Steel framing in Australian construction: cold-formed sections, gauges, and selection vs timber

TL;DR

Steel framing is cold-formed C-section studs, top plates, bottom plates, noggins, top-hat battens, and lipped-channel sections rolled from galvanised steel coil to lengths typically pre-cut by the frame manufacturer. It’s a complete alternative to timber wall framing across Class 1a houses, Class 2 low-rise apartments, and Class 3-9 commercial fit-outs, offering termite immunity, dimensional stability (no shrinkage, no twist), recyclability, and a clean shopfit-style site. Class 2 inter-tenancy separating walls and Class 5-9 commercial deep-stud walls move up in gauge and add fire-rated and acoustic-rated wall systems built around the same C-section product range. The trade-offs: thermal bridging (steel conducts heat 400× better than timber, requiring thermal-break detailing in the wall build-up), condensation risk on the cold-side flange (more critical in cool-climate housing), and a steeper learning curve for chippies who have to switch from nails-and-skilsaws to tek screws and grinders. Cold-formed steel design sits under AS/NZS 4600:2018 and the residential framing standard AS 3623:1993. The volume Australian brand is BlueScope TrueCore, supplied through frame-and-truss manufacturers (Steeline, Stramit, Bond Steel Frame) as pre-cut, pre-marked kits ready to assemble on site. Common stud BMT (base metal thickness) gauges: 0.55, 0.75, 1.00, and 1.15 mm.

What it is

Steel framing is cold-formed steel (CFS): thin galvanised steel coil that’s roll-formed into structural sections (C-section, top-hat, lipped channel, etc.) at the manufacturer’s plant. Cold-forming is the process: the steel is bent through a series of rollers to create the section profile without heat. The result is a high-strength-to-weight ratio section with dimensional consistency well beyond what sawn timber achieves.

Two terms to keep separate:

Cold-formed steel (CFS): the wall framing studs, plates, and battens. Thin gauge (typically 0.55 to 1.15 mm BMT).
Hot-rolled steel (HRS): the structural steel beams for spanning members (UB, UC, PFC). Thicker section, higher strength.

A typical residential build with steel framing uses CFS for the wall and ceiling framing, with HRS lintels and beams where the load exceeds CFS capacity.

The Australian standard for design is AS/NZS 4600:2018 (Cold-formed steel structures). The base steel coil is produced to AS/NZS 1397:2021 with a galvanised coating (typically Z275 or Z350 g/m2 zinc) that protects the section from corrosion through the building’s life.

Common sections

Section	Profile	Where used
C-section stud	C-shape with returned lips	Wall studs, vertical members
C-section top plate / bottom plate	C-shape	Horizontal wall plates
Top-hat batten	Hat-shape with two flanges	Wall and ceiling battens, fixing point for plasterboard
Lipped channel (sigma section)	Z or sigma-shape	Joists, purlins
Noggin (cold-formed)	C-shape cut to length	Horizontal bracing between studs
Wall plate angle (90° L-shape)	L-section	Wall-to-floor and wall-to-ceiling tie-in
Brace strap (flat plate or X-brace)	Flat strap	Wall racking resistance

C-section studs are designated by depth (height of the C in mm) and gauge (BMT in mm). A “90 × 0.75 C” is a 90 mm deep stud with 0.75 mm base metal thickness. Standard depths: 75, 90, 92, 100, 150 mm; standard gauges: 0.55, 0.75, 1.00, 1.15 mm.

BMT gauges and application

BMT (mm)	Typical use	Compared to timber
0.55	Internal partition walls, non-loadbearing	Lighter than 70 × 35 timber stud
0.75	Standard external wall studs in normal-load conditions	Equivalent to 90 × 35 timber stud
1.00	Higher-load external walls, longer spans, gable ends	Equivalent to 90 × 45 timber stud
1.15	Heavily loaded walls, two-storey lower walls	Beyond standard timber framing without engineer’s review

The gauge selection is driven by the engineer’s design or the manufacturer’s pre-engineered specification. A typical residential frame uses 0.75 BMT studs for most external walls, with 1.00 BMT at gable ends, lintels, and higher-load areas.

