrified hardware, and coordinator requirements affect both the frame prep codes and gauge selection
- Traffic frequency: Low, medium, or high determines whether KD or welded construction is appropriate per SDI guidelines
Frame Gauge and SDI Level
Frame gauge is matched to door level. The SDI pairing table is a useful starting point:
- SDI Level 1 door (20 or 18 ga): 18 or 16 ga frame
- SDI Level 2 door (18 ga): 16 ga frame
- SDI Level 3 door (16 ga): 16 or 14 ga frame
- SDI Level 4 door (14 ga): 14 or 12 ga frame
As a general rule: welded frames for medium and high frequency openings; KD frames for low frequency traffic areas. High-abuse environments -- school main entries, hospital corridor cross-pairs, industrial access points -- almost always warrant welded construction at Level 3 or Level 4 regardless of wall type.
Get the Frame Decision Right the First Time
Choosing the wrong frame type is an expensive mistake. A KD frame ordered for a masonry wall, or a welded frame that arrives after the drywall is already up, creates schedule delays and costly rework. The frame type decision belongs in the planning phase -- before the schedule ships and before the wall goes up.
DoorwaysPlus.com carries hollow metal frames in KD drywall, welded masonry, and specialty profiles for commercial, healthcare, education, and industrial applications. If you are working through a complex schedule or need to match an existing frame profile, our team can help you identify the right product and get it on the job.