AS 1684: residential timber-framed construction

TL;DR

AS 1684 is the four-part Australian Standard for residential timber-framed construction. Following it is the primary deemed-to-satisfy (DTS) path for satisfying NCC 2022 Vol 2 performance requirement H1P1 (structure) on Class 1 and Class 10 buildings. Parts 2 and 3 (the 2021 editions) are the working tools: Part 2 covers non-cyclonic areas (wind classes N1-N4), Part 3 covers cyclonic areas (C1-C3). For N5, N6, or C4 sites, the standard doesn’t reach and the frame needs engineer design. The span tables are published as separate supplements, not in the body of the standard. The critical framing failure mode is wind class mismatch: building to N2 on a site that’s been classified N4 means undersized tie-downs and bracing, which shows up as structural failure in a storm.

In plain English

AS 1684 tells chippies and builders what timber to use, how to size it, how to connect it, and how to brace it in a residential timber-framed house. It translates the structural performance requirements of the NCC into prescriptive rules that can be followed on site without engaging a structural engineer for every frame. Where a designer uses span tables from AS 1684.2, the result is DTS-compliant framing provided the inputs (timber species, stress grade, wind classification, roof loads) are correct.

The series has four parts with different purposes and currency:

Part	Title	Current edition	Coverage
AS 1684.1	Design criteria	1999, Amd 1:2002	Engineering basis for span tables in Parts 2-4; used by engineers and product manufacturers
AS 1684.2	Non-cyclonic areas	2021, Amd 1:2024	Standard DTS path for most Australian residential builds (wind classes N1-N4)
AS 1684.3	Cyclonic areas	2021	DTS path for cyclone-prone areas (wind classes C1-C3)
AS 1684.4	Simplified, non-cyclonic	2024	Simplified DTS path for N1/N2 areas; more limited scope geometry

AS 1684.2:2021 superseded AS 1684.2-2010 and is the version referenced by NCC 2022 under H1D6(4) (verified 2026-05-08, Standards Australia NCC 2022 spotlight).

What it requires

Wind classification: the first input

Before a single piece of timber is specified, the site must have a wind classification under AS 4055:2021. The classification determines which span tables and connection details apply to the frame. Getting the classification wrong is the most consequential framing error on a residential site.

Wind class	Gust speed (ULS, m/s)	Where typically found	AS 1684 coverage
N1	34	Sheltered, low terrain	AS 1684.2 and AS 1684.4
N2	40	Standard suburban, shielded	AS 1684.2 and AS 1684.4
N3	50	Exposed coastal, hilly terrain	AS 1684.2
N4	61	High exposure, open ridgelines	AS 1684.2
N5	74	Extreme exposure	Outside AS 1684 scope; engineer design required
N6	86	Extreme exposure	Outside AS 1684 scope; engineer design required
C1	50	Low cyclone risk, QLD/WA north	AS 1684.3
C2	61	Moderate cyclone zones	AS 1684.3
C3	74	High cyclone zones	AS 1684.3
C4	86	Severe cyclone zones	Outside AS 1684 scope; engineer design required

Wind speeds sourced from AS 4055:2021 (verified 2026-05-08, Excelo Consulting Engineers AS 4055 guide). The wind classification is determined by the site’s wind region (AS/NZS 1170.2), terrain category, topography, and shielding. It must be established and documented before the frame design proceeds.

Span tables

The span tables are the practical output of AS 1684. They tell the chippy or builder what size timber to use for a given span, spacing, load, and timber stress grade. Tables are published as separate supplements to AS 1684.2 and AS 1684.3, not within the main standard body. Separate supplement booklets exist for different combinations of wind classification, timber species group, and stress grade (e.g. N1/N2 seasoned softwood MGP10, N3 seasoned softwood F8, N4 hardwood F17, and so on).

