Commercial scope
Metal stud framing
Light-gauge cold-formed steel is the framing of virtually every commercial interior in California — non-combustible, dimensionally stable, and the basis of nearly every tested fire-rated and sound-rated wall assembly there is. It is also a trade with a handful of details that decide whether a building cracks in year two, and most of them are invisible once the board is on.
This page is those details.
01
The members, and how they are named
A steel-framed wall is a stud — a C-shaped member with a web, two flanges and, on structural members, a return lip — seated top and bottom in track, which is a U-shaped runner with a web and two legs and no lip. The stud carries the panel. The track locates the studs and transfers load into the floor and the structure above.
The trade does not really speak in gauges anymore. Every cold-formed member carries a four-part designator: web depth in hundredths of an inch, a type letter, flange width in hundredths of an inch, then base steel thickness in mils. So 362S162-33 is a 3-5/8" web by 1-5/8" flange C-shaped stud in 33 mil steel. The type letters are S for stud, T for track, U for cold-rolled channel, F for furring channel and L for angle.
A mil is one thousandth of an inch of base steel, measured before galvanizing. Standard non-structural web depths are 1-5/8", 2-1/2", 3-5/8", 4" and 6", with 8" common in shaft and structural work. Standard non-structural flange width is 1-1/4"; track legs come in 1-1/4" and 1-1/2", and deflection tracks run 2", 2-1/2" and 3" legs. Wider flanges buy screw-landing tolerance on long straight runs and resist stud rotation — a difference the owner never sees and the painter always does.
Punchouts have geometry rules, and they have to line up
The standard sets punchout spacing at not less than 24" on center, width not greater than half the member depth or 2-1/2" whichever is less, length not exceeding 4-1/2", and the first punchout not less than 12" from the end of the member.
In the field the thing that matters is alignment. Studs set with punchouts out of line force the electrician and the plumber to drill the web, which is a modification to an engineered member. Lining up punchouts is free at framing time and expensive afterwards.
Coating
Both the product standard and the framing standard require a minimum G40 galvanized coating or equivalent corrosion resistance. G60 and G90 exist and get specified for exterior, high-humidity and coastal exposure — which is a live question a mile from the water in North County, and a question worth asking at submittal rather than assuming.
Mil, gauge and color code
The conversion that matters on a submittal. Color codes are the ASTM C645 marking system stamped on the member.
| Mil | Design t | Gauge | Color |
|---|---|---|---|
| 18 mil | 0.0188" | 25 ga | none |
| 27 mil | 0.0283" | 22 ga | black |
| 30 mil | 0.0312" | 20 ga drywall | pink |
| 33 mil | 0.0346" | 20 ga structural | white |
| 43 mil | 0.0451" | 18 ga | yellow |
| 54 mil | 0.0566" | 16 ga | green |
| 68 mil | 0.0713" | 14 ga | orange |
| 97 mil | 0.1017" | 12 ga | red |
The two 20-gauges. 30 mil is 20 ga drywall. 33 mil is 20 ga structural. They are not interchangeable, they do not price the same, and they sit on opposite sides of the non-structural line. A spec that just says “20 gauge” is ambiguous and should generate an RFI.
02
Structural and non-structural are two different products
This is the distinction that separates a commercial framer from a residential drywaller, and it is drawn by load, not by feel.
A member counts as non-structural only if the transverse out-of-plane load on it is no more than 10 lb/ft² — 15 lb/ft² is permitted for pressurized plenums and elevator shafts — and the superimposed system axial load, excluding sheathing, is no more than 100 lb/ft, and the superimposed load on any one member is no more than 200 lb.
Cross any of those and the wall is no longer a drywall stud wall. A partition that picks up a beam, a wall carrying a header over a rated opening, a stud wall supporting a mechanical unit, an exterior backup wall taking wind — that is cold-formed steel structural framing, and it lives under a different product standard and a different design standard.
The other practical difference is who designs it. Non-structural partitions are specified prescriptively: the architect picks a depth, a thickness and a spacing off a manufacturer’s limiting-height table. Structural cold-formed steel is a delegated design — the engineer of record writes a performance spec, a specialty CFS engineer designs the members and connections and seals shop drawings, and the whole thing goes to the building department as a deferred submittal. It is too late to discover you need shop drawings the week you mobilize, which is why we ask about it at bid time.
The limiting-height table is not one number
A limiting-height table is a function of three inputs: the design lateral load, the allowable deflection, and the stud spacing. The same stud at the same spacing gives wildly different allowable heights at L/120 and at L/360 — and L/360 is what rigid finishes like tile, stone and glass require. A framer who reads the finish schedule against the partition schedule and matches the deflection criterion is doing engineering-adjacent work. One who just uses 20 gauge is guessing.
