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Installing a cantilevered staircase starts with the wall and the building structure, not with the visible treads. Arden Architectural Staircases’ technical advice, published by Architecture & Design on 20 June 2010 and reproduced in the Spec-Net archive, recommends bringing the structural engineer and staircase supplier into the project during design. The engineer confirms the structure can receive the cantilever load; the supplier protects the stair’s space in the floor plan and develops a support assembly suited to the wall, cavity and finishes.
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Arden’s methods are project-specific guidance from 2010, not current building-code instructions. Its dimensional figures—including a 125 mm maximum tread gap attributed to Australian regulations, a 190 mm maximum rise, and a 65 mm minimum tread thickness—must be checked against the code and authority having jurisdiction for the actual project.
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A conventional stair usually shows a visible stringer, beam or series of supports beneath the treads. A cantilevered flight hides most of that structure. Each tread projects from a supporting wall or concealed frame, creating the floating appearance that designers want. The visual simplicity does not mean the engineering is simple: the wall, connections, steelwork, floor openings and balustrade all participate in the load path.
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In Arden’s description, the tread support is concealed in or against the wall. Loads from people, finishes and the handrail travel through the tread support into the wall and then into the building structure. That makes the supporting wall a structural component of the stair, even when it looks like an ordinary partition after plastering.
The right arrangement depends on the wall’s strength, the space available behind the finished plaster line and the geometry of the flight. A support detail that works in a reinforced masonry wall may be unsuitable for a lightweight framed wall. Treat the options below as design routes to investigate with an engineer and experienced stair fabricator, not as interchangeable kits.
Coordinate the stair before the floor plan is fixed
Arden’s first recommendation is to consult the structural engineer responsible for the main structure. The purpose is to verify that the building can take the cantilever load transferred to the wall. This review should occur before finishes, openings and framing are treated as settled decisions.
Arden also advises consulting the preferred stair supplier early enough for the flight’s space requirements to be included in the floor plans. The supplier needs room for the stair width, landing geometry, concealed steel, wall build-up, plaster or other finishes, construction tolerances and any balustrade components. Moving the stair after the structure is framed can force compromises in headroom, tread alignment or wall thickness.
Early-coordination checklist
- Identify the structural engineer responsible for the primary building structure.
- Give the engineer the proposed flight geometry, tread loads, wall location and connection concept.
- Ask the stair supplier to reserve the stair opening, landings and service clearances in the floor plans.
- Draw the finished plaster line and every concealed support zone, not just the nominal wall centreline.
- Coordinate floor, ceiling and landing levels before fabrication drawings are approved.
- Record who designs, supplies and certifies the supporting wall and its connections.
This sequence follows Arden’s advice that structural adequacy and space planning are decisions made together. A supplier brought in after construction begins may be unable to fit the intended support without rebuilding the wall.
Choose the support route by wall condition and cavity depth
Arden describes three broad approaches. The first is for a heavy structural wall with sufficient room for the plaster line. The second addresses a cavity that cannot accommodate the required plaster-sheet offset. The third is for lightweight wall framing, which needs a deliberately strengthened construction rather than standard studs.
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| Wall or site condition | Support approach described by Arden | Coordination issue to resolve |
|---|---|---|
| Heavy structural wall with room behind the finish | Tread supports welded to a mild-steel SHS frame fixed to the wall | Confirm wall capacity, frame anchorage, weld and connection detailing, and the finished plaster offset. |
| Stair cavity cannot accommodate the plaster-sheet offset | Steel plate stringers that sandwich the wall, connected through the wall | Reserve the through-wall connection zone and coordinate plates with finishes, services and the opposite face of the wall. |
| Lightweight framed wall | A designed double-framed wall incorporated into the stair construction component; Arden describes structural plywood on both sides of a timber frame or a complete structural steel frame. | Do not rely on ordinary wall framing. Design the frame, sheathing, anchors and load transfer as one structural assembly. |
The table shows why a “floating stair bracket” chosen without the wall design is risky. The support must fit the cavity and transfer forces into a structure that was designed for them. A later manufacturer guide makes the same broader point: wall capacity, load transfer, connection detailing and coordination should be checked before the stair is finalized. That guidance is context, not a replacement for a local engineer’s design.
