AS 1684.2:2021 – Residential Timber-Framed Construction: Non-Cyclonic Areas Guide

Standards Australia · Published 2021 · Active

Timber-framed buildings in residential zones must abide by strict design and construction requirements. These are set out in Australia’s primary framework, known as the AS 1684.2:2021 Standard. It provides prescriptive requirements for timber-framed residential homes located in non-cyclonic areas. The Standard is referenced in the National Construction Code as a Deemed-to-Satisfy solution, allowing builders and designers to achieve compliance without complex engineering for typical housing.

In the Standard, you will find span tables, fixing details, bracing systems, and tie-down specifications for walls, floors, and roofs. It provides a practical and efficient framework for consistent timber constructions across Australia. Following these requirements will guarantee your timber-framed buildings meet structural safety, stability, and resistance to wind loads. Are you building a timber structure within a bushfire-prone area? Assure to follow specific instructions to keep your building fire-resistant.

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📖 What Is AS 1684.2:2021?

✦ KEY TAKEAWAYS

• ✓ Sets design and construction rules for residential timber framing.
• ✓ Designed for non-cyclonic wind classifications N1 to N4.
• ✓ Cyclone-prone areas must use AS 1684.3 instead.

The AS 1684.2:2021 Standard, titled ‘Residential Timber-Framed Construction - Part 2: Non-Cyclonic Areas’, sets the design and construction requirements for standard residential timber-framed buildings in non-cyclonic areas such as houses, townhouses, and low-rise residential properties. It is the Australian Standard that provides span tables and structural requirements for timber members used in house framing, including floor, wall, roof, tie-down systems, and connections. It promotes better material usage, improved safety, cost efficiency, structural integrity, and homeowner confidence.

This is part 2 of the AS 1684 series and is specifically designed for non-cyclonic wind classifications N1 to N4. Most southern regions of Australia fall under this Standard, while northern cyclone-prone areas must use the AS 1684.3 Standard.

📖 Scope and Application

✦ KEY TAKEAWAYS

• ✓ Deemed-to-Satisfy solution under the National Construction Code.
• ✓ Applies to Class 1 and Class 10 buildings in non-cyclonic areas.
• ✓ Covers wall, floor, roof framing, connections and tie-down details.

The AS 1684.2 framework provides prescriptive design and construction requirements for timber-framed buildings in non-cyclonic areas. It is referenced by the National Construction Code (NCC) as the Deemed-to-Satisfy solution for residential timber framing. In other words, timber framing structures built according to the Standard are automatically compliant with NCC requirements.

The Standard applies to Class 1 (houses, townhouses, and villas) and Class 10 (non-habitable structures such as carports, garages, and sheds) buildings in non-cyclonic areas. It includes design rules, span tables, and construction details for timber wall framing, floor systems, roof framing, and associated connections and tie-down.

📖 Timber Member Requirements

✦ KEY TAKEAWAYS

• ✓ Standard stud sizes 70x35mm or 90x35mm; spacing 450mm or 600mm.
• ✓ Joists and rafters typically spaced at 450mm or 600mm centres.
• ✓ Sizes selected from span tables based on load and span conditions.

The AS 1684 Standard sets out rules for selection, sizing, spacing, and installation of timber members used in wall frames, floor systems, roof framing, and structural connections.

Wall Framing Members

The requirements for wall framing members include studs, noggings, plates, and lintels.

Studs must be placed vertical, continuous, and adequately restrained via noggings. The sizes are selected from span tables based on wall height and roof and floor load, typically 70x35mm or 90x35mm. Stud spacing is generally 450mm or 600mm.

Top plates are required to tie walls together and distribute loads from the roof. Usually, double top plates are required. Bottom plates transfer the load to the structure below and should be fixed to the floor or subfloor.

Noggings provide lateral restraint to studs. At least one row of noggings is required for standard wall heights.

Lintels support loads over windows and doors. The size is selected from span tables based on opening width and load. Larger openings require deeper or multiple-member lintels.

Floor Systems

The requirements for floor systems include bearers, joists and flooring specifications.

