Most framing problems on commercial jobs are decided before the first stud is cut. A wall-type tag with the wrong gauge, a partition taller than its stud can carry, a deflection limit that suits drywall but not tile: these turn into RFIs, cracked finishes and change orders weeks later.
This guide is for structural engineers, general contractors and estimators who specify, price or build metal stud walls, and for anyone hiring light gauge steel framing contractors. It covers how light gauge drywall studs differ from structural studs, how to read flange widths, web depths and stud designations, which deflection limit protects which finish, and what the G40, G60 and G90 coatings mean. It ends with what to ask before you award the framing package.
It is written from the field by our team of steel stud framing contractors working on commercial projects across the Greater Toronto Area.
Light Gauge vs Structural Studs: 25 and 20 ga vs 18, 16 and 14 ga
Steel studs fall into two families. Non-structural studs (CSI 09 22 16, made to ASTM C645) carry only the wall’s own weight and the drywall, and resist modest sideways pressure. Structural studs (CSI 05 40 00, made to ASTM C955 and designed to CSA S136 in Canada) carry real loads: wind on exterior walls, floors and roofs on load-bearing walls, and heavy equipment.
Gauge numbers run backwards: the lower the number, the thicker the steel. Because gauge is an old and loose label, the industry now specifies thickness in mils (thousandths of an inch), which is what you’ll find printed on the stud.
| Gauge | Minimum thickness | Family | Typical commercial use |
|---|---|---|---|
| 25 ga | 18 mil (about 0.45 mm) | Non-structural | Interior partitions, furring, bulkheads |
| 20 ga (drywall) | 30 mil (about 0.75 mm) | Non-structural | Taller partitions, tile backing, door jambs, heavier fixtures |
| 20 ga (structural) | 33 mil (about 0.84 mm) | Structural, light duty | Short exterior walls, light curtain-wall backup |
| 18 ga | 43 mil (about 1.09 mm) | Structural | Exterior curtain-wall studs, jambs and headers |
| 16 ga | 54 mil (about 1.37 mm) | Structural | Tall exterior walls, load-bearing walls |
| 14 ga | 68 mil (about 1.73 mm) | Structural | Load-bearing light gauge structures, heavy headers |
The practical rule: use the lightest stud that meets height, load and deflection, then go heavier only where the wall needs it. Overspecifying 20 ga across a whole floor adds cost and makes walls stiffer, which can also hurt acoustic performance.
The EQ Stud Caveat
“Equivalent” or EQ studs are high-strength, often embossed or ribbed profiles sold as substitutes for 25 and 20 ga. They use thinner steel but are shaped to perform like the gauge they replace, and they can save cost and weight. The catch: an EQ stud is only equivalent where it has been tested to be. Before accepting one on a submittal, check three things: its limiting-height tables for your wall, any fire-rated listing the wall must match, and any acoustic test the design relies on.
Commercial Steel Stud Framing Dimensions: Flange Widths and Web Depths
A steel stud is a C-shaped channel. The web is the wide back of the C; its depth sets the wall thickness and most of the stud’s stiffness. The flanges are the two short legs the drywall screws into. The lips are the small return edges that stiffen the flanges.
| Web depth | Common uses |
|---|---|
| 1-5/8″ | Furring, chases, thin partitions |
| 2-1/2″ | Short partitions, furring walls |
| 3-5/8″ | The standard interior partition |
| 4″ | Partitions needing extra height or a deeper cavity |
| 6″ | Tall partitions, exterior walls, plumbing walls |
| 8″ and deeper | Tall exterior walls, headers, load-bearing walls |
Flanges are usually 1-1/4″ on non-structural studs and 1-5/8″ or wider on structural studs. A wider flange gives more stiffness and more room to fasten sheathing.