Heavy structural wall with a concealed SHS frame
Where the wall is heavy and the finish build-up leaves adequate room, Arden describes tread supports welded to a mild-steel square hollow section (SHS) frame fixed to the wall. The SHS frame acts as the concealed backbone for the individual tread supports. The engineer must establish how the frame is anchored, how forces spread through the wall and how the wall connects to the rest of the building.
Before closing the wall, verify the frame’s position against every tread datum. Small errors in elevation or rotation become obvious when the treads are installed in an otherwise empty-looking flight. Provide a documented survey or inspection point so the stair supplier can confirm the steel is where the fabrication drawings require it.
Through-wall plate stringers when the cavity is tight
If the cavity cannot accept the plaster-sheet offset required by the first arrangement, Arden describes steel plate stringers that sandwich the wall and use through-wall connections. This approach can keep the stair geometry while placing steel on both faces of the wall.
Through-wall steel changes the finishing and waterproofing conversation. The design team must coordinate bolt or plate penetrations, fire and acoustic requirements, services, access for tightening or inspection, and the finish on the opposite side. The wall cannot be treated as a simple backdrop once it is clamped between structural plates.
Strengthened double framing for lightweight walls
Lightweight framing requires a designed support solution. Arden advises incorporating a double-framed wall into the stair construction component. The article identifies two examples: structural plywood fixed to both sides of a timber frame, or a complete structural steel frame.
The important idea is continuity. Studs, plates, sheathing, fasteners and the connection to the surrounding structure must be designed to carry the stair forces together. Standard wall framing may be too weak, too flexible or too imprecise for a cantilevered flight, even if it can support ordinary plasterboard and nonstructural loads.
Make the supplier’s scope explicit
Arden recommends a provider with a track record in engineered stairs. It warns that standard wall framing can be insufficiently strong or precise and suggests that the stair supplier include the supporting wall in its scope of work.
Including the wall in the supplier’s scope reduces the gap between the person designing the tread steel and the person building the structure that receives it. The contract and drawings should state which party is responsible for:
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- Design of the wall frame, SHS backbone or plate-stringer connection.
- Fabrication tolerances and site verification.
- Anchors, bolts, welds, plates, sheathing and corrosion protection.
- Temporary support during construction.
- Coordination of plaster, skirting, flooring and other finishes.
- Balustrade posts, glass channels or other guard components attached to the stair.
Ask for shop drawings that show the wall build-up, finished face, tread projection, connection locations and inspection points. A supplier’s portfolio is useful, but it does not replace project-specific calculations or approval by the responsible engineer.
Use Arden’s dimensions as dated design assumptions, not universal rules
Arden’s 2010 guidance includes several figures that are often repeated in discussions of open stairs. They need careful qualification:
| Figure | What Arden’s 2010 advice says | How to use it now |
|---|---|---|
| 125 mm maximum gap between treads | Attributed by Arden to Australian regulations. | Check the current code for the project’s jurisdiction and the exact opening, guard and handrail provisions. Do not treat the 2010 attribution as current legal confirmation. |
| 190 mm maximum rise | Stated by Arden as an assumption for its fully open-flight discussion. | Verify the current dimensional limits, permitted variations and measurement method with the local authority or code professional. |
| 65 mm minimum tread thickness | Stated by Arden in the same fully open-flight assumptions and conclusion. | Confirm the required structural thickness and finish build-up through the engineer’s design and current code. |
| About 70 mm overall tread thickness | Arden’s description of a typical composite tread using a 40 mm mild-steel SHS structural-frame core. | Treat it as Arden’s typical specification, not a general standard. Actual thickness depends on span, materials, finish and engineering. |
These numbers cannot establish compliance by themselves. Codes change, jurisdictions differ and authorities may measure a gap, rise or tread in a particular way. The engineer and building-control process should determine the dimensions that govern the project.
