The Problem Nobody Budgets For: Wall Thickness That Does Not Match the Frame Order
This article is for commercial contractors, project managers, and facility construction teams who have encountered a hollow metal frame that does not sit flush because the actual wall came in thicker or thinner than the drawing dimension. It covers what adjustable throat frames are, when to specify them instead of a fixed-depth frame, and what conditions on real job sites make them worth the upcharge.
What Is Frame Throat Depth -- and Why It Must Match the Wall
Every hollow metal frame has a throat: the opening at the back of the frame through which it slides onto the partition. Standard hollow metal frame construction sets the throat size at exactly one inch less than the overall frame width, because each 1/2-inch backbend on either side of the frame consumes that space.
The relationship is simple but unforgiving:
- Throat too narrow: The frame cannot be fully seated over the wall. It sits proud, gaps open on both faces, and backbends do not contact the wall surface.
- Throat too wide: The frame is forced over a wall thinner than designed. The section bows inward toward the strike jamb, the hinge pin centerline shifts, and door clearance disappears -- the door binds or drags from day one.
There is no acceptable field fix for a frame installed in a wall it was not designed to fit. The frame must be right before the wall goes up, or before the frame goes in.
Where Variable Wall Thickness Actually Happens
Wall thickness variability is more common than most schedules acknowledge. Here are the conditions that routinely produce mismatches:
- Renovation and tenant improvement work -- existing CMU or concrete walls that were originally plastered, furred, or have accumulated layers of finish over decades
- Healthcare construction -- infection-control wall assemblies, lead-lined partitions for radiology suites, or fire-rated assemblies with added layers of type X gypsum board can exceed the nominal design thickness
- School and institutional buildings -- masonry corridor walls that were originally built at one dimension and later modified or patched
- Industrial facilities -- process walls, clean room assemblies, and chemical-resistant partition systems that specify non-standard panel thicknesses
- Mixed-use commercial -- demising walls between tenant spaces where both sides of the wall belong to different finish specifications
In any of these situations, the nominal dimension on the architectural drawing may not match the field dimension by the time the framer, insulator, and drywall crew are done.
What an Adjustable Throat Frame Does Differently
An adjustable throat frame -- sometimes called a variable-depth frame or slip frame -- is engineered to accommodate a range of wall thicknesses rather than a single fixed dimension. The frame section includes a telescoping or slip-fit back section that can be set to the actual wall depth in the field and locked in place before or during installation.
Key characteristics:
- Covers a defined range of wall thicknesses within one frame SKU -- verify the range with the manufacturer before ordering
- Eliminates the need to re-order a frame when field dimensions differ from design dimensions by a moderate amount
- Allows the same frame profile to be used across multiple openings in a project where wall thickness is not perfectly consistent
- Still requires the installer to set the frame plumb, level, and square -- adjustability in depth does not compensate for installation errors in other planes
Adjustable Throat vs. Fixed Depth: How to Make the Call
Not every project needs an adjustable throat frame. Use the following decision framework:
Specify a Fixed-Depth Frame When:
- Wall thickness is confirmed by field measurement before frame order -- not just the drawing
- New construction with a single, consistent partition type throughout the opening schedule
- The wall is masonry or CMU and dimensions are known to be stable
Specify an Adjustable Throat Frame When:
- Renovation work where existing wall thickness has not been verified or is inconsistent from opening to opening
- Wall assemblies involve multiple trades whose combined finish thickness is uncertain at the time of frame order
- Lead-lined, sound-rated, or specialty partitions where added layers are specified but exact build-up thicknesses are subject to change
- The project schedule does not allow time to remeasure, re-order, and wait for a replacement frame if the first order is wrong
- The owner or GC has flagged the partition type as a known variable on a past project
Installation Reality: What the Crew Needs to Know
Adjustable throat frames save re-orders, but they still require careful handling in the field:
- Measure the actual wall thickness at the rough opening before adjusting the frame -- measure at multiple heights, because drywall finish can be thicker at the floor or header than at mid-height
- Set spreaders at mid-height and at the base before anchoring -- spreaders hold the frame width while the wall is built up around it
- Lock the adjustment before anchoring -- a frame that slips during installation will produce the same bowing problem as a wrong-size fixed frame
- Check jambs for twist as the wall progresses -- plumb on the face does not guarantee plumb through the throat
- Confirm fire-rated assembly requirements -- if the opening carries a fire label, verify with the frame manufacturer that the adjustable throat design is available in the labeled configuration for your required rating
Coordination Points for the Hardware Schedule
Frame throat depth affects more than just how the frame fits the wall. Downstream hardware items depend on these dimensions:
- Soffit width changes with jamb depth -- a deeper frame has a wider soffit, which affects parallel arm closer brackets and bar-type coordinators
- Strike projection -- extended lip strikes may be required if an increased face dimension causes the latch to contact the jamb face before it reaches the strike pocket
- Threshold fit -- if the throat depth changes the frame's position relative to the floor, threshold dimensions need to be reconfirmed
Communicate confirmed frame dimensions to your hardware supplier before finalizing the closer arm style, strike selection, and any threshold or seal package. DoorwaysPlus carries hollow metal frame hardware, including closers from Norton, Hager, and Corbin Russwin, thresholds and seals from Pemko, and a full range of frame trims that can be coordinated to your actual frame profile.
Bottom Line for Specifiers and Contractors
A hollow metal frame ordered to a drawing dimension and installed in a wall that turned out to be different is one of the most avoidable problems in commercial door work. Adjustable throat frames exist precisely for the job sites where wall thickness cannot be guaranteed until the trades are done -- renovations, specialty partitions, multi-layer fire or acoustic assemblies. Spec them where variability is a known risk. Measure before you order when it is not.
Need help selecting the right frame profile or coordinating the hardware package for a variable-wall project? Contact the team at DoorwaysPlus.com -- we help contractors, facility teams, and architects get the frame and hardware combination right the first time.