Are you building a stairway and balustrade that complies with the Building Code of Australia (BCA)?
To ensure the safety of people moving between different levels of a building via ramps or stairs, the BCA specifies requirements for stairways and balustrades in clause D2.16, and handrails in clause D2.17.
The requirements for staircases include that the ‘going’ (step width forward) must be no more than 355mm, and no less than 240mm for private stairs, and no less than 250mm for public stairways.
An open staircase must also be built so that a 125mm sphere cannot pass through the treads. This safety precaution ensures that a young child’s head cannot become caught between the stairs.
A continuous balustrade or other barrier must be provided along the side of any stairway where the level above the surface beneath is 1000mm or more. Every stairway must have at least one handrail with a smooth continuous top surface throughout the length of each stairway flight. Where the width of the stairway exceeds 1000mm, a handrail must be provided on each side.
Balustrades located in different types of non-residential buildings that are accessed by people with disabilities must be designed to the requirements covered in AS 1428.1-2009, Design for access and mobility – General requirements for access – New building work, for stairways (Clause 11.1) and handrails (Clause 11.2).
Landings are an important factor in building a staircase and must be designed and constructed in accordance with the requirements of Clause 3.3. The length and the width of the landing cannot be less than the width of the stairway, and must have a minimum vertical clearance of not less than 2000mm.
Every access landing must also provide standing space of at least 600mm clear of cross-traffic or opening doors. The code dictates that stairways must have not more than 18 risers (step heights), or less than two in each flight, with a riser dimension of no less than 115mm and no more than 190mm.
Structural Glass Balustrades
The increasing popularity of glass balustrades has led to the Australian Standards inclusion of a completely new section dedicated to this classification AS 1288 - 2006 Glass in Buildings – Selection and installation (Section 7). This in turn created further need for design loads and other actions to be addressed in AS/NZS 1170.0, AS/NZS 1170.1 and AS/NZS 1170.2.
In all balustrades where glass is the structural component of the balustrade the glass must be Grade A Safety glass.
AS 1288-2006 Section 7.3.5 requires that Structural Balustrades – All types – Protecting a difference in level to, or greater than 1000mm, require an interlinking handrail. This is the most miss-understood concept when it comes to structural glass usage on stairways
Section 7.3.5 directs the reader to Table 7.1, which specifies the thickness of glass to be used, based upon the design load.
For a domestic stair and void area (Type A) AS 1170.1, Table 3.3 specifies design loads of 0.35kN/m horizontal and vertical and 0.6kN point load on the top edge of the glass.
Returning to Section 7.3.5, Table 7.1 for 12mm glass, the maximum height of the glass should be 1030mm (0.6kN/m) from the top of the glass to the top point of the base glass fixing.
In other words, for a 12mm thick toughened glass balustrade on a domestic stair, the handrail must be continuous around the corner where the level meets the slope and each piece of glass must be specified as a minimum of 1000mm wide, or the handrail must continue onto, and be fixed to, the floor.
One of the most discussed standards is in respect to the occupancy of a building and concerns the areas where people may congregate. AS/NZS 1170.1 Table 3.3 sets out the required design loads for ‘Minimum Imposed Actions for Barriers’ for different types of occupancy. These are:
TYPE C1/C2 - Areas with tables of fixed seating with specific use adjacent to balustrade, restaurants, bars etc.
TYPE C3 – Areas without obstacles (such as tables and chairs) used for moving people and not susceptible to overcrowding and with specific use as Stairs, landings, external balconies, edges of roofs, etc.
TYPE C4 – Areas with possible physical activities such as dance halls, gymnasia and drill halls and drill rooms – not applicable to Table 3.3.
TYPE C5 – Areas susceptible to over-crowding such as theatres, cinemas, grandstands, discotheques, bars, auditoria, shopping malls, assembly areas, studios, etc.
Design requirements range from 1.5 kN/m to 3.0 kN/m on the horizontal top edge of the barrier and from 0.5kN to 1.5 kN in any direction on the infill of the barrier as specified in the table.
Builders are advised to request confirmation of certification of design, signed off by a qualified engineer, from their balustrade supplier.
This brief overview of some of the requirement in the building code that affect building stairways and balustrades should not be seen as a guide to the Australian Standard.
Yes, it’s complicated!! So the best advice is to consult with a practitioner in this field.
References: Australian Standards
AS-1288-2006 Glass in buildings—Selection and installation
AS 1428.1-2009 Design for access and mobility - General requirements for access - New building work
AS/NZS 1170.0:2002 Structural design actions—General Principles
AS/NZS 1170.1:2002 Structural design actions—Permanent, imposed and other actions
AS/NZS 1170.2:2002 Structural design actions—Wind actions