Meeting the structural requirements for stair and barrier design

This web page provides an overview of information required for the design, documentation and construction of stairs and barriers, including in accordance with AS/NZS 1170.1 Structural design actions, Part 1: Permanent, imposed and other actions, and highlights the responsibilities of the contributing parties.

Building practitioners are required to ensure compliance is properly documented for H5P1 and H5P2 of the National Construction Code (NCC) Volume Two 2022 for Class 1 and 10 buildings in building permit documentation, where the design includes stairs and barriers.

Compliance with the performance requirements B1P1 and B1P2 of NCC Volume 1 of NCC Volume 1 should also be met for stairs and barriers in Class 2-9 buildings.

It has been identified through our Building Documentation Audit Program, and similar audits in other states, that these requirements are not being documented or inadequately documented in the approved design.

Under section 24 of the Building Act 1993 (the Act), relevant building surveyors (RBS) are obliged to not issue a building permit unless they are satisfied that the building work and the building permit will comply with the Act and the building regulations, including the NCC.

Accordingly, the RBS, prior to issuing a building permit, should ensure the design of stairways and barriers meets the performance requirements. This includes satisfying AS/NZS 1170.1 for compliance when a deemed-to-satisfy (DtS) solution is the proposed method of complying with the performance requirements.

NCC compliance requirements

For Class 1 and 10 buildings performance requirements ‘H5P1 Movement to and within a building’ (formerly P2.5.1) and ‘H5P2 Fall prevention barriers’ (formerly P2.5.2) set out requirements so that people can move safely to and within a building and have barriers, where people could fall one metre or more.

Where performance requirements H5P1 and H5P2 in NCC 2022 are satisfied using a DtS solution, ‘H5D2 Stairway and ramp construction’ and ‘H5D3 Barriers and handrails’ require compliance with housing provisions parts 11.2 and 11.3.

Clause 11.2.2 ‘Stairway construction’ and Clause 11.3.4 'Construction of barriers to prevent falls’ requires stairways and certain barriers to be designed to take loading forces in accordance with AS/NZS 1170.1.

AS/NZS 1170.1 sets out the loading requirements for Stairs in ‘Clause 3.4 Floors and barriers’, including balustrades in ‘Clause 3.6 Barriers’. Applicants and design practitioners should ensure that when preparing design documentation for a building permit that these requirements are detailed in the design. This includes evidence of suitability in accordance with NCC clause A5G3 for the design of stairways and barriers in accordance with AS/NZS 1170.1.

Design information for stairs

General requirements

• External or internal stairs, landing and ramps shall be designed for loadings in accordance with AS/NZS 1170.1 including self-weight, weight of floor finishes and imposed actions as per Clause 3.4.
• For timber stairs, the designer shall design stringers and treads based on the stair width, imposed loadings and cater appropriately for exposure condition / durability and termite protection of timber stair. Connection design is of particular importance for timber and fixings should comply with spacing and edge clearance requirements of AS 1720.1 Timber structures, Part 1: Design methods.

Commercial (Class 2 to 9)

• Stairs and ramps within commercial buildings (type-B activity/occupancy) shall be designed for same imposed actions as the area providing access but not less than 4.0kPa uniformly distributed action and 1.8 kN concentrated load, as per Table 3.1 in AS/NZS 1170.1.
• Higher uniformly distributed and concentrated actions must be considered for the areas where people may congregate, shopping areas, warehouses and vehicle traffic areas (type-C, D and E activity/occupancy) as per Table 3.1 in AS/NZS 1170.1.

Design information for barriers

General requirements

• A barrier including top edge and infill must be designed to withstand imposed actions in accordance with AS/NZS 1170.1 Clause 3.6. All barriers must be designed as applicable for wind effects as per AS/NZS 1170.2 or structural robustness as per AS/NZS 1170.0.
• Barriers shall be designed and documented for critical load combinations for ultimate limit states as per Clause 4.2 AS 1170.0. Designer shall note that all loads are not additive and the critical load combination must be adopted and applied at most critical location.
• The design should comply with suggested serviceability limit state criteria as per Appendix C of AS 1170.0.
• All components of proprietary glazing system including post, top-bottom rails, internal chords, connection plate, bolts, cap plates etc. must be compliant to AS/NZS 1170.1 and adequately weatherproofed for external use. Site specific weatherproofing will ensure the barrier’s functionality for its lifespan.
• Glazed barriers and openable windows serving as a barrier must be designed for human impact. The selection and installation of a glazed barrier must be done in accordance with AS 1288.
• For interlinking handrails, where the glass balustrade panels are structural and support handrail loads, the handrail must be designed with the structural capacity suitable for fall prevention in the event that any of the one supporting glass panels has been broken. The design needs to confirm that the glass panels are designed to support the increased handrail loads spanning across a broken panel section. A design incorporating an interlinking handrail must also adhere to one of three options for the fixing/support of the handrail, as well as the specific glazing requirements as set out in AS 1288 Section 7.
• For timber barrier systems in above ground applications exposed to the weather, or where subjected to other sources of moisture/deterioration, handrails, posts, newels, balusters, and infills, should be either:
  • Above ground durability Class 1 species, such as blackbutt, spotted gum, ironbark, jarrah, merbau or kwila with any sapwood present treated to H3 (or higher).
  • H3 (or higher) treated softwood, such as slash, Aruacana (hoop) or radiata pine.
  • Preservative treatment shall comply with AS 1604.
  • Also consider termite protection for durability throughout the lifespan in regions susceptible to termite infestation as designated by the local Council.

