AS 1684 Residential Timber-Framed Construction Explained
AS 1684 is the Australian Standard for timber-framed residential construction, covering the design, installation, and construction of timber structures for housing and low-rise buildings. It's a vital reference for builders, engineers, inspectors, and anyone involved in residential timber construction.
This guide breaks down the entire AS 1684 series into understandable parts and highlights the key requirements that relate to inspections, compliance, and construction practices.
What is AS 1684?
AS 1684 is the national standard for timber-framed construction in Australia. It provides engineering and building guidance for:
Timber member sizing (e.g., joists, studs, rafters)
Wind load compliance
Bracing and tie-downs
Frame layout and construction tolerances
It ensures that residential timber buildings are designed and constructed safely, efficiently, and cost-effectively.
The Four Parts of AS 1684
Part 1 outlines the design criteria used to develop span tables and structural performance requirements. This part is primarily used by engineers and designers to inform calculations and custom structural designs.
Part 2 focuses on non-cyclonic areas and provides detailed construction practices for regions with low to moderate wind classifications (up to N4). It is applicable across most of Australia and is widely used in standard residential projects.
Part 3 is designed for cyclonic regions, particularly those in northern coastal areas like Queensland and parts of the Northern Territory. It contains specific provisions for wind loads in areas prone to cyclones.
Part 4 offers a simplified version of Part 2 for non-cyclonic conditions (N1 and N2 wind zones only). It is more user-friendly and popular among builders and contractors for standard timber-framed residential homes, particularly where engineering support is minimal or not required.
Cyclonic vs Non-Cyclonic
Part 2 and 4 apply to non-cyclonic areas (e.g., Perth, Adelaide, Melbourne).
Part 3 applies to cyclonic zones (e.g., Cairns, Darwin).
Each part adjusts structural requirements like bracing, connections, and tie-downs based on wind classification zones from N1 to N4 and C1 to C4.
Key Design Criteria
Both Part 2 and Part 4 are intended for:
Single or double-storey homes
Roof pitches up to 30° (Part 4) or 35° (Part 2)
External wall height up to 2.7 m (Part 4) or 3.0 m (Part 2)
Building width up to 12 m (Part 4) or 16 m (Part 2)
Span Tables and Structural Performance
Part 2: Includes CD-based span tables; more flexible but needs more input.
Part 4: Has printed span tables with fewer options and higher safety margins.
Part 4 tends to over-engineer, leading to larger timber sizes and higher costs, while Part 2 allows for economical design choices through calculated results.
Bracing Requirements
Part 4 uses a simple 4-step system with bracing types A & B.
Part 2 involves detailed bracing calculations in kN/m.
Bracing requirements protect structures from lateral wind forces and prevent frame racking or collapse.
Connections and Fasteners
AS 1684 outlines:
Nailing patterns
Tie-down locations
Fixings for top/bottom plates, trusses, and studs
These connection requirements vary between wind classifications and are essential for frame integrity and safety.
Limitations of the Simplified Version (Part 4)
While easier to use, Part 4:
Is restricted to N1 and N2 wind zones
Limits building size and height
Offers fewer bracing/connection options
Can be less cost-effective due to over-sizing
Use Part 4 for quick builds, but Part 2 is better for custom or budget-conscious projects.
Why AS 1684 Matters in Building Inspections
As inspectors, we reference AS 1684 when:
Assessing framing quality
Verifying compliance with bracing and fixing
Checking sizing of joists, studs, and rafters
Reviewing modifications or renovations
If your builder deviates from AS 1684 without an engineer’s sign-off, compliance issues may arise during inspection or certification.
Book an Inspection in Perth
Our inspectors are fully trained to assess timber-framed homes against AS 1684. Whether you’re building, buying, or renovating — book an inspection today to ensure your structure is safe, compliant, and built to last.
FAQ
Q: Is AS 1684 mandatory?
Yes, it’s referenced in the National Construction Code (NCC) for timber framing compliance.
Q: Can I use AS 1684 for steel frames?
No, AS 1684 only applies to timber-framed buildings.
Q: Do I need an engineer if I follow AS 1684?
Not always. Part 4 is designed for non-engineered builds. But for anything outside the standard’s limits, you’ll need an engineer’s design.
Q: Is Part 4 good enough for a typical house?
Yes, if your project is in N1 or N2 wind zones and within size limits. Otherwise, use Part 2.
Q: Can AS 1684 be used for double-storey homes?
Yes, AS 1684 applies to single and double-storey conventional timber-framed buildings. However, the design limitations—such as maximum wall height and span—must still be followed unless an engineer certifies an alternative.
Q: What wind classifications are covered in AS 1684?
AS 1684 covers wind classifications from N1 to N4 (non-cyclonic) in Parts 2 and 4, and C1 to C4 (cyclonic) in Part 3. Your builder must determine your wind zone based on geographic location and site conditions.
Q: Is AS 1684 suitable for renovations or extensions?
Yes, AS 1684 can be used as a guide for timber-framed extensions and alterations, provided the work falls within the scope of the standard and the original structure is compatible.
Q: Do all frame members need to follow AS 1684 span tables?
Yes, unless an engineer provides alternative calculations, all structural members such as studs, bearers, joists, and rafters must comply with the span tables and installation rules defined in AS 1684.
Q: How does AS 1684 interact with other standards like AS 1720 or AS 2870?
AS 1684 is used for general timber framing. AS 1720 focuses on timber engineering design, while AS 2870 covers slabs and footings. All three may be referenced together in complex builds for full structural compliance.