Steel Frame Construction Requirements for Class 1 Buildings

What This Requirement Covers

This requirement sets out how steel framing and structural steel must be designed, constructed and detailed for single dwellings and other Class 1 buildings under the National Construction Code (NCC) in Australia. It explains which design standards and Deemed-to-Satisfy (DtS) provisions can be used, the limitations that apply to low-rise residential steel framing, and the relationship between the ABCB Housing Provisions (NCC Volume Two), NCC Volume One references for steel structures, and applicable Australian Standards. It exists to ensure structural safety, durability and fitness-for-purpose for residential steel framed buildings while offering a workable DtS path for common low-rise house forms.

This requirement primarily applies to designers, builders and certifiers working on Class 1a (single houses, townhouses) and Class 1b (boarding houses/guest houses within scope) and associated Class 10 structures. It also identifies when higher-level standards for steel structures (used more commonly in Class 2-9 buildings) are required instead of the residential DtS options.

Key Requirements

1. Applicable building class:
2. Class 1 and Class 10 buildings are covered by NCC Volume Two - ABCB Housing Provisions (see H1D6 and Part 6.3 where relevant). For other building classes, NCC Volume One references apply.
3. Acceptable design standards for steel framing (DtS solutions):
4. Residential and low-rise steel framing may be designed to the NASH Standard - Residential and Low-Rise Steel Framing (Part 1 for design; Part 2 for design solutions) as referenced in NCC Volume Two (H1D6).
5. For general steel structures, use AS 4100 - Steel Structures (NCC Volume One reference). For cold-formed steel structures, use AS/NZS 4600 - Cold-formed steel structures (NCC Volume One reference).
6. When NCC Volume Two allows Part 6.3 of the ABCB Housing Provisions (sample DtS steel design), conditions include (H1D6(5)-(6)):
7. Building located in wind class N3 or lower (refer AS 4055 for geographic limits).
8. First dimension of steel sections must be installed vertically.
9. All loads must be evenly distributed (unless noted otherwise).
10. Building is not subject to snow loads and Appendix A of AS 1170.4 contains no specific earthquake design requirements for the site.
11. Structural members must be within geometric limits in clause 1.2 of AS 4055 (see specific limits in that standard).
12. Software and geometric limits for computer-aided DtS design (H1D6(7)):
13. Structural software that implements DtS criteria must comply with the ABCB Protocol for Structural Software. When so used, buildings must be within these geometric limits:
14. Eaves height (ground to underside of eaves): not more than 6.0 m.
15. Overall height (ground to highest roof point): not more than 8.5 m.
16. Building width (including roofed verandahs, excluding eaves): not more than 16.0 m.
17. Building length: not more than 5 times the building width.
18. Roof pitch: not more than 35 degrees.
19. Corrosion protection and durability:
20. Corrosion protection for structural steel must follow AS 4100 or, where the ABCB Housing Provisions are used for corrosion protection, clause 6.3.9 of Part 6.3 (NCC Volume Two) (see H1D6(5)(d)). Exact coating types, galvanizing thicknesses and exposure classifications must follow the referenced standards and project specification.
21. Structural design for strength and deflection:
22. Where AS 4100 or AS/NZS 4600 are not used, Part 6.3 of the ABCB Housing Provisions may be used for structural stability, strength and deflection subject to the conditions above (H1D6(5)(c)-(6)).
23. Referenced Standards and NCC clauses (examples):
24. NCC Volume Two - ABCB Housing Provisions: H1D6 Framing, Part 6.3 (structural steel provisions), and H1D5 for related design requirements.
25. NCC Volume One: steel construction references under Structure (AS 4100, AS/NZS 4600) and composite references (AS/NZS 2327) where applicable.
26. Australian Standards: AS 4100, AS/NZS 4600, NASH Standard - Residential and Low-Rise Steel Framing (Part 1 & Part 2), AS 1170.2/1170.4 (wind and earthquake loading), AS 4055 (wind classification and geometric limits for residential buildings), AS 1684 (timber framing rules where hybrid framing applies), AS 3700 if masonry interface occurs.