Two further traps in those tables. First, published tables assume a bracing condition — if the table says braced at 48" on center and the bridging does not get installed, the wall does not meet the height it was bid to. Second, composite tables credit the gypsum board as bracing and non-composite tables do not, so walls that are open on one side — chases, backs of millwork, partial-height partitions — generally cannot use the composite values.
EQ studs, and being honest about them
Most of the current non-structural stud market is EQ product: members rolled from thinner base steel that use higher-strength steel and modified geometry to deliver equivalent bending capacity, qualified through evaluation reports with their own published limiting-height tables rather than by straight dimensional compliance.
The sources genuinely disagree here, and it is worth saying so. The product standard sets an 18-mil floor on base steel; EQ products come in under that and are approved by an alternate path. Both statements are true. Where a specification names the product standard with no allowance for an evaluation report and the estimator buys EQ, that is a real submittal fight. We read the spec and submit what the spec calls for. Separately, on fire-rated work, many non-load-bearing listed designs call out generic studs defined only by minimum dimensions and thickness, while EQ studs have to bear a certification mark because their base steel is thinner than the generic minimum — another reason to read the listing rather than assume.
03
The head of wall: why a partition is never framed tight to the deck
If you read one section of this site, read this one. It is the detail most commonly blown in the field, it is blown by good framers with residential habits, and the damage it causes shows up long after everyone has been paid.
A non-load-bearing partition is designed to carry its own weight and a modest out-of-plane pressure. Nothing else. The floor or roof structure above it, meanwhile, is designed to move — beams and slabs deflect downward under live load, lift under uplift, and sway laterally in a seismic event, and the code permits meaningful movement in those members. Frame the partition tight to the deck and screw the studs off at the top, and you have quietly turned the wall into a column: the structure’s movement is transferred straight into studs that were never designed to receive it. You then see the result in a predictable order. A horizontal crack opens along the length of the partition just below the deck. Diagonal cracks run out of the door corners. The studs bow or crush at the track, the door goes out of square and stops latching, and if the wall is rated, the head-of-wall joint — a listed fire-resistant joint system tested for a specific amount of movement over a specific number of cycles — is no longer performing as listed, because a rigid connection either prevents the movement the joint was tested to accept or delivers it in a pattern the test never covered. The fix is not caulk and it is not a heavier stud. It is a deliberately detailed gap at the top of the wall, built one of two ways: deep-leg deflection track, where the studs are cut short, set inside the long legs and deliberately left unfastened so they slide as the structure moves; or slotted deflection track, where the stud is fastened — but with a wafer-head screw riding the middle of the slot, so the connection holds the stud from rotating or walking while still letting it travel. The gap is not eyeballed. The manufacturer publishes it with the track: on ClarkDietrich’s deep-leg schedule, a 2" leg wants 1/2" between the end of the stud and the track web, a 2-1/2" leg wants 3/4", and a 3" leg wants 1". Screwing a stud tight to a deflection track defeats the entire system, and it is the instinct every framer trained on wood brings to the job, because in wood framing you always fasten the stud to the plate.
What goes wrong, in order
- A horizontal crack opens along the full length of the partition, just below the deck.
- Diagonal cracks radiate out of the door corners as the opening racks.
- The studs bow out of plane or crush at the track. An 18 mil stud has almost no axial capacity.
- The door frame goes out of square, and the door stops latching.
- In a rated wall, the head-of-wall joint is no longer being built the way it was listed.
- In a seismic event the partition becomes an unintended load path into a structure that was never designed to receive it there.
The four ways the gap gets built
Deep-leg slip track. An outer track with a long leg is fastened to the deck, the studs are cut short and set inside it, and the studs are not fastened to the deflection track. Gravity and the gypsum hold the wall plumb; the studs slide inside the legs as the structure moves.
Slotted deflection track. The track legs carry vertical slots and the studs are attached with a wafer-head screw through the middle of the slot, so the stud can travel the length of the slot. Minimum #8 wafer-head screws for that connection. There is a real secondary benefit: because a slotted connection restrains stud rotation, it can eliminate the need for lateral bridging in the wall, which a knowledgeable estimator can price.
Deflection and drift clips. A separate clip — one solid leg to the substrate, one slotted leg to the stud — takes the movement instead of the track. Used where the head condition is irregular, at structural steel, or where larger movement is required.
Rip track and extended-range systems. For large movement. Slotted track systems are generally limited to roughly 2" total, an inch of compression and an inch of extension; rip-track systems can accommodate up to about 4", which is what data center work tends to require.
