chalkline. Snap the line. Build to it.
regulation Compliance and regulation 4 min read

AS/NZS 4600 (cold-formed steel): the design code behind steel framing

AS/NZS 4600:2018 is the design standard for cold-formed steel structures: residential steel frames, trusses, purlins. Distinct from AS 4100 (hot-rolled).

By Dan Waring. Last updated 16 May 2026. Verified 16 May 2026.

Ask Chalkline about this →

In plain English

AS/NZS 4600:2018, Cold-formed steel structures, is the joint Australia/New Zealand design standard for cold-formed steel structures: residential and light-commercial work fabricated from cold-rolled and roll-formed light-gauge steel rather than hot-rolled sections. It is the engineering counterpart of AS 4100 (which covers hot-rolled steel), and the two are NOT interchangeable. A “steel-framed house” in Australia is almost always designed under AS/NZS 4600, not AS 4100 (verified 2026-05-16).

The brands a builder typically meets on a cold-formed steel residential job (BlueScope TrueCore, Stramit, Steeline, Bondor, Ranbuild) work to AS/NZS 4600 in-house. Their pre-cut frame, truss or purlin design submission is the AS/NZS 4600 output the builder reads.

Hot-rolled vs cold-formed in residential terms:

  • Hot-rolled (AS 4100): thick steel sections rolled at high temperature: UB lintels, UC columns, RHS goalpost portals. Used for heavy spanning and structural columns.
  • Cold-formed (AS/NZS 4600): thin-gauge steel formed at room temperature by roll-forming or press-braking: stud sections (C-section), top and bottom plates, roof battens, purlins, light-gauge truss chord and web members.

The two operate at different scales (thickness, tonnage, span) and have different design rules.

What it requires

For the cold-formed steel designer:

  1. Member sizing under cold-formed-specific rules. Local buckling, distortional buckling, and lateral-torsional buckling all behave differently in thin-gauge steel; AS/NZS 4600 provides the calculation methods.
  2. Effective section properties. Cold-formed sections have effective widths that change with stress level; the calculation reflects this.
  3. Connection design. Self-drilling screws, blind rivets, clinched joints, and welded joints in thin material are covered. Connection capacity is the most common failure path in cold-formed framing.
  4. Galvanised coating mass per AS/NZS 1397. The steel grade and coating mass affect design durability and corrosion allowance.
  5. Wind classification and load combinations. Per AS/NZS 1170.2 and AS 4055 for residential. The frame’s bracing and tie-down design flows from this.
  6. Manufacturer’s certification. Pre-cut residential frame kits arrive with a design certificate stating compliance with AS/NZS 4600 and naming the wind classification, span and loading.

What it doesn’t cover

  • Hot-rolled steel design. Lintels, columns, portals from hot-rolled sections sit under AS 4100.
  • Hot-rolled structural sections from mills. Section sizes are AS/NZS 3679; cold-formed feedstock is typically zincalume or galvanised coil to AS/NZS 1397.
  • Timber frame design. AS 1684 (residential), AS 1720 series (engineered timber).
  • Fabrication and erection rules. AS/NZS 5131 covers structural steelwork fabrication and is primarily aimed at hot-rolled construction; cold-formed pre-cut frames follow the manufacturer’s install manual rather than AS/NZS 5131.

Practical implications

  • Substituting hot-rolled for cold-formed in residential is a redesign. A drawing calling “100 PFC” (hot-rolled channel) cannot be substituted with a 100 cold-formed C-section even if dimensions match: section properties, connection capacity, and corrosion behaviour all differ.
  • Cold-formed steel frames need their own bracing detail. Strap bracing within the frame, fly bracing on trusses, longitudinal bracing on roof battens are all part of the AS/NZS 4600 design. Removing or omitting frame straps on site is a structural defect.
  • Field-modification of cold-formed members is more constrained than timber. Cutting, notching, or drilling a cold-formed stud member changes its effective section properties materially; the engineer’s design assumes the member is intact.
  • Corrosion management is the long-term issue. Cold-formed framing in marine or contact-with-water conditions needs higher coating mass and detail allowances per AS/NZS 4600 durability provisions. Standard residential framing uses Z275 or AM150 coating; coastal or wet conditions may need Z350 or higher.
  • Termite barriers still apply. Steel framing does not need anti-termite treatment, but the floor structure and the joinery above usually do. AS 3660.1 termite barrier requirements apply regardless of the frame material.

References

See also

Last updated: 2026-05-16. Verified: 2026-05-16. Quarterly review for currency.

Related articles