Commercial door frames fall into three primary construction types: knocked down (KD), welded, and drywall slip-on (also called wrap-around). Each frame type is designed for a specific wall construction and installation sequence. Knocked down frames ship as separate pieces and assemble on-site, making them the standard choice for drywall and metal stud walls. Welded frames arrive fully assembled with welded corners and are set into masonry or concrete block walls during construction. Drywall slip-on frames install after the wall is finished by wrapping around the completed drywall opening. The anchoring method used with each frame type depends on the wall construction, fire rating requirements, and structural loads.
CDF Distributors fabricates and ships hollow metal frame assemblies from its Nashville, Tennessee facility. You can configure frame assemblies online using CDF’s ProBuilder tool at cdfdistributors.com. For assistance selecting the correct frame type and anchoring method for your project, call (855) 769-9895 or email sales@cdfdoors.com.
Hollow Metal Frame Terminology
Every hollow metal door frame consists of the same fundamental components, regardless of whether the frame is knocked down, welded, or drywall slip-on. Understanding these terms is essential for specifying the correct frame and communicating with suppliers, architects, and installers. The following table defines the standard terminology used across the commercial door industry.
Frame Component Definitions
Head | The top horizontal piece of the door frame that spans the width of the opening. |
Strike Jamb | The vertical side of the frame on the lock side of the door. The strike plate mounts to this jamb. Double doors have two hinge jambs and no strike jamb. |
Hinge Jamb | The vertical side of the frame on the hinge side of the door. Hinges mount to this jamb. |
Face | The exposed, visible surface of the frame profile that faces outward from the wall. |
Throat | The opening between the backbends of the frame. The throat dimension must match the wall thickness. |
Jamb Depth | The overall width of the frame profile, measured as the face-to-face dimension. This measurement determines the wall thickness the frame can accommodate. |
Stop | The raised portion of the frame profile that the door closes against. The stop controls the door position when closed and provides a seal surface. |
Rabbet | The area on either side of the soffit where the door sits when closed. Frames are available in single rabbet (single door) or double rabbet (pair of doors) configurations. |
Soffit | The area on the frame between the rabbets. On a single rabbet frame, the soffit is the recessed area between the stop and the face. |
Backbend | The return at the back edge of the frame profile that wraps around the wall surface. The backbend anchors the frame to the wall and provides a finished edge. |
Base Anchor | The bottom attachment point of each jamb where the frame is secured to the floor or wall base. |
Labeled cross-section showing: face, throat, jamb depth, stop, rabbet, soffit, and backbend. This diagram requires CDF approval before inclusion in the production file.
Labeled front-view diagram showing: head, hinge jamb, strike jamb, and their relationship to the door opening. This diagram requires CDF approval before inclusion in the production file.
Commercial Door Frame Types
Commercial hollow metal frames are manufactured in three primary construction types. Each type is engineered for specific wall constructions, installation sequences, and project requirements. The following sections explain the construction, applications, and key characteristics of each frame type.
Knocked Down (KD) Frames
A knocked down frame ships as three separate pieces: the head and two jambs. The pieces interlock at the corners using tabs and slots, then are secured with screws or by bending the tabs during installation. KD frames are the most common frame type in commercial construction because they can be installed after the wall is built, which simplifies the construction sequence and reduces the risk of damage during the building process.
KD frames are available for both drywall and masonry wall constructions. In drywall applications, the frame wraps around the finished wall opening. In masonry applications, KD frames can be set after the block wall is built using expansion anchors or through-bolts. KD frames are available in fire-rated configurations up to 90 minutes for drywall walls and up to 3 hours (180 minutes) for masonry walls.
Construction | Three separate pieces (head and two jambs) that interlock on-site |
Wall Types | Drywall over metal studs, drywall over wood studs, masonry (CMU) |
Installation Timing | After wall construction is complete |
Corner Connection | Interlocking tabs and slots, secured by bending tabs or with screws |
Fire Rating Range | 20-minute, 45-minute, 60-minute, 90-minute (drywall); up to 3-hour/180-minute (masonry) |
Common Applications | Offices, healthcare facilities, schools, retail, hospitality |
Shipping | Flat-packed; reduces shipping damage and freight cost |
Welded Frames
A welded frame is a one-piece assembly with corners that are factory-welded, ground smooth, and finished before shipping. Because the corners are permanently joined, welded frames offer the highest structural rigidity and are the standard choice for masonry and concrete block walls. Welded frames are typically set in place before or during wall construction, with the masonry built up around the frame.
