What Is a Welded (Factory-Welded) Frame?
A welded hollow metal frame — also called a standard welded frame or pressed steel frame — is fully assembled at the factory before it ships. The two jambs and the head are mitered, fitted together, and welded at the corners. The welds are then ground smooth and filled so the finished frame presents clean, tight corner joints with no visible seam. The frame ships as a complete, rigid, three-dimensional unit ready to be set in the rough opening.
Welded frames are the standard specified frame type in most commercial construction projects. They are the default choice for masonry construction and are also widely used in metal stud and wood stud wall applications where the frame is set before or during wall construction.
What Is a KD (Knock-Down) Frame?
A knock-down frame (KD frame) ships in three separate pieces: the two jambs and the head. The pieces are designed to be assembled in the field by snapping or screwing the components together on-site. KD frames are engineered with a profile that allows the head to interlock with the jambs mechanically, creating a structurally sound assembly when properly installed.
KD frames are most commonly used in drywall (metal stud) applications, which is why you will often hear them referred to as KD drywall frames. The drywall is finished first, and the KD frame is installed into the completed opening, wrapping around the finished wall on both sides. This sequence makes KD frames particularly valuable for renovation work where existing walls are already in place.
When to Specify a Welded Frame
Welded frames are the appropriate choice in the following conditions:
- New masonry construction — The frame is set in the rough masonry opening and the block or brick is built around it. The rigid welded unit maintains squareness during construction.
- New metal or wood stud construction — The frame is set and braced in the opening before drywall is applied. The stud framing is built to the frame, not around it.
- Wherever a perfect finished appearance is required — Welded corners are ground smooth and produce a cleaner, more monolithic appearance than assembled KD joints.
- Fire-rated assemblies where weld integrity is part of the listing — Some fire-rated frame configurations require a factory-welded unit to maintain the integrity of the rated assembly.
- Most commercial project specifications — Many architectural specifications default to welded frames unless the wall type specifically requires KD.
When to Specify a KD Frame
KD frames are the better choice — and sometimes the only practical choice — in these situations:
- Retrofit and renovation projects — When walls are already finished and the opening is complete, a welded frame cannot be installed without cutting into the wall. A KD frame assembles in place.
- Replacement of existing frames in occupied buildings — KD frames can be removed and replaced without major demolition, reducing disruption.
- Where shipping an assembled frame is impractical — Welded frames are large, rigid units that can be difficult to transport through finished corridors or elevator lobbies during renovation. KD pieces are flat and maneuverable.
- Drywall construction where the sequence requires frame-after-wall — Some construction sequences finish drywall before frames are set, making KD the specified frame type.
Cost Comparison: Unit Price vs. Total Installed Cost
KD frames typically carry a lower unit cost than equivalent welded frames. The manufacturing process is simpler — no welding, grinding, or finishing of corners — which reduces production labor and material per unit.
However, total installed cost is a more complete comparison. KD frames require field labor to assemble and align each unit, which adds time on the job site. Welded frames arrive ready to set, which reduces field installation time per opening. On large projects with many openings, the labor differential can offset or exceed the unit price difference. On retrofit jobs where KD is the only practical option, the comparison is moot.
When evaluating cost, consider: number of openings, accessibility of the installation area, available field labor rates, and whether the project is new construction or renovation.
HMF Express Makes Both
HMF Express manufactures both welded and KD hollow metal frames from our production facility. Our welded frames are available in standard single rabbet, double rabbet, and masonry T-frame profiles for a wide range of wall thicknesses and construction types. Our KD drywall systems are engineered for clean, accurate field assembly and are available in the same standard profiles and custom sizes as our welded line.
If you are unsure which frame type is right for your application, your HMF Express rep can help you evaluate the project conditions and recommend the appropriate product — before you order.