Residential vs Commercial

1. Residential (Class 1 and 10):
2. DtS paths exist specifically for residential and low-rise steel framing using the NASH Standard - Residential and Low-Rise Steel Framing and the ABCB Housing Provisions (Part 6.3) when the specified limitations are met (wind class N3 or lower, geometric limits, no snow loads, etc.). These DtS options simplify design for typical houses and domestic outbuildings.
3. Use of structural software implementing DtS rules is permitted within stated geometric limits (eaves height ≤ 6.0 m, overall height ≤ 8.5 m, width ≤ 16.0 m, roof pitch ≤ 35°).
4. Commercial / higher classes (Class 2-9):
5. Must follow NCC Volume One structural provisions. Typical design standards are AS 4100 for steel structures and AS/NZS 4600 for cold-formed steel. There is no reliance on the residential NASH DtS provisions for larger or non-residential buildings. More conservative fire resistance, load case and durability rules apply.

Exceptions and Exemptions

1. Use of Part 6.3 DtS provisions is conditional. Exemptions to using the residential DtS route occur when:
2. Building is in wind class above N3.
3. Site is in an alpine area or where AS 1170.4 imposes seismic requirements (Appendix A contains earthquake design requirements).
4. Structural sections are oriented with their first dimension horizontal (the DtS Part 6.3 condition requires vertical installation of the first dimension).
5. Building is subject to snow loads.
6. Structural designers may instead provide a performance solution designed to AS 4100 or AS/NZS 4600 when the DtS conditions are not satisfied.
7. Alternative solutions:
8. Where DtS is not appropriate, a performance solution prepared by a suitably qualified engineer using AS 4100 (or AS/NZS 4600 for cold-formed members) is acceptable under the NCC.

State and Territory Variations

1. The NCC is national but each state and territory can adopt schedules or variations. Designers must check the state schedules in NCC Volume One (Schedules 4-12) for local amendments that could affect steel framing requirements. Examples to consider:
2. Queensland: the NCC Housing Provisions include specific references and may apply additional limitations for cyclonic regions (see H1D6(4) for timber - equivalent attention needed for steel in high wind/cyclonic areas). Cyclonic areas require cyclone-specific design and may invalidate Part 6.3 DtS use.
3. New South Wales, Victoria, Western Australia, South Australia, Tasmania, Northern Territory and ACT: verify each jurisdiction schedule for any modifications to wind classifications, corrosion requirements or references to AS standards.
4. Always confirm local council or state building regulator requirements where additional corrosion protection, tie-down, or bracing specifications apply (for example in coastal or high-corrosion zones).

Practical Compliance Tips

1. Check the wind classification first. Confirm the site wind class (AS 4055 / AS 1170.2) before choosing the NASH DtS route - if wind class is above N3, plan a structural engineer solution using AS 4100 or AS/NZS 4600.
2. Verify geometric limits early. If the design exceeds eaves 6.0 m, overall height 8.5 m, width 16.0 m or roof pitch 35°, do not rely on DtS software tables; engage an engineer.
3. Use the correct standard for the steel type. For cold-formed members use AS/NZS 4600; for hot-rolled structural sections use AS 4100; for residential low-rise consider the NASH Standard only when DtS conditions are met.
4. Document corrosion protection. Specify coatings, galvanizing thickness and exposure classification in the contract documents in accordance with AS 4100 and clause 6.3.9 of the ABCB Housing Provisions when applicable.
5. Keep structural software compliant. If using software for DtS design, ensure it meets the ABCB Protocol for Structural Software and that input geometry stays within the stated limits.
6. Detail connections and load paths. Common defects arise from undersized connections and omitted bracing - specify connection sizes, fastener types and bracing systems conforming to the referenced standards and NASH detail schedules.
7. Check state schedules and local requirements. Before finalising design or construction, review the NCC state schedule for the project state or territory and consult the local certifier for any additional requirements (especially in coastal, cyclonic or high-seismic risk areas).

References (examples of code citations used above)

1. NCC 2022 Volume Two - ABCB Housing Provisions, H1D6 Framing; Part 6.3 structural steel provisions.
2. NCC 2022 Volume One - Structure references to AS 4100, AS/NZS 4600 and NASH Standard.
3. AS 4100 - Steel Structures.
4. AS/NZS 4600 - Cold-formed steel structures.
5. NASH Standard - Residential and Low-Rise Steel Framing (Part 1 and Part 2).
6. AS 1170.2 and AS 1170.4 - Wind and earthquake actions (as referenced).
7. AS 4055 - Wind classifications and geometric limits for residential buildings.

Note: This article summarises the Deemed-to-Satisfy paths and key constraints for steel framing in Class 1 buildings under the NCC. Always refer to the exact clauses identified above in the current NCC edition and the full text of the referenced Australian Standards for design and construction details. If requirements are unclear for your specific project, engage a registered structural engineer or building certifier and check any state schedule amendments in NCC Volume One.