Commercial (Class 2 to 9)

• Barriers in light and medium traffic areas (Type F/G occupancy as per Table 3.3 AS/NZS 1170.1) shall be designed for higher horizontal impact forces by vehicles as per AS/NZS 1170.1 Clause 3.8.
• Barriers in areas where people may congregate and subject to overcrowding will also require additional consideration for higher imposed loading, as noted in AS 1170.1 Clause 3.6 and Table 3.3.

Connection of barrier or balustrades to substrate

• Designer must design for the project specific substrate i.e. timber, concrete, steel. Barrier (post, handrail, balustrade) connections and fixings shall be documented for critical load combinations of actions for ultimate limit states.
• Designer must evaluate type of fixtures to be used based on project specific needs, substrate material and recommendation by manufacturer’s specification (specifier product guide). To ensure integrity and performance of fixtures, the designer must maintain minimum edge distance and spacing between the fixtures (applies to the barrier members as well as the substrate material).
• Designer shall also consider geometrical constraints of the adopted barrier system and must allow for sufficient edge beams/bearers to execute efficient connection detail and mitigate twisting in barrier.
• Internal barrier metal connection fixtures must be provided with minimum 5 microns thickness of zinc plating and steel required to be mechanically galvanised with minimum 7.5 microns thickness.
• External steel barrier connection fixtures must be hot dipped galvanised to AS/NZS 4680:2006 and AS/NZS 1214:2016. All steel fixtures for external use are required to be mechanically galvanised with minimum 42 microns thickness.
• For weather exposed applications, all metal connections, including nails, screws, bolts and brackets, should be a minimum of hot dipped galvanised (or for screws, Class 3 corrosion resistance as per AS 3566).
• For external barrier’s post-fix connection into concrete substrate, chemical anchors are to be used to mitigate risk of puncturing water proofing membrane.
• Designer should consider durability in marine or corrosive environments. AISI Grade 316 stainless steel should be used to provide resistance to corrosive agents, including chlorides and industrial pollutants. To prevent stress corrosion cracking in stainless steel caused by prolonged condensation in the presence of chlorine and acids, HCR Grade 1.4529/1.4565 should be used.
• Tradesmen must familiarise themselves with connection details/documents, current site conditions and install all fixtures in accordance with manufacturer's specifications.

New and amended provisions for AS1288-2021

Relevant building professionals are also reminded of the changes for glass structural barriers equal to or over 1,000mm (1m) in height.

New and amended provisions in relation to the construction of those barriers includes further elaborated requirements for:

• the glass structural barriers with interlinking handrails under Section 7.4.5 (previously Section 7.3.5, AS 1288-2006).
• the glass structural barriers with no handrail or non-load supporting handrail with detailed requirements for spigot-fixed, point-fixed and core drilled barriers and use of fixing channels under Section 7.4.6.

Example – DtS pathway for internal stairs for a Class 1a building

H5D2 and H5D3 are the relevant DtS Provisions covering the structural design of the stair and barriers.

From the Australian Building Codes Board (ABCB) Housing Provisions Standard, ‘Clause 11.2.2(1) Stairway construction’ and ‘Clause 11.3.4(11) Construction of barriers to prevent falls’ requires stairways and certain barriers to be designed to take loading forces in accordance with AS/NZS 1170.1.

To demonstrate that a stairway and barrier has been designed to comply with AS 1170.1, the RBS requires, as part of the building permit application, design documentation detailing the above and including calculations. Additionally, pursuant section 238 of the Act, the RBS may rely on a certificate of compliance from an endorsed civil engineer certifying that the design complies with AS/NZS 1170.1.

To rely on a section 238 certificate in good faith, the RBS should ensure that the relevant standards are referenced on the certificate including but not limited to AS/NZS 1170.1 and other standards/documentation that have been relied upon, such as Australian Standards or documentation that provides the stair and barrier material properties and that the design caters for the project specific substrates.