Welded frames are required for most high-security applications and for openings that require the highest fire ratings. Because the frame is one piece, it must be maneuvered into position as a complete unit, which can be more challenging in renovation projects where walls are already in place. Welded frames support fire ratings across the full range: 20-minute, 45-minute, 60-minute, 90-minute, and 3-hour (180-minute).
Construction | One-piece assembly with factory-welded, ground, and finished corners |
Wall Types | Masonry (CMU), concrete block, poured concrete |
Installation Timing | Before or during wall construction (set in place, wall built around frame) |
Corner Connection | Factory welded and ground smooth |
Fire Rating Range | 20-minute, 45-minute, 60-minute, 90-minute, and 3-hour/180-minute |
Common Applications | Stairwells, corridors, high-security areas, exterior openings, rated walls |
Shipping | Ships as one piece; requires careful handling to prevent damage |
Drywall Slip-On (Wrap-Around) Frames
A drywall slip-on frame, also called a wrap-around frame, is a type of knocked down frame specifically designed for drywall partitions. The frame profile includes backbends that wrap around both sides of the finished drywall, creating a clean appearance without exposed fasteners on the face. Slip-on frames install after the drywall is hung and finished, which allows the drywall contractor to complete their work without coordinating around pre-set frames.
The throat dimension of a slip-on frame must match the total wall thickness exactly, including the studs and drywall on both sides. Standard throat dimensions correspond to common wall constructions. Slip-on frames are available in fire-rated configurations at 20-minute, 45-minute, 60-minute, and 90-minute levels. Assemblies requiring a 3-hour (180-minute) rating must use welded masonry frames.
Construction | Three-piece KD frame with wrap-around backbends for drywall |
Wall Types | Drywall over metal studs, drywall over wood studs |
Installation Timing | After drywall is hung and finished |
Corner Connection | Interlocking tabs and slots, same as standard KD |
Fire Rating Range | 20-minute, 45-minute, 60-minute, and 90-minute |
Common Applications | Commercial interiors, tenant improvements, office build-outs, healthcare |
Throat Sizing | Must match exact wall thickness (e.g., 4-7/8” for 3-5/8” studs with 5/8” drywall each side) |
Frame Type Comparison
The following table provides a side-by-side comparison of the three primary frame types to help identify which frame construction is appropriate for a given wall type, installation sequence, and fire rating requirement.
Characteristic | Knocked Down (KD) | Welded | Drywall Slip-On |
Pieces | Three (head + two jambs) | One (factory welded) | Three (head + two jambs) |
Primary Wall Type | Drywall or masonry | Masonry or concrete | Drywall only |
Install Timing | After wall is complete | Before/during wall build | After drywall is finished |
Corner Strength | Mechanical interlock | Welded (highest rigidity) | Mechanical interlock |
Max Fire Rating | 3-hour/180-min (masonry) | 3-hour/180-min | 90-minute |
Shipping Profile | Flat-packed | One piece | Flat-packed |
Renovation Use | Suitable | Difficult (one piece) | Ideal for tenant improvement |
Cost | Moderate | Higher (welding + shipping) | Moderate |
Frame Profiles and Configurations
Hollow metal frames are manufactured in a range of profiles to accommodate different wall thicknesses, door configurations, and application requirements. The frame profile determines how the frame interfaces with the wall, the door, and the hardware. The following sections describe the key profile variations available in commercial door frames.
Single Rabbet vs. Double Rabbet
The rabbet configuration determines whether the frame accommodates a single door or a pair of doors. Single rabbet frames have one stop and one rabbet, designed for a single door leaf. Double rabbet frames have a center stop with rabbets on both sides, allowing two door leaves to close into the same frame. Double rabbet frames are used for pairs of doors, including those with an astragal or coordinator.
Single Rabbet | One stop, one door leaf. Standard for single-door openings in offices, patient rooms, storage rooms, and similar applications. |
Double Rabbet | Center stop with rabbets on both sides. Required for pairs of doors. Used in corridors, conference rooms, and wide openings. |
Standard Frame Depths
Frame depth (jamb depth) must match the total wall thickness exactly. The following table lists common frame depths and their corresponding wall constructions. When ordering, verify the actual wall thickness on-site before specifying the frame depth.
