A mono-stringer staircase uses a single central steel beam to support all treads — the “spine” runs beneath each step, and treads project symmetrically left and right with no visible side framing. It is the structural system that creates the true floating visual that defines contemporary Ontario staircase design. This guide covers what makes a mono-stringer different from other structural systems, what OBC and engineering require, and what it costs in Ontario in 2026.
What Is a Mono-Stringer
The word “mono” means single — one stringer, running centrally beneath all treads. This single beam must carry the full structural load of the staircase: the weight of the treads, the live load from people using the staircase (OBC Part 9 design live load: 1.9 kPa for residential stairs), and the lateral load from the railing system.
Because all load is concentrated in a single beam rather than distributed across two stringers, the mono-stringer must be larger in cross-section than each individual double-stringer beam. A structural engineer specifies the beam size, connection at the base plate (anchor to floor framing), and connection at the top (anchor to landing or upper floor framing).
Visual Difference vs. Double-Stringer
| Mono-Stringer | Double-Stringer | |
|---|---|---|
| Structural beams visible from front | None — only the central spine below | Two beams along tread edges |
| Tread visual | Appears to float — no side framing | Open riser, but framing visible |
| Best viewing angle | Front elevation — maximum floating effect | Front elevation — beams visible |
| Engineering review required | Yes — P.Eng letter required for Ontario permit | Standard structural calc |
| Ontario cost premium | +15–25% over double-stringer | Baseline |
| Suitable clear width | Up to 1,100 mm recommended | Over 1,100 mm preferred |
Ontario Engineering Requirements for Mono-Stringer Staircases
A mono-stringer staircase permit application in Ontario must include a structural engineer’s (P.Eng) stamped letter confirming:
- Steel section size (e.g., HSS 100×100×9.5, W150×22, or similar — specified by the engineer based on tread span, number of risers, and design live load)
- Base plate connection details — anchor bolt size, embedment depth, concrete or wood framing substrate
- Top plate connection — how the beam is connected to the upper landing or floor framing
- Tread bracket specification — weld size, bracket material, bracket-to-tread fastener pattern
- Deflection confirmation — that the beam will not deflect more than OBC-permitted amount under design live load
C.O.R.S includes the P.Eng engineering review and stamped letter in every mono-stringer project quote. You do not manage this separately — we have an established engineering relationship and the letter is delivered as part of the permit package.
Mono-Stringer Fabrication Sequence
- Steel beam cut to the overall stringer length from the engineer-specified section
- Step positions laid out on the stringer to within 1–2 mm of the design specification
- Tread brackets welded at each step position — welds inspected for consistency
- Bracket alignment confirmed with a straightedge across the full flight
- All welds ground flush — no visible weld bead on any finished surface
- Stringer sandblasted, primed, and powder-coated matte black, oven-cured
- Workshop dry-fit: stringer, treads, railing assembled and verified
2026 Ontario Cost — Mono-Stringer Staircases
| Configuration | Treads | Railing | Installed Price |
|---|---|---|---|
| Straight mono-stringer | White oak 38mm | Glass (post-channel) | $14,000–$20,000 |
| Straight mono-stringer | Walnut 38mm | Glass (post-channel) | $17,000–$24,000 |
| L-shaped mono-stringer | White oak 38mm | Glass (post-channel) | $18,000–$26,000 |
| L-shaped mono-stringer | Walnut 38mm | Glass (post-channel) | $22,000–$30,000 |
All prices include design drawings, P.Eng engineering review, permit drawings and application management, fabrication, workshop dry-fit, delivery, and installation.
→ Full floating staircase Ontario guide — all structural systems
→ Mono-stringer floating stairs in Barrie Ontario — local cost and permit guide
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