Frames and code
Hollow metal door frames: profiles, anchors and frame depth
By the Div08 Consulting team · Updated
Hollow metal door frames are formed steel frames that hold the door, the hinges and the strike. Specifying one means choosing a profile (single rabbet, double rabbet or cased opening), a construction (welded or knock down), a gauge, a depth that matches the finished wall, and anchors that suit the wall type: masonry, steel stud, wood stud or existing.
Frame profiles
The profile is the cross section of the frame. The common ones:
- Double rabbet: a stop in the middle with a rabbet on each side. The most common commercial profile. One rabbet holds the door; the other can hold a door on the opposite side or just be trim. Equal rabbet and unequal rabbet versions exist.
- Single rabbet: one rabbet and one flat side. Used in thin walls or where the opening only needs one door and one stop.
- Cased opening: no stop at all. For openings with no door.
Every profile is described by its face dimension (the visible width of the frame face), the stop height, the rabbet width (which must suit the door thickness, usually 1-3/4 in. commercial) and the overall depth. Frame elevations on the drawings show the profile and the head and jamb widths.
Welded vs knock down frames
| Welded | Knock down (KD) | |
|---|---|---|
| How it ships | Corners welded at the factory, one piece | Head and jambs ship separately and assemble on site |
| When it is set | Usually before the wall is built (set and built in) | Often after the drywall is up (slip-on drywall frames) |
| Strength | More rigid; preferred for heavy traffic, large openings and security | Adequate for many interior offices and tenant work |
| Shipping and handling | Bulky, more damage risk | Compact, easier to stock and move |
| Fire rating | Widely available labeled | Many labeled KD frames are available; check the listing |
Spec tip
welded frames in drywall need to be set and braced before the studs are finished, which affects the GC's schedule. If the job is going to set frames after drywall, the spec should call KD slip-on frames, or the frames will arrive and wait.
Frame depth and gauge
Frame depth has to match the finished wall: the stud or masonry thickness plus the finishes on both sides. A wraparound drywall frame wraps the wall with its backbends; a butted frame sits between the wall surfaces. Ordering a frame for a nominal wall and then adding an extra layer of board on one side is a classic reorder. Schedule frame depths by wall type, and confirm wall types against the partition schedule during the submittal review.
Gauge is the steel thickness. 16 gauge is typical for interior commercial frames; 14 gauge is common for exterior, heavy traffic and larger openings; 12 gauge is used for high security or very heavy doors. Industry recommendations for standard steel doors and frames are in ANSI/SDI A250.8, and custom hollow metal is commonly specified to HMMA guidelines.
Hollow metal frame anchors
Anchors connect the frame to the wall. The anchor has to suit the wall construction, and a rated frame needs the anchors the label requires.
| Wall type | Typical jamb anchor | Notes |
|---|---|---|
| Masonry (built in) | Wire or strap (T) masonry anchors | Frame set first; anchors laid into the joints and the frame usually grouted |
| Steel stud | Steel stud anchors | Fastened to the studs at each jamb |
| Wood stud | Wood stud anchors | Fastened to the wood studs |
| Existing wall | Existing wall anchors (expansion or bolt type) | Fastened through the jamb, with spacers to avoid crushing the frame |
| Drywall slip-on (KD) | Compression anchors | Compression anchors bear on the studs; base anchors fasten the jambs at the floor |
Most frames also get base anchors at the floor (fixed or adjustable) to hold the jambs in place. The number of jamb anchors increases with frame height.
Hardware preparations
The frame is prepared at the factory for the hardware: hinge reinforcements and cutouts, the strike prep, closer reinforcement at the head, silencer holes in the stop and any electrified preps such as a door position switch or electric strike. Those preps depend on the door handing and the hardware sets, which is why the hardware schedule has to be approved before frames are released for fabrication.
Frequently asked questions
What is the difference between a single rabbet and double rabbet frame?
A double rabbet frame has a stop in the middle with a rabbet on each side; a single rabbet frame has one rabbet and a flat face. Double rabbet is the standard commercial profile.
Are knock down frames as good as welded frames?
For many interior openings, yes. Welded frames are more rigid and are preferred for heavy traffic, large or exterior openings and security doors.
How do you measure door frame depth?
Measure the finished wall thickness: the studs or masonry plus every layer of finish on both sides. The frame depth must match that dimension for a wraparound frame.
What gauge are hollow metal door frames?
Typically 16 gauge for interior frames and 14 gauge for exterior or heavy duty frames, with 12 gauge for high security.
General guidance only. Code requirements depend on the edition your jurisdiction has adopted and on the listing of each fire-rated assembly; confirm with the authority having jurisdiction. Published by Div08 Consulting (John Voll, owner).