Frame Depth | Typical Wall Construction |
4-3/4” | 3-5/8” metal studs + 1/2” drywall each side |
4-7/8” | 3-5/8” metal studs + 5/8” drywall each side |
5-3/4” | 4” metal studs + 7/8” plaster each side |
6-3/4” | 6” metal studs + 5/8” drywall each side (or CMU with furring) |
8-3/4” | 8” CMU block (nominal) |
Frame Gauge (Steel Thickness)
Hollow metal frames are manufactured from steel sheet in standard gauges. The gauge determines the thickness and structural capacity of the frame. Heavier gauges (lower numbers) provide greater strength and are required for higher fire ratings and heavy-duty applications. The following table summarizes the standard gauges used in commercial frames.
Gauge | Nominal Thickness | Typical Application |
18 gauge | 0.042” | Standard commercial interior, drywall frames up to 90-minute rating |
16 gauge | 0.053” | Heavy-duty commercial, high-traffic corridors, fire-rated masonry frames |
14 gauge | 0.067” | Maximum duty, high-security, blast-resistant, 3-hour/180-minute rated openings |
Frame Anchoring Methods
The anchoring method secures the door frame to the surrounding wall structure. The correct anchor type depends on the wall construction (drywall, masonry, concrete), the frame type (KD, welded, slip-on), and whether the opening is fire-rated. Using the wrong anchor type or failing to install anchors correctly can result in a frame that shifts under use, fails a fire inspection, or cannot support the weight of the door and hardware. The following sections describe the standard anchoring methods used in commercial door frame installation.
Base Clips (Floor Anchors)
Base clips secure the bottom of each jamb to the floor. They are used with both KD and drywall slip-on frames in stud wall applications. The clip attaches to the base of the jamb and is fastened to the floor with concrete screws or expansion anchors, depending on the floor material. Base clips prevent the jamb from shifting laterally at the floor line.
Location | Bottom of each jamb, at floor level |
Wall Types | Drywall over metal studs, drywall over wood studs |
Frame Types | Knocked down, drywall slip-on |
Fastener | Concrete screws (concrete floor) or wood screws (wood subfloor) |
Fire-Rated Use | Required on fire-rated drywall frames at 20-min, 45-min, 60-min, and 90-min levels |
Compression Anchors
Compression anchors are built into the top of each jamb on drywall slip-on frames. A flange on the back of the jamb presses against the wall stud when the frame is installed, creating friction that holds the upper portion of the jamb in position. Compression anchors work in conjunction with base clips or base screws to fully secure the frame. They do not require additional fasteners at the anchor point itself.
Location | Top of each jamb, behind the wall surface |
Wall Types | Drywall over metal studs |
Frame Types | Drywall slip-on (wrap-around) |
Fastener | None required; friction-based compression against the stud |
Fire-Rated Use | Acceptable for drywall frames rated at 20-min, 45-min, 60-min, and 90-min |
T-Anchors (Masonry T-Anchors)
T-anchors are flat, T-shaped steel tabs that are spot-welded or factory-attached to the back of a welded frame at specified intervals. When the masonry wall is built around the frame, the T-anchors embed in the mortar joints between courses of block. This permanently locks the frame into the masonry wall. T-anchors are the standard anchoring method for welded frames in CMU (concrete masonry unit) walls.
Location | Back of each jamb and the head, at mortar joint intervals (typically 24” on center) |
Wall Types | Masonry (CMU), concrete block |
Frame Types | Welded frames |
Fastener | Embedded in mortar joints during wall construction |
Fire-Rated Use | Required for fire-rated masonry openings at all levels: 20-min, 45-min, 60-min, 90-min, and 3-hour/180-min |
Wire Anchors
Wire anchors are looped steel wire ties that are factory-attached to the back of a welded frame. Like T-anchors, they embed in the mortar joints as the masonry wall is built. Wire anchors provide a flexible connection that allows minor adjustment during wall construction. They are commonly specified as an alternative to T-anchors in CMU wall applications.