In a rated wall, the joint is its own listed system
A deflection joint in a fire-rated wall is not a gap with caulk in it. It is a listed fire-resistant joint system in its own right, tested to its own standard and required by code wherever joints occur in or between fire-resistance-rated assemblies. It is built either field-installed — mineral wool compressed to a specified ratio with an elastomeric or intumescent sealant at a specified depth — or with a factory-integrated track carrying an intumescent strip.
The designations are readable once you know the convention. The first two letters are the location: HW for head of wall, BW for bottom of wall, WW wall to wall, FF floor to floor, FW floor to wall. The letter after that is S for static or D for dynamic, and dynamic means movement-rated. The numeric range encodes the joint width. A dynamic joint is rated for a specific percentage of movement over a specific number of cycles, and that is the number that gets destroyed when the head of wall is made rigid in the field to solve a sealing problem.
Deep-leg gap schedule
Published with the track by ClarkDietrich. The gap is the distance from the end of the stud to the web of the deflection track.
- 2" leg1/2" gap
- 2-1/2" leg3/4" gap
- 3" leg1" gap
On a deep-leg deflection track the studs are not fastened to the track.
Nothing on this page replaces the approved drawings, the listed design named in the specification, or the authority having jurisdiction. Where a detail on the drawings and a manufacturer’s published requirement disagree, we write the RFI rather than pick one.
04
Bracing and bridging are two different jobs
Bridging — bracing the stud itself
A C-shaped member is torsionally weak. Unbraced, it twists under load and its capacity drops. Bridging stops the individual stud from rotating about its own axis and from buckling about its weak axis.
It is done with 3/4" or 1-1/2" cold-rolled channel threaded through the stud punchouts and clipped to each stud, or with flat strap applied to the flanges. Spacing comes from the limiting-height table the wall was designed to — the standard published tables assume bracing at 48" on center.
Watch the footnotes. Where a stud bears on something, some configurations require web stiffeners at the bearing point.
Bracing — holding the partition to the structure
A completely different problem. A partition that stops at the ceiling, or runs up past a lay-in ceiling to the deck, has to be braced back to the structure so it does not topple out of plane in an earthquake.
The classic detail is a diagonal kicker from the head of the partition up and back to the deck, joist or beam at roughly 45 degrees, alternating sides of the wall. Kickers are metal stud or cold-rolled channel where a compression-capable brace is needed — not wire.
The rule that is not negotiable: the partition’s bracing has to be independent of the suspended ceiling’s seismic bracing. The ceiling is not a brace and the partition is not a hanger.
05
California seismic bracing of partitions
The governing document is ASCE 7 Chapter 13, Seismic Design Requirements for Nonstructural Components, adopted by reference through the building code. The substantive requirement is simple to state: partitions that are tied to the ceiling, and all partitions over 6 feet tall, have to be laterally braced to the building structure.
The accepted methods:
- Splay wires. Two minimum 12-gauge wires at a maximum of 45 degrees from horizontal, in opposite directions, perpendicular to the partition, at a maximum of 8 ft on center.
- Rigid bracing. Minimum 25-gauge metal studs at a maximum of 45 degrees from horizontal, at a maximum of 8 ft on center, alternating sides.
- Hybrid. Connection to the ceiling suspension system with two 12-gauge splay wires at a maximum of 45 degrees plus a vertical strut at a maximum of 4 ft on center.
- Intersecting walls may substitute for rigid braces.
- Support by a suspended drywall ceiling, where that ceiling is flat and runs load-bearing wall to load-bearing wall.
There is an exemption, and all three parts of it have to be met at once: height no more than 9 feet, linear weight no more than 10 lb per foot of height, and horizontal seismic load no more than 5 psf. Most commercial partitions in this market miss it on height alone.
In the lower seismic design categories the ceiling system is not permitted to provide lateral support for walls at all; walls may only attach to the ceiling suspension where the connection lets the ceiling membrane move laterally with a specified clearance.
What changed, and why it matters right now
The 2025 California Building Code took effect on 1 January 2026, and ASCE 7 revised Chapter 13 substantially in its most recent edition — amplification factors, response coefficients, explicit height amplification based on the building’s seismic system, and updated ground-motion maps. The practical effect in California is that interior partitions that used to be covered by a prescriptive manufacturer limiting-height table can now need stamped engineering and upgraded connection detailing.
We are not going to publish a percentage for that increase, because the numbers in circulation are individual example calculations rather than code-published figures. The direction is not in doubt: seismic demand on interior partitions went up materially, and it is worth raising in preconstruction rather than discovering at plan check.
California runs a three-year code cycle and section numbers move between cycles. We build to the code edition in force for your project and the approved drawings for your project, and we do not quote section numbers at people from a website.