The tables cover the main framing members:

Rafters (roof slope members carrying the roofing load)
Roof battens (purlins carrying roofing sheets or tiles to rafters)
Ceiling joists (ceiling-level horizontal members, carrying ceiling load)
Underpurlins (mid-span support for rafters)
Ridge boards and hips
Floor joists (spanning between bearers, carrying floor load)
Bearers (supporting floor joists, spanning between stumps or posts)
Lintels (spanning over openings in walls)
Studs (vertical wall members; size depends on height, load, wind class)
Top and bottom plates

Reading span tables requires correct inputs: the timber’s seasoned or unseasoned status, its species group or stress grade, the member spacing, the load width or roof area supported, and the wind class. An incorrect input in any one of these produces an undersized member.

Bracing

AS 1684 provides bracing systems for both in-plane wall racking (resistance to lateral wind load) and diaphragm action of floors and roofs. The required bracing capacity is derived from the wind classification, building geometry (footprint, roof type, wall height), and the location of openings in walls.

Bracing can be provided by:

Structural plywood or particleboard sheet bracing
Cross-diagonal metal strap bracing
Proprietary bracing products (system-approved; engineering data supplied by manufacturer)
Concrete or masonry walls used as structural bracing elements

The design of the bracing layout is often done on a bracing plan that goes to the building surveyor (certifier) as part of the permit documentation.

Tie-downs

The connection path from roof members down to the foundation must resist wind uplift at every joint. AS 1684 specifies the uplift forces at each connection for each wind class and building geometry, and provides a range of acceptable connector types (triple grips, framing anchors, rods, proprietary hold-downs). The higher the wind classification, the larger the uplift forces and the heavier the connectors required.

The tie-down chain runs from roof battens to rafters, rafters to top plate, studs to bottom plate, bottom plate to foundation (slab edge bolt, stump bolts, or screw piles). Missing or undersized connectors anywhere in the chain is a defect. This is a mandatory inspection item at the framing stage.

Timber species and stress grades

AS 1684 uses a stress grade system (MGP10, MGP12, MGP15 for pine; F-grades for hardwood; LVL products have manufacturer-certified values) to classify timber by structural capacity. The span tables are keyed to stress grade, not timber species. The species must be verified to meet the stated stress grade via a grading certificate or the supplier’s species listing.

AS 1684.2:2021 introduced changes to floor framing details and updated provisions for metal roof battens and masonry tie-down straps, reflecting more than a decade of research since the 2010 edition (verified 2026-05-08, Standards Australia blog).

Timber workmanship tolerances under AS 1684

AS 1684 sets dimensional requirements for framing members. Workmanship tolerances for finished frames (wall plumb, straightness, twist in individual members) are covered in the HIA Guide to Materials and Workmanship. The verified numerical tolerances are pending HIA member access: [HIA-033].

What it doesn’t cover

AS 1684 applies to timber-framed Class 1 and Class 10 buildings only. Exclusions:

Steel framing: covered by AS/NZS 4600 (cold-formed) and referenced separately under NCC H1D6(3)
Engineered timber products (LVL, Glulam, CLT): span tables in AS 1684 do not cover LVL and similar; use manufacturer’s certified span tables or engineer design
Wind classes N5, N6, C4: beyond the standard’s scope, engineer design required
Multi-storey framing beyond the geometric limits of the standard
Commercial buildings (Class 2-9 under NCC Volume One)
Truss design: nail-plated trusses use AS 1720.5; the truss manufacturer provides certified engineering. AS 1684 does not design the truss, only specifies how the truss is connected to the frame.

Practical implications

NCC compliance pathway

The compliance pathway for a timber-framed residential build:

Site wind classification determined under AS 4055:2021
Frame designed using AS 1684.2 (non-cyclonic) or AS 1684.3 (cyclonic) span tables for the confirmed wind class and timber grades
Bracing layout drawn up and documented
Tie-down schedule prepared per AS 1684 uplift tables
Framing inspected at frame stage by the building surveyor or certifier
Any deviation from span table selections or connection schedules must be covered by engineer’s details

NCC 2022 Vol 2, H1D6(4) makes AS 1684.2 and AS 1684.3 the DTS solution for timber framing performance requirement H1P1 (verified 2026-05-08, NCC 2022 Vol 2 Part H1).