Location | Back of each jamb and the head, at mortar joint intervals |
Wall Types | Masonry (CMU), concrete block |
Frame Types | Welded frames |
Fastener | Wire loops embedded in mortar joints during wall construction |
Fire-Rated Use | Acceptable for fire-rated masonry openings at all levels: 20-min, 45-min, 60-min, 90-min, and 3-hour/180-min |
Existing Masonry Anchors (Expansion Bolts and Tap-Ins)
When a frame must be installed into an existing masonry wall after construction is complete, T-anchors and wire anchors cannot be used because there are no open mortar joints. In these cases, expansion bolts or tap-in anchors are drilled through the frame and into the masonry. These anchors are common in renovation projects where a new door opening is cut into an existing block wall or where a frame is being replaced.
Location | Through the frame into the masonry at specified intervals |
Wall Types | Existing masonry (CMU), concrete block, poured concrete |
Frame Types | KD frames, welded frames (retrofit) |
Fastener | Expansion bolts, sleeve anchors, or tap-in anchors drilled into masonry |
Fire-Rated Use | Verify with the AHJ; acceptable at all five rating levels (20-min, 45-min, 60-min, 90-min, 3-hour/180-min) when properly specified |
Stud Anchors (Wood and Steel Stud)
Stud anchors secure the frame directly to the wall studs through the backbend or the throat of the frame. In metal stud walls, screws pass through the frame and into the stud flange. In wood stud walls, screws or nails fasten through the frame into the wood member. Stud anchors are used at multiple points along each jamb and across the head to distribute the load and prevent racking.
Location | Through backbend or throat into wall studs at intervals (typically 2-3 per jamb) |
Wall Types | Drywall over metal studs, drywall over wood studs |
Frame Types | Knocked down, drywall slip-on |
Fastener | Self-tapping screws (metal studs) or wood screws (wood studs) |
Fire-Rated Use | Required on fire-rated drywall frames at 20-min, 45-min, 60-min, and 90-min levels |
Anchoring Method Comparison by Wall Type
The following table summarizes which anchoring methods are used with each wall construction type, helping identify the correct anchor for a given project condition.
Anchor Type | Drywall / Metal Stud | Drywall / Wood Stud | New Masonry (CMU) | Existing Masonry |
Base Clips | Yes | Yes | No | No |
Compression Anchors | Yes (slip-on only) | No | No | No |
T-Anchors | No | No | Yes | No |
Wire Anchors | No | No | Yes | No |
Expansion Bolts | No | No | No | Yes |
Stud Anchors | Yes | Yes | No | No |
Fire Rating Requirements for Frames
Fire-rated door assemblies require that the frame, door, hardware, glass (if any), and louvers (if any) all carry matching fire labels at the required rating level. The frame fire rating is determined by the wall construction, the frame type, and the Authority Having Jurisdiction (AHJ) requirements. The following table summarizes the maximum fire ratings achievable with each frame type.
Fire Rating Level | KD Drywall Frame | KD Masonry Frame | Welded Masonry Frame | Drywall Slip-On Frame |
20-minute | Yes | Yes | Yes | Yes |
45-minute | Yes | Yes | Yes | Yes |
60-minute | Yes | Yes | Yes | Yes |
90-minute | Yes | Yes | Yes | Yes |
3-hour (180-minute) | No | Yes | Yes | No |
Drywall slip-on frames and KD drywall frames can achieve fire ratings up to 90 minutes. Assemblies requiring a 3-hour (180-minute) rating must use masonry frames, either KD or welded. CDF labels every fire-rated assembly before shipping. Verify all code requirements with project specifications and the Authority Having Jurisdiction (AHJ).
Selecting the Right Frame Type
Frame selection depends on four primary factors: wall construction, installation timing, fire rating requirements, and project budget. The following decision points help narrow the selection to the correct frame type for a given opening.
- Wall is drywall over metal or wood studs, and the wall is already built: Use a knocked down (KD) frame or drywall slip-on frame.
- Wall is masonry (CMU) and is being built new: Use a welded frame with T-anchors or wire anchors set during wall construction.
- Wall is existing masonry and a new opening is being cut or a frame is being replaced: Use a KD masonry frame with expansion bolt anchors.
- Opening requires a fire rating of 90 minutes or less in a drywall wall: A KD drywall frame or drywall slip-on frame will meet the requirement.
- Opening requires a 3-hour (180-minute) fire rating: A masonry frame (KD or welded) is required. Drywall frames cannot achieve this rating.
- Project is a tenant improvement or renovation with finished walls: A drywall slip-on frame is the most practical choice, as it installs without disturbing the existing wall finish.