06
Backing and blocking
Small dollars, enormous callback risk. Every wall-mounted object needs somewhere to land, and it has to be in the wall before the board goes on. A missed backing means cutting open finished, painted, sometimes rated wall.
- Grab bars and accessible restroom fixtures — the ADA Standards and California Building Code Chapter 11B require the bar, its fasteners, its mounting device and the supporting structure behind it to resist 250 lb applied at any point, vertically or horizontally. In steel framing that means a continuous 16-gauge plate or strap across the studs, located and dimensioned from the accessibility elevations.
- Casework and millwork — the Architectural Woodwork Institute names 6" 16-gauge flat strapping as the acceptable backing in metal stud walls in place of wood blocking, and states plainly that it is installed by others. This is the single most common scope gap on a tenant improvement: if it is not in somebody’s contract it does not get installed, and the cabinet hanger finds out at hang time.
- Flat-screen displays and monitor arms — an articulating arm generates a moment load far larger than a static weight check suggests.
- Handrails and guards — these are structural. They carry code-prescribed loads and normally need a heavier plate or a dedicated member designed by the engineer of record.
- Toilet accessories, mirrors, shelves, wall-hung fixtures and carriers, and the chase framing that has to accommodate them.
- Medical and dental — x-ray heads and arms, monitor arms, casework, IV tracks, cubicle and privacy curtain tracks, handwash stations, sharps and glove-box holders.
- Fire extinguisher, AED and knox cabinets; wall-mounted fan coils, mini-split heads, louvers and access panels.
- Classroom work — marker boards, tack boards, projector mounts, speakers, display mounts and coat hooks. On a school job the anchorage of every one of those is reviewed work, not field discretion.
The backing plan
The professional move is a deliverable, not a memory. A marked-up floor plan and elevations produced in preconstruction, showing every backing location with its height and type, circulated to the GC and the affected trades for confirmation before framing starts.
The list above is the backing we coordinate, built from the drawings and the equipment schedules. It is trade practice and project-specific — it is not a code list, and we build it from your documents rather than from memory.
07
Soffits, furring, chases and radius walls
Soffits and bulkheads
A framed box hung from the structure — a horizontal member hung from above, vertical studs forming the face, a horizontal ceiling plane, cross-braced back to structure. In commercial work they conceal duct mains, sprinkler mains, conduit and structure, form light coves and valances, define retail and restaurant zones, and drop the ceiling over corridors and casework.
Two things separate a professional soffit from a rough one. It is hung from the structure, never from the ACT grid and never from the ductwork it conceals. And it is straight over distance — a sixty-foot soffit reads as a single line under linear lighting, and laser layout, tight bridging and consistent stud gauge are what make it read that way.
Furring
Furring creates a flat, plumb, screwable plane over something that is not: tilt-up concrete, CMU, existing plaster, an out-of-plumb structural wall. Either hat channel fastened directly to the substrate, which is cheap, thin and rigid, or furring studs where a cavity is needed for insulation or acoustic decoupling.
Warehouse and industrial tenant improvement work is largely furring: the interior face of the panel, the office box inside the shell, and the ceiling over it. And note that resilient channel and hat channel are not interchangeable acoustically, however similar they look on the truck.
Chase walls
Two parallel rows of studs with a void between, carrying plumbing stacks, large conduit runs, back-to-back fixtures and mechanical risers.
A true chase wall is a decoupled assembly and performs substantially better acoustically than a single-row wall — one published example puts the difference at 14 STC points. That decoupling is destroyed the moment the two rows get tied together with rigid bracing instead of the cross-bracing the tested design specifies.
If the chase wall is rated, the rating comes from a specific tested design. You cannot convert a rated single-row wall into a chase wall and keep the rating.
Curved and radius walls
Two independent constraints: what the framing can do and what the board can do. Framing is curved track, factory-curved or field-kerfed, with studs at tighter spacing than a flat wall so the surface does not develop flat spots between them.
Standard board has published minimum dry bending radii — roughly 15 ft for 5/8", 10 ft for 1/2", 7 ft for 3/8" and 5 ft for 1/4". Tighter than that takes a specialty product: high-flex board reaches radii as tight as about 7 inches, and there is a thin fire-rated radius board made specifically for 1- and 2-hour rated curved walls that reaches a minimum radius of about 2 feet.
That last point matters on a bid. A curved rated wall cannot be built out of whatever happens to bend.
Send us your plans
Partition schedule, ceiling details, project manual and the bid date. If the head-of-wall detail or the deflection criterion is ambiguous, you will hear about it during bidding rather than during framing.