Bearers support joists and transfer loads to posts or stumps. The size is determined from the span tables based on load width, and span between supports.

Joists support the flooring loads and are typically spaced 450mm or 600mm. The size is selected from the span tables depending on span length and load type.

Flooring can be timber or sheet flooring (eg particleboard). It must be properly fixed to the joists and provide diaphragm action. The thickness depends on joist spacing.

Roof Framing

Roof framing requirements cover rafters, ridges, collar ties, ceiling joists, and purlins.

Rafters support roof loads and are generally spaced 450mm or 600mm. The size depends on roof pitch, span, and load.

Ridges provide fixing points for the rafters and are usually not load-bearing. If ridge beams are required, their sizing will be determined from the span tables.

Collar ties prevent rafters from separating and must be installed in the upper third part of the roof space.

The size and spacing requirements for ceiling joists and purlins depend upon the span tables. Ceiling joists are typically aligned with the rafter spacing.

📖 How to Use the Span Tables

✦ KEY TAKEAWAYS

• ✓ Four key inputs: wind class, site conditions, spacing and span.
• ✓ Higher wind class requires stronger or larger timber.
• ✓ Builders often design backwards from span tables.

Span tables provide maximum allowable spans for each timber member type based on timber species, grade, and load conditions. Before opening a span table, you need these four key inputs: wind classification, site conditions, spacing of members, and span. The wind classification is based on wind speed, terrain, and shielding. A higher wind class requires stronger or larger timber. Site conditions look at exposure and topography, affecting wind classification and load. The spacing determines the distance between members which is usually 450mm or 600mm. Wider spacing needs larger timber. Span decides the distance between supports and can be a single span (simple support) or continuous span (over multiple supports).

How to read an AS 1684 span table?

Builders often design backwards from span tables. They will choose a spacing, check the spans, and then select the timber.

📖 Connection and Fastener Requirements

✦ KEY TAKEAWAYS

• ✓ Common bolt sizes M10, M12, or M16 with required washers.
• ✓ Complete tie-down chain required from roof to footing.
• ✓ Bracing resists lateral wind forces on walls and roofs.

The AS 1684.2 Standard specifies minimum nail, bolt, and connector requirements for all timber member connections.

Nails, Bolts and Connectors

Nails are the most common fixing method that must comply with the specified diameter and lengths, and the required number of nails per joint. Bolts are used where higher loads occur. They are typically hex-head or cup-head with the most common sizes being M10, M12, or M16. For seasoned timber, bolt holes should be no more than 1mm larger than the bolt diameter. Washers are necessary to prevent the bolt from pulling through the timber, and must be installed against the timber face. Connectors include strap ties, framing anchors, and joist hangers, and are used when nail-only fixing is insufficient or loads are high.

Tie-Down Chain

To resist wind uplift and racking forces, AS 1684 requires a complete tie-down chain. Every connection must transfer load down to the ground. The key tie-down points include roof to wall, wall to floor, and floor to footing. Trusses should be tied to the top plates using straps, connectors, or nails depending on the load. Studs have to be connected to the bottom plates and floor framing, while bearers should be tied to stumps or slab.

Bracing Requirements

Bracing requirements are necessary to resist lateral forces caused by wind. Wall bracing can include sheet bracing like plywood and fibre cement, or diagonal bracing such as steel or timber. Wall bracing must provide sufficient bracing units based on wind classification and building size. Strict nailing patterns are required, and edge and spacing rules are critical.

Roof and ceiling bracing includes ceiling diaphragm, diagonal bracing straps, and purlin bracing. This stabilises the roof structure and transfers the load to braced walls.

📖 Closing Remarks

Architects, designers, builders, and contractors involved in designing and constructing timber-framed structures must assure buildings are safe and comply with local building code regulations. Our AS 1684.2:2021 Standard offers guidance on the minimum requirements for standard residential timber-framed buildings that are located in non-cyclonic areas. It provides information about timber members, span tables, and connection and fastener specifications. Purchase your PDF or hardcopy today and construct buildings that comply with the regulations.