The stringer is the most critical structural element of any steel staircase. It carries every load from the weight of the treads to the live load of people using the stairs and its type, size and configuration determine both the structural performance and the visual character of the finished staircase.
Choosing the wrong stringer type leads to either an over-built, expensive staircase or, worse, an under-built one that won’t pass structural inspection. Here’s what you need to know.
A stair stringer is the inclined structural member that runs alongside (or beneath) the stair treads, supporting them from the bottom step to the top landing. In a steel staircase, the stringer is typically a fabricated steel section welded, cut and prepared to accept the tread fixing points.
1. Mono Stringer (Single Central Stringer)
A mono stringer runs down the centre of the staircase, a single steel section that supports both treads from the middle outward. Treads cantilever either side of the stringer, creating an open, floating visual that’s distinctive and contemporary.
Best for: Residential homes, architectural feature staircases, contemporary interior design, anywhere an open and minimalist aesthetic is the goal.
Load capacity: Adequate for residential live loads (typically 2.0 kPa to 3.0 kPa). Not suitable for heavy commercial or industrial use.
Visual character: Slim profile, lightweight appearance. The staircase appears to float. Very popular in modern Australian homes.
Consider: Tread overhang must be calculated carefully. Lateral stability requires connection at both top and bottom and careful tread-fixing design.
2. Double Stringer (Twin Side Stringers)
Double stringers run parallel down either side of the staircase, supporting the treads between them. This is the most common stringer configuration for commercial, industrial and standard residential applications it’s strong, predictable and easy to detail and fabricate.
Best for: Commercial buildings, industrial facilities, warehouses, mezzanine access, public buildings any application where reliability and load capacity are the priority.
Load capacity: Suitable for commercial and industrial live loads (4.0 kPa+) when correctly engineered and sized.
Visual character: More substantial and traditional looking than a mono stringer. Can still look clean and modern depending on the section profile and finish.
Consider: Width between stringers must accommodate your tread width. Stringer height determines the visual weight of the staircase.
3. Box Stringer
A box stringer is a hollow rectangular (RHS) section stringer a fully enclosed profile that presents a clean, solid face. Box stringers have a distinctive, architectural quality that suits high end commercial and contemporary residential applications.
Best for: High end commercial fit-outs, architectural residential staircases, hospitality and retail environments where the staircase is a design feature.
Load capacity: High the closed section provides excellent torsional stiffness.
Visual character: Solid, strong, modern. The clean rectangular profile reads as a design element in its own right. Pairs very well with glass balustrades and feature lighting.
Consider: Fabrication is slightly more complex than open sections, which can affect cost and lead time.
4. C-Channel Stringer
A C-channel (PFC: Parallel Flange Channel) stringer is an open-section structural channel used in many industrial and commercial stair applications. C-channel stringers are cost-effective, strong and widely used in situations where structural performance matters more than visual refinement.
Best for: Industrial warehouses, factories, mezzanine access stairs, fire escape structures, utility and access staircases in commercial buildings.
Load capacity: High C-channel sections are efficient in bending.
Visual character: Functional rather than decorative. Best suited to environments where the staircase is a tool, not a feature.
Consider: The open section profile is less visually refined than box or mono stringers. For anything visible from a main entrance or public area, a more architectural option may be worth the investment.
Work through these questions:
1. What is the primary use of the staircase? Residential home → mono or double stringer Commercial building → double or box stringer Industrial warehouse → double stringer or C-channel
2. What live load does the staircase need to carry? Residential (families, occasional visitors) → 2.0–3.0 kPa → mono or double stringer Commercial (regular public foot traffic) → 3.0–5.0 kPa → double or box stringer Industrial (heavy tools, equipment, machinery parts) → 5.0 kPa+ → double stringer or C-channel, heavily engineered
3. What does the finished staircase need to look like? Contemporary and architectural → mono or box stringer Clean and neutral → double stringer Functional and industrial → C-channel
4. What is your budget? Most economical → C-channel double stringer Mid-range → double stringer (UB or PFC section) Higher investment → mono stringer or box stringer
Choosing the type of stringer is one decision choosing the right size for that type is another, and it must be done by a structural engineer. The engineer calculates the span, load and required section modulus to determine the minimum steel section that will safely carry the staircase load. Never skip this step.
At Sydney Structural Steel, our team works with your engineer to confirm stringer sizing as part of the shop drawing process. If you don’t have an engineer, we can refer you to a qualified structural engineer to complete the design.
Sydney Structural Steel fabricates all four stringer types for residential, commercial and industrial staircases across Sydney and NSW. Call [+61] 296154777 or visit sydneystructuralsteel.com.au/