Galvanising and coatings

Coating	Where used
Z275 g/m2 galvanising	Standard internal and most external framing; ~37 μm coating
Z350 g/m2 galvanising	Higher-corrosion exposure (subfloor, splash zones)
TrueCore (BlueScope)	BlueScope’s branded Z275-equivalent product for residential framing; the volume market default
GalvSpan, ZAM (zinc-aluminium-magnesium)	Higher-corrosion specialty coatings for severe environments

The galvanised coating is what makes steel framing termite-immune and rot-resistant. A cut end exposes raw steel and must be touched up with cold-galv spray paint to restore the protective coating. On-site cuts without touch-up are a corrosion-defect waiting to happen.

Where steel framing is the right call

Termite-prone areas without chemical treatment: north Queensland, parts of NSW and WA where termite pressure is high and the builder prefers physical termite barriers over chemical-treated timber. Steel is termite-immune by definition.

Long-span clear-frame walls (open-plan layouts): steel handles longer spans between studs than timber at equivalent capacity, and the section is dimensionally consistent across the run.

Fire-rated separation walls: where the building requires FRL-rated walls (multi-residential, townhouse boundaries, garage-to-house), steel framing with plasterboard FRL detail is the standard solution.

Sustainable / recyclable building specifications: steel is recyclable indefinitely; the carbon footprint of steel framing (with high recycled content) is competitive with timber when end-of-life recycling is included.

Sites with limited timber supply or volatile timber pricing: steel pricing has been more stable than timber through the 2020s. Some volume builders have moved to steel framing partly for supply certainty.

Cyclonic and severe wind areas: cold-formed steel under AS/NZS 4600 has well-characterised performance at high wind loads; some specifiers prefer steel for C2 and C3 wind classifications.

Where steel framing is wrong

Routine standard-class residential where timber’s lower thermal conductivity matters: cool-climate housing in Victoria, Tasmania, and the southern highlands where thermal bridging through steel studs degrades envelope performance materially.
Owner-builder jobs with carpenter trades: chippies are trained on nails, skilsaws, and PVA glue. Switching to tek screws, grinders, and crimping tools needs training time and tool investment. Volume residential builders absorb this; one-off owner-builds don’t.
High-humidity warm-climate framing without condensation control: tropical and sub-tropical climates can see condensation on the cold (cavity) side of steel studs; warm interior air contacts the cold steel, water condenses on it, soaks the plasterboard or sarking. Detailing matters.
Existing-house renovations where the new framing has to integrate with timber: mixing steel and timber framing in the same wall introduces galvanic corrosion risk and detailing complexity.

Connections

Cold-formed steel framing uses a different fastener vocabulary than timber:

Fastener	What it does
Tek screw (self-drilling, hex-head)	Joins steel-to-steel, steel-to-timber; sizes 8g-10 mm
Pop rivet	Light fastening for non-structural connection (sarking, paper backing)
Crimping tool (manual or hydraulic)	Joint two C-sections without screws; common at top plate corners
Welded connection	Only by qualified welder; rare in residential, common in commercial
Wall plate angle	L-shape pre-formed angle that ties wall plates to floor or ceiling
Brace strap	Flat strap diagonally fixed across studs for racking resistance

The connection design comes from the manufacturer’s pre-engineered details, not from a per-job structural engineer (for typical residential framing). The manufacturer supplies a detail sheet with the kit showing every connection point.

Pre-cut, pre-engineered framing systems

Most Australian residential steel framing is supplied as a kit: the frame manufacturer (Steeline, Stramit, Bond Steel Frame, Multispan, others) receives the building’s CAD plan, runs it through an engineering and routing software (BlueScope STUDFORM, RoofRanger, etc.), cuts every section to length, marks each piece with its location, and delivers the kit on a truck.