Reading a Stud Designation
Most manufacturers use the Steel Stud Manufacturers Association (SSMA) naming system, so one code tells you the whole profile. Take 600S162-54:
- 600: web depth of 6.00″
- S: stud with lips (T is track, U is channel, F is furring)
- 162: flange width of 1.62″ (1-5/8″)
- 54: thickness of 54 mils (16 ga)
Specifying by designation instead of by gauge alone removes most of the guesswork, and most of the RFIs.
Deflection Limits: L/240, L/360 and L/600
Every wall bends a little when it’s pushed: by people leaning on it, by air pressure from HVAC and elevators, or by wind on an exterior wall. A deflection limit caps how far the middle of the stud may bow, as a fraction of its height (L). The more brittle the finish, the stricter the limit.
| Limit | Maximum bow on a 12 ft wall | Typical finish it protects |
|---|---|---|
| L/240 | About 0.6″ | Gypsum board with paint or wallcovering |
| L/360 | About 0.4″ | Plaster, veneer plaster, ceramic tile |
| L/600 | About 0.24″ | Natural stone, masonry veneer, large-format tile and other brittle finishes |
A stricter limit means a stiffer wall: a deeper web, heavier gauge or closer stud spacing. That is why a single tile wall in a washroom can change the stud on that wall even when the rest of the floor stays at 25 ga.
Limiting Heights
Manufacturers publish limiting-height tables that combine all the variables: stud designation, spacing, lateral pressure and deflection limit. Interior partitions are commonly designed for a lateral pressure of 5 psf (about 0.24 kPa), with higher pressures near elevator shafts, stairwells and exterior openings where the spec calls for them. Find the wall height on the table and it tells you whether the specified stud works.
When a wall exceeds its limiting height, the usual fixes are tighter stud spacing, a deeper web, a heavier gauge, or bracing back to structure. Exterior walls and load-bearing walls go further, with engineered design and shop drawings stamped by a licensed engineer.
FROM THE FIELD
A few years back, we were building a designer showroom inside a warehouse, and some of the walls were nearly 20 ft high. The engineer wanted us to frame them at 6″ on centre to handle possible air pressure coming from the front door. Instead, we went with heavier 18 ga studs and stiffeners every 4 ft.
Corrosion Protection: G40, G60 and G90 Coatings
Steel studs are protected from rust by a zinc (galvanized) coating applied at the mill. The G-number is the coating weight to ASTM A653: G40 has 0.40 oz of zinc per square foot of sheet, counting both sides; G60 has 0.60 oz; G90 has 0.90 oz. More zinc means a longer life where moisture is present.
| Coating | Typical use |
|---|---|
| G40 (or an approved equivalent coating) | Interior non-structural framing in conditioned spaces |
| G60 | Structural framing, exterior walls behind a weather barrier, and areas with occasional moisture |
| G90 | High-humidity or wet areas, exterior soffits, parking garages, pools and coastal exposure |
Two things to watch on submittals. First, some interior studs use alternative coatings marketed as equivalent to G40; confirm they meet the specification. Second, a cut or drilled stud loses coating at the cut, which matters little indoors but matters in wet areas. Where moisture is a real risk, specify the heavier coating rather than relying on touch-up.
Fire Safety Advantages of Steel Framing
Steel is non-combustible. It doesn’t burn, it adds no fuel to a fire, and it doesn’t produce smoke. That makes it the default in buildings the Ontario Building Code requires to be of non-combustible construction, which includes most larger commercial buildings.
Steel does lose strength as it heats, which is why the stud alone never carries a fire rating. The protection comes from the gypsum board around it, built as a tested assembly. Steel’s job is to stay straight, stable and non-combustible while the board does the fire work. For how those assemblies are built and inspected, see our guide to 1-hour and 2-hour rated assemblies.
Steel framing brings other practical advantages too. It doesn’t shrink, twist or rot, so finishes stay crack-free. Its dimensions are consistent, so walls go up straight. It is recyclable, and it generates less site waste because studs can be ordered cut to length.