Configure Your Frame Assembly
CDF’s ProBuilder tool allows contractors and facility managers to configure frame assemblies online. During configuration, ProBuilder guides frame type selection based on wall construction, displays compatible anchoring options, and calculates throat dimensions automatically. ProBuilder provides instant pricing for complete door, frame, and hardware assemblies.
For assistance selecting the correct frame type and anchoring method for your project, call (855) 769-9895 or email sales@cdfdoors.com. CDF’s sales team is available Monday through Friday, 7:30 AM to 4:30 PM CT.
Frequently Asked Questions
What is the difference between a knocked down frame and a welded frame?
A knocked down (KD) frame ships as three separate pieces (head and two jambs) that are assembled on-site using interlocking tabs and slots. A welded frame ships as a single piece with factory-welded corners. KD frames install after the wall is built and are used in drywall and masonry walls. Welded frames are set before or during masonry wall construction. Welded frames offer higher corner rigidity and are the standard for masonry walls and high-fire-rating applications.
What is a drywall slip-on frame?
A drywall slip-on frame, also called a wrap-around frame, is a three-piece knocked down frame designed to wrap around a finished drywall opening. The frame profile includes backbends that grip both sides of the drywall, creating a finished appearance without exposed fasteners. Slip-on frames install after the drywall is hung and finished, making them the standard choice for commercial interior applications in metal stud walls.
What fire ratings are available for hollow metal door frames?
Hollow metal frames are available in five fire rating levels: 20-minute, 45-minute, 60-minute, 90-minute, and 3-hour (180-minute). Drywall frames (KD and slip-on) can achieve ratings up to 90 minutes. Masonry frames (KD or welded) can achieve the full range up to 3 hours (180 minutes). All components in a fire-rated assembly, including the door, frame, hardware, glass, and louvers, must carry matching fire labels.
What does the throat dimension of a frame mean?
The throat is the opening between the backbends of the frame, and the throat dimension must match the total wall thickness exactly. For example, a wall with 3-5/8” metal studs and 5/8” drywall on each side has a total thickness of 4-7/8”, requiring a frame with a 4-7/8” throat. Ordering a frame with the wrong throat dimension results in a frame that does not fit the wall and cannot be corrected on-site.
What type of anchors are used with masonry door frames?
New masonry walls typically use T-anchors or wire anchors that are factory-attached to the frame and embedded in the mortar joints during wall construction. Existing masonry walls require expansion bolts or tap-in anchors drilled through the frame into the block or concrete. The anchor type must be specified at the time of order because T-anchors and wire anchors are factory-attached before shipping.
What is the difference between single rabbet and double rabbet frames?
A single rabbet frame has one stop and one door-closing surface, designed for a single door leaf. A double rabbet frame has a center stop with rabbets on both sides, designed for a pair of doors. The rabbet configuration is determined by whether the opening has one door or two. Single rabbet frames are used for standard single-door openings; double rabbet frames are required for pairs of doors in corridors, conference rooms, and other wide openings.
How do I determine the correct frame depth for my wall?
Measure the total wall thickness at the door opening, including studs, drywall or plaster on both sides, and any furring strips. The frame depth (jamb depth) must match this total dimension exactly. Common frame depths include 4-3/4” (3-5/8” studs + 1/2” drywall each side), 4-7/8” (3-5/8” studs + 5/8” drywall each side), and 6-3/4” (6” studs + drywall). Measure in at least two places, as walls can vary in thickness due to construction tolerances.
Can a knocked down frame be used in a masonry wall?
Yes. KD frames are available in masonry configurations that install into existing masonry walls using expansion bolts or sleeve anchors. KD masonry frames are commonly used in renovation projects where a new opening is cut into an existing block wall. KD masonry frames can achieve fire ratings up to 3 hours (180 minutes) when properly specified and anchored.
About This Guide
This reference guide is based on CDF Distributors’ product specifications, fabrication standards, and field knowledge developed through commercial door and frame distribution from its Nashville, Tennessee facility. The frame terminology, type classifications, and anchoring methods described in this guide follow industry standards referenced in ANSI/SDI A250.8 (Recommended Specifications for Standard Steel Doors and Frames) and NFPA 80 (Standard for Fire Doors and Other Opening Protectives).
For questions about frame types, anchoring methods, or to configure a frame assembly for your project, contact CDF at (855) 769-9895 or sales@cdfdoors.com. Configure your assembly online at cdfdistributors.com using ProBuilder.