The site team’s job is to assemble the pre-cut frame, not to fabricate from raw stock. This shifts the trade skill from carpenter to assembler. The frame raised in a single day on a residential build is typical.

Thermal bridging and condensation

The largest performance trade-off vs timber. Steel conducts heat roughly 400 times better than softwood. A steel stud at 600 mm centres in a wall with R2.0 batt insulation between the studs delivers an actual wall R-value materially below the nominal batt rating, because heat flows through the steel and bypasses the insulation.

The mitigation is thermal break detailing:

Thermal-break tape: a foam strip applied between the steel stud face and the external sheathing or sarking, breaking the conductive path
Continuous external insulation: rigid foam board (XPS, EPS, PIR) applied over the external face of the framing, sandwiching the steel between layers of insulation
Wider studs for thicker batt: 92 mm or 100 mm studs allow higher-R batts (R2.5, R3.0) to reduce relative thermal impact

For climates above zone 4 (most of Sydney, Brisbane, Perth) the thermal-bridging penalty is often acceptable. For colder zones (Melbourne, Hobart, alpine areas), explicit thermal-break detailing is needed to meet NCC NatHERS targets.

Common defects and on-site issues

Touch-up paint missed at cut ends: raw steel exposed on the cut; corrosion starts within months. Always touch up with cold-galv spray.
Mixed steel and timber framing in the same wall: galvanic corrosion at any wet contact; condensation differential. Avoid wherever possible.
Tek screws over-driven: the head strips out the steel; the screw spins. Underdriven: the head sits proud and catches the plasterboard during sheeting. Driver calibration matters.
Wrong gauge specified or supplied: 0.55 BMT used in external wall where 0.75 was engineered. Visible only by checking the printed marking on each stud.
Sarking and insulation pinched at studs: condensation barriers must be continuous across the framing; pinch-points let water track behind the lining.
Lintel undersized for opening width: steel lintels are typically a separate engineered element; using a standard stud as a lintel is non-compliant.
No noggins or bracing per the manufacturer’s detail: frame racks under wind load if the bracing schedule isn’t followed.
Cold-galv touch-up applied to a wet or contaminated cut: the paint doesn’t bond and falls off in service. Touch-up must be on a clean, dry cut surface.

Pricing (2026 indicative, ex-GST, supply only)

Component	Per linear metre or item
90 × 0.75 BMT C-stud	$5-8/m
90 × 1.00 BMT C-stud	$7-11/m
92 × 0.75 BMT C-stud (high-R wall)	$6-9/m
Top hat batten (35 × 35 BMT 0.55)	$2-4/m
Wall plate angle	$4-7/m
Brace strap (steel X-brace, supply)	$8-14/m
Tek screws (per 1000 hex-head)	$40-90
Cold-galv spray paint (400 ml)	$20-35
Pre-cut, pre-engineered residential frame (supply for 200 m2 house)	$25,000-45,000

Pre-cut frame supply is typically 5 to 15% more expensive than timber framing for the equivalent house, before considering trade-skill differences. Volume builders find the pre-cut speed and reduced waste make the premium acceptable.

Standards and references

Standards Australia, AS/NZS 4600:2018 Cold-formed steel structures. https://store.standards.org.au (verified 2026-05-13).
Standards Australia, AS/NZS 1397:2021 Continuous hot-dip metallic coated steel sheet and strip. https://store.standards.org.au (verified 2026-05-13).
Standards Australia, AS 3623:1993 Domestic metal framing. https://store.standards.org.au (verified 2026-05-13).
BlueScope, TrueCore Steel Framing product information. https://www.bluescopesteel.com.au (verified 2026-05-13).
Australian Building Codes Board, NCC 2022 ABCB Housing Provisions (steel framing references). https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions (verified 2026-05-13).