Closed steel mono-stringer with full tread and riser assembly

Almost a decade ago, Arden streamlined the domestic mono-stringer design for broad application in the Australian market, and with good reason this staircase format has become an industry standard.

Almost a decade ago, Arden streamlined the domestic mono-stringer design for broad application in the Australian market, and with good reason this staircase format has become an industry standard. The M1 evolves this basic structural technique to create a fully fledged commercial design. The intent of the M1 is to create a proportionally significant and deceptively simple interior sculpture. Attention is drawn to the contrast in the snaking zigzag of warm polish timber and the linear sweep of the structural steel member, thus emphasising a simultaneous contrast in line and material.

By default, the M1 incorporates a thick monolithic hardwood tread and riser assembly so that no edge trim is required, and avoiding any possible distraction from the clean geometric lines of the staircase. The mono-stringer's position underneath and away from the edges of the treads makes it retreat from view, and allows the impression of the staircase to be dominated by the zigzag tread and riser assembly when viewed from a forward position.

Leveraging the strength of structural steel, the central beams of the mono-stringer can span large open spaces without support. Due to its visual simplicity, it can sit equally well in a modern office or public building; either alone, or surrounded by other structure. On exceptionally long spans a central column is applied to add the necessary support, while to maintaining a slim metal stringer line.


The core member of the M1 is constructed from SHS or RHS mild steel sections of a size suitable for the required loads and spans. These sections are mitred and welded at the angle points into a continuous solid member. Support plates for the treads and landings are welded to the core. Mounting plates are also usually welded where required at this stage.

While most mono-stringers only need two support points per flight, it must be kept in mind that the structure must provide strong rotational, as well as lateral and vertical support. Support bindings are usually in the form of a steel mounting plate with at least 4 points for bolts or other attachments. In some cases, the stringer can be welded directly to steel support beams in the existing structure.

Two alternative tread designs are shown. The first shows a solid timber tread. If larger treads are required, solid wood of the required profile may be difficult to source. In this case, an alternative composite tread is applied, comprising a veneer of dress timber over a structural ply or MDF core. Other designs and materials are possible: refer to Arden technical data sheet ‘A.3 Treads’ for details.

There are also two alternative tread support plate designs. Light duty stairs may use the folded tread plate design. Where high design loads or a wide flight is specified, a heavier gauge steel tread plate is called for. This would make a folded design impractical, and we would therefore recommend the use of the two piece orthogonal welded design.


Arden Architectural is a BSA licensed contractor for carpentry, joinery, glass, glazing and aluminium as well as structural metal fabrication and erection. Arden supplies a Form 16 (Licensed Contractor) on all projects. In design and construct contracts, a Form 15 (Design Engineer) certification is supplied upon request. For products and services incorporating this design element, the table below details compliance with relevant codes and standards.

Title Applicability
BCA The Building Code of Australia Full compliance
AS NZS 1170.1-2002 Structural Design Actions – Permanent, imposed and other actions Full compliance
AS 1288-2006 Glass in Buildings. Selection and installation Not applicable
AS NZS 1554.1-2004 Structural steel welding - Welding of steel structures Full compliance
AS 1554.6-1994 Welding stainless steels for structural purposes Full compliance
AS NZS 4586-2004 Slip resistance classification of new pedestrian surface materials Full compliance
AS 1428.1-2001 Design for access and mobility Full compliance
AS 1657-1992 Fixed platforms, walkways, stairways and ladders. Design,
construction and installation
Full compliance