What Estimators Should Check on the Drawings
Most framing change orders could have been caught at takeoff. Before you price a commercial steel stud framing package, check:
- Every wall type has a full stud callout: depth, gauge (or mils) and spacing, not just “metal stud”
- Wall heights against limiting heights, especially lobbies, atriums, gymnasiums and walls running to a high deck
- The deflection limit for each finish, so tile, stone and plaster walls are framed stiffer
- Door and window openings: jamb studs, headers and any heavier-gauge requirements at frames
- Backing and blocking for casework, grab bars, TVs, dental and medical equipment, and wall-hung fixtures
- Head-of-wall details: whether partitions need deflection track below structure
- Coating requirements for wet or exterior areas
- Exterior or load-bearing framing that needs delegated engineering and stamped shop drawings
- EQ stud substitutions and whether the fire and acoustic listings still apply
Framing is only half the wall. Check the board side at the same time, because layer counts, Type X requirements and finish levels change both scope and schedule. Our commercial drywall board and finishing scope is priced alongside the framing for that reason. Head-of-wall framing is covered in our guide to slotted deflection track systems.
How to Vet Light Gauge Steel Framing Contractors
The lowest framing number is rarely the cheapest framing job. Before you award the package, ask light gauge steel framing contractors:
- How do you handle engineered framing? For exterior curtain-wall studs and load-bearing walls, the contractor should bring a licensed engineer to provide the design and stamped shop drawings, not leave it to the GC.
- Who reviews the drawings before you price? A good framer flags limiting-height problems, missing backing and unclear wall types at bid time, not after mobilization.
- How do you lay out? Laser or total-station layout keeps long corridors straight and openings where the drawings put them.
- What is your crew capacity? Ask how many framers they can put on your job, and whether the same crew carries through to board.
- What is your safety record? Ask for WSIB clearance, safety program details, and COR certification if your project requires it.
- Can we see similar work? Look for projects of the same type and height: high lobbies, exterior steel stud, or multi-storey load-bearing.
A contractor that frames and boards the same walls removes one more handoff. Fewer trades on a wall means fewer gaps between scopes, and one party responsible for the result.
Frequently Asked Questions
What is the difference between 25 gauge and 20 gauge steel studs?
25 ga studs are about 18 mils thick and suit most interior partitions. 20 ga drywall studs are about 30 mils thick: stiffer and stronger, so they’re used for taller walls, door jambs, tile backing and walls carrying heavier fixtures.
Is light gauge steel framing structural?
It can be. 25 ga and 20 ga drywall studs are non-structural. 18, 16 and 14 ga studs are structural and are used for exterior curtain walls and load-bearing light gauge buildings, designed by an engineer.
What deflection limit should I use for drywall?
L/240 is the common limit for gypsum board. Use L/360 for plaster and ceramic tile, and L/600 for stone, masonry veneer and other brittle finishes.
What is the difference between G40 and G90 galvanizing?
The amount of zinc. G90 carries more than twice the zinc of G40, so it lasts longer where moisture is present. G40 or an approved equivalent is common for dry interior framing; G90 suits wet, exterior and high-humidity areas.
How tall can a 3-5/8″ steel stud wall be?
It depends on gauge, spacing, lateral pressure and deflection limit. Check the manufacturer’s limiting-height tables for the exact stud and conditions; a heavier gauge or closer spacing extends the height.
Does stud gauge affect soundproofing?
Yes. Lighter 25 ga studs flex more and pass less vibration, so they usually test better acoustically than heavier studs. See our guide on how stud gauge affects sound.
Submit Structural Framing Plans for a Fast-Turnaround Takeoff
Send us your architectural and structural drawings. We’ll check every wall type against its height, load and deflection limit, flag missing backing and head-of-wall details, and return a full framing takeoff, with board and finishing priced alongside if you need them. Send Plans Today, and receive an itemized bid breakdown within 24 to 48 business hours. Speak with one of our team members, Call (416) 466-1476.
CSI 09 22 16 NON-STRUCTURAL METAL FRAMING