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Design the balustrade with the stair, not after it
The balustrade is part of the visual and structural design. Arden says an architect, designer or staircase contractor should help select a suitable style that does not detract from the clean lines of the flight.
Decide early whether the design uses glass, vertical elements, a slim rail or another treatment. Each choice affects attachment points, edge distances, local reinforcement, sightlines and the apparent thickness of the floating treads. A balustrade fixed to the stair may introduce forces that the tread support was not originally arranged to receive, so show those forces in the engineering brief.
Do not infer current guard height, handrail height, opening size or loading requirements from Arden’s article. The 2010 advice does not establish those dimensions for any particular jurisdiction. Obtain the applicable current requirements before fabrication.
A practical design-and-installation sequence
- Define the architectural intent. Set the flight width, landing locations, tread finish, open-side treatment and desired visual gaps.
- Map the structure. Identify the wall, floor framing, landings and any elements that can receive the cantilever reactions.
- Bring in the engineer. Have the responsible structural engineer assess wall capacity and the load path into the main structure.
- Bring in the stair supplier. Confirm space requirements, fabrication limits, support strategy and whether the wall is included in the supplier’s scope.
- Select the wall-specific route. Choose the SHS frame, through-wall plate stringers or designed double framing only after the cavity and finish depth are documented.
- Coordinate finishes and services. Reserve space for plaster, flooring, skirting, fire and acoustic treatments, lighting and any concealed services.
- Issue coordinated drawings. Show tread levels, support steel, anchors, wall layers, balustrade attachments, tolerances and inspection points.
- Verify the built support before covering it. Check location, alignment, fasteners and welds against the approved drawings before plaster or sheathing hides the work.
- Install treads and balustrade in the approved sequence. Protect finished surfaces and avoid loading incomplete supports or unbraced components.
- Complete the authority checks. Confirm the final dimensions and guarding meet the current local requirements before use.
Common failure modes and how to prevent them
The wall was treated as nonstructural
Symptom: The design assumes ordinary studs or a thin partition can receive the stair. Prevention: Have the engineer design the wall and its connection as part of the stair system; use the double-framed timber-and-plywood or steel-frame approach described by Arden where appropriate.
The cavity is too shallow for the intended support
Symptom: The steel conflicts with the plaster line, services or the opposite finish. Prevention: Draw the complete wall build-up early and investigate a through-wall plate-stringer arrangement if the cavity cannot accommodate the first option.
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Symptom: The opening, landing or wall thickness no longer matches the fabricated stair. Prevention: Reserve the flight’s space during floor-plan design and require coordinated shop drawings before construction.
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Tread alignment is inconsistent
Symptom: Floating treads show uneven gaps or a visible change in level. Prevention: Set out every support from a common datum, inspect the concealed steel before closing the wall and record site tolerances.
The balustrade was added as an afterthought
Symptom: Posts, channels or fixings interrupt the clean lines or lack adequate support. Prevention: Select the balustrade with the architect, designer or stair contractor and include its loads and attachments in the engineering drawings.
What Arden’s “beautiful, economical and safe” claim means
Arden’s take-home wording says, “Don’t worry! With a little planning and the right approach, cantilevered flights are beautiful, economical and safe.” That is Arden Architectural Staircases’ promotional statement in advice published by Spec-Net, not an independent safety finding or a guarantee for every project. The defensible takeaway is the planning principle behind it: a cantilevered stair can achieve its intended appearance only when structure, wall construction, supplier scope, finishes and guarding are coordinated before installation.
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When a cantilevered stair is the wrong fit
A floating stair may be a poor choice when the supporting wall cannot be strengthened, when the floor plan cannot reserve the required cavity, or when the project cannot accommodate the engineering and inspection needed for concealed connections. A visible stringer or independently supported stair may offer a more straightforward load path and simpler construction. That decision belongs to the project team after comparing structure, space, appearance, programme and approval requirements.
For a feasible project, the next action is not ordering a generic bracket or tread. It is assembling the engineer, experienced stair supplier and design team around the wall-specific support detail, then checking that detail against current local regulations.
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