Queensland variation

Queensland replaces H1D6(4) in NCC 2022 and removes AS 1684.4 as an option. QLD residential timber frames must use AS 1684.2 (non-cyclonic) or AS 1684.3 (cyclonic); the simplified Part 4 is not an acceptable DTS path in QLD (verified 2026-05-08, NCC 2022 Vol 2 Part H1).

AS 1684.4: when to use it

AS 1684.4:2024 is the simplified path for N1/N2 sites. It covers a more limited range of house geometry and timber grades than Part 2. Use it where the project fits within its scope and the N1/N2 wind class is confirmed. Part 4 underwent a major revision in 2024 to align with the bracing and tie-down changes made in Part 2:2021, particularly the transition from JD4 to JD5 joint groups (verified 2026-05-08, Standards AU AS 1684.4-2024). Do not use the superseded 2010 edition of Part 4 on new projects.

Common framing defects at frame inspection

Defect	Cause
Wrong wind class applied	Site classification not obtained before frame design; builder assumes N2 on a coastal N3+ site
Undersized members	Span tables read with wrong stress grade or wrong load width
Missing or wrong tie-downs	Tie-down schedule not prepared; generic triple-grips used where heavier connectors required
Bracing wall in wrong location	Bracing plan not prepared; openings cut after bracing installed
LVL beam selected from AS 1684 table	AS 1684 span tables do not apply to LVL; must use manufacturer’s certified tables
Engineered timber noggings omitted	AS 1684.2 nogging requirements missed for sheet-edge fixing or restraint
Superseded edition used	Part 4-2010 used instead of Part 4-2024 on new project

Source link

Standards Australia: AS 1684.2:2021 product page (verified 2026-05-08). The standard is paywalled. The NCC 2022 Volume Two Part H1, which sets out the DTS pathway referencing AS 1684, is free at ncc.abcb.gov.au.

References

Standards Australia, AS 1684.2:2021 Amd 1:2024, Residential timber-framed construction, Part 2: Non-cyclonic areas. https://store.standards.org.au/product/as-1684-2-2021-amd-1-2024 (verified 2026-05-08).
Standards Australia, AS 1684.3:2021, Residential timber-framed construction, Part 3: Cyclonic areas. https://store.standards.org.au/product/as-1684-3-2021 (verified 2026-05-08).
Australian Building Codes Board, NCC 2022 Volume Two, Part H1 Structure. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-two/h-class-1-and-10-buildings/part-h1-structure (verified 2026-05-08).
Standards Australia, NCC 2022 Standards Spotlight: Residential Timber-Framed Construction. https://www.standards.org.au/blog/ncc-2022-standards-spotlight-residential-timber-framed-construction (verified 2026-05-08).
WoodSolutions, AS 1684 Code Compliance. https://www.woodsolutions.com.au/resources/standards-codes/as1684-code-compliance (verified 2026-05-08).
Excelo Consulting Engineers, Wind Classification to AS 4055 Calculator. https://exceloce.com.au/calculators/wind-classification-to-as-4055-calculator/ (verified 2026-05-08).

NCC 2022 Volume Two, the residential building code that calls up AS 1684 under H1D6(4)
ABCB Housing Provisions, the DTS manual that sits alongside NCC Vol 2 for residential construction
NCC structure (BCA/PCA), how the NCC is structured and how performance requirements work
Noggings, short horizontal blocking members in timber walls, governed by AS 1684 spacing and fixing rules
Tie-down, the connection chain from roof to foundation resisting wind uplift as required by AS 1684
Deemed-to-satisfy, how following AS 1684 satisfies NCC performance requirements without a performance solution