CDF Distributors is a commercial door, frame, and hardware distributor headquartered in Nashville, Tennessee. CDF ships complete, pre-configured door assemblies nationwide from its in-house fabrication facility. Configure your assembly online at cdfdistributors.com using ProBuilder, or contact CDF at (855) 769-9895 or sales@cdfdoors.com.

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What is the difference between a welded and a KD frame?

A welded frame is a one-piece unit with joints permanently welded at the factory. It is set in place before the wall is built, with the wall constructed around the frame. A KD (knockdown) frame ships in three pieces (two jambs and a head) and is assembled on site, installed into an existing wall opening. The two types are designed for different installation sequences.

Can a welded frame be installed in an existing opening?

In most cases, no. Welded frames are designed to be set before the wall is built. Installing a one-piece welded frame into an existing opening typically requires removing wall material above and beside the opening, which may not be practical or permitted. KD frames are designed for installation into existing openings.

Can a KD frame be used in new construction instead of a welded frame?

Yes, KD frames can be used in new construction, and they are common in steel stud and drywall partitions. However, in masonry construction, welded frames set before the wall is built provide a more rigid connection. The choice depends on the wall type, project specifications, and installation sequence.

Does frame type affect fire rating?

Both welded and KD frames can be fire-rated at 20-minute, 45-minute, 60-minute, 90-minute, and 180-minute levels. However, the specific fire listing is different for each frame type, and the installation requirements differ. The fire listing must match the actual frame type installed. It is important to note that KD frames for stud wall applications cannot be rated higher than 90 minutes.

What if a welded frame was already ordered for a KD opening?

If the welded frame has not been manufactured, it may be possible to change the order to a KD frame. If the welded frame has already been fabricated or shipped, a new KD frame will need to be ordered. The welded frame cannot be field-converted to a KD configuration.

Frequently Asked Questions

CDF's ProBuilder tool allows contractors and facility managers to configure complete door, frame, and hardware assemblies online. ProBuilder displays compatible options and provides instant pricing.

For assistance with your order, 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.

Configure Your Door Assembly

Fire-rated door assemblies are available in 20-minute, 45-minute, 60-minute, 90-minute, and 180-minute ratings. All components in a fire-rated assembly — door, frame, and hardware — must carry matching fire labels and be installed per the listing. Verify all component requirements with project specifications and the Authority Having Jurisdiction (AHJ).

A Note on Fire-Rated Assemblies

Welded and KD frames have different rough opening requirements because of their different installation methods. A KD frame requires a rough opening slightly larger than its outside dimensions to allow for assembly, shimming, and adjustment. A welded frame's rough opening is determined by the wall construction built around it.

If a project has rough openings sized for KD frames and welded frames are ordered (or vice versa), the dimensional mismatch creates installation problems. This is another reason to verify the frame type early in the specification process and confirm it matches the construction conditions.

On fire-rated openings, both frame types are available in 20-minute, 45-minute, 60-minute, 90-minute, and 180-minute ratings, but the fire listing for each type specifies different installation requirements and clearances. Using the wrong listing voids the fire rating.

Rough Opening Requirements Differ

A one-piece welded frame typically cannot fit through an existing opening or be positioned into an already-built stud wall where drywall is up. The frame's outer dimensions are larger than the clear opening, and the anchoring system is designed to be embedded during wall construction, not attached to an existing wall surface.

Conversely, specifying a KD frame for new masonry construction may result in a less rigid installation than the project requires. While KD frames can work in some new construction situations (particularly drywall partitions), they are not the standard choice for masonry walls where the wall is built around the frame.

When a welded frame arrives on site for an existing opening where it needs to wrap, or where a finished wall is in place, the installer faces two options: return the frame and order a KD replacement, or demolish and rebuild the wall to install the welded frame. Neither option is cost-effective.

Why the Wrong Frame Type Will Not Fit

The fundamental difference between welded and KD frames is the installation sequence relative to the wall construction:

Welded Frame Installation

Welded frames are set in place before the wall is built, or while a wall has exposed studs. They can also be used in pre-existing masonry wall openings where the frame is not required to wrap. The frame is braced plumb, level, and square, and then the wall is constructed around it — masonry is laid up to the frame, or studs and drywall are installed against the frame. The frame's anchors are embedded in the wall during construction. In pre-existing masonry applications, the welded frame simply slides into place within the walls rough opening, and it is anchored in place accordingly.

KD Frame Installation

KD frames are installed after the wall is built. The three pieces are carried through the existing opening and assembled in place. Anchors fasten the frame to the existing wall material. This makes KD frames the correct choice for renovation projects, existing buildings, and any situation where the wall is already in place.

Installation Sequence Differences

Welded frames are manufactured as one-piece units with joints permanently welded at the factory. The completed frame arrives on site as a single rigid assembly that maintains its square and plumb during handling and installation. Welded frames provide maximum rigidity and are the standard choice for masonry wall construction.

KD (knockdown) frames ship in three separate pieces — two jambs and one head section. These pieces are assembled on site by the installer, typically using clips, screws, or snap-fit connections at the joints. KD frames are designed to be installed into existing wall openings without requiring wall demolition.

Welded vs. KD Frame Construction

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Understanding the differences between welded and KD frames and why the wrong frame type will not fit

This guide answers: What Happens If Welded Frames Are Ordered for Knockdown Rough Openings