Stair systems
Layouts
Residential
Straight mono stringer →Cable & metal
Wood & combinations
Frameless glass →Tread profiles
Solid white oak →Stair lighting
Light under every tread →Who we work with
Stair systems
Mono stringer
Layouts
By material
Residential
Commercial
All floating stairs →Tread materials
Wood species
Tread profiles
Finishes
Who we work with
Work with us
Specifications
One line, rising.
One rolled steel spine follows the curve, and tapered solid-wood treads sweep around it. No corner, no landing: the stair turns as you climb. Engineered, permitted and installed in NYC, Long Island and New Jersey, from $46k in NJconfirm.
A curved mono stringer is a floating stair built on one central steel spine that is rolled to a helix in our shop. Every tread is tapered, narrow on the inside of the curve and wide on the outside, and sits on its own steel saddle on top of the spine. You never meet a corner: the stair turns a little with every step.
The rolled spine · one closed steel box, bent to the curve, saddles shop-welded
A curve shows everything: the line of the spine, the taper of every tread. The details people notice first.
Both stairs turn as you climb. The difference is the radius and where the steel goes. The line is the path your feet follow.
A wide, gentle radius: about 4′-6″ to the inside of the treads. One rolled spine sits under the middle of every tread, so the treads float on both sides. Each tread is about 9″ deep at the narrow end and 11″ on the walking line, so it walks like a straight stair.
A tighter radius, often turning 270° or more around an open eye. The treads hang between two rolled stringers, an inner and an outer one, so the steel frames the stair instead of hiding under it. It takes less floor and makes a sculpture of the stringers.
Both plans: 10′ floor to floor, 42″ treads, 7½″ risers. Prefer a corner? A winder mono stringer turns 90° on three tapered treads in about 9′ × 9′. All curved layouts: curved floating stairs →
The spine, the saddles, the glass and the handrail are drawn together as one curve, not fitted on site.
A closed steel box, rolled on a three-roll machine to your exact radius and pitch, then checked against a full-size template. A closed box resists the twist a curve creates; an open beam would not. Long spines are rolled in two pieces and joined with a hidden bolted splice.
Every tread is cut from solid 3¾″ wood to the same wedge: about 9″ at the narrow end, 11″ on the walking line, 16″ at the wide end. Each sits on a welded saddle hidden 1½″ inside the edges, so the tread looks like it floats.
Flat frameless panels, one for every two or three treads, set ½″ apart, trace the curve on both open sides. The handrail is rolled to the same helix and runs in one line, 34–38″ above the nosings, so your hand never lets go.
Pick your floor height, how wide the curve is and which way it turns. The plan and the numbers redraw to the same rules our engineer uses.
Inner radius 4′-6″: every tread is at least 6″ deep at the narrow end and 11″ on the walking line, inside the residential code in NJ, Long Island and NYC.
A straight spine only bends. A curved spine also twists, because the middle of the stair sits away from the line between its two ends. Tap a step to follow the weight.
Reactions are for a typical 10′ curved stair in white oak and are illustrative. A licensed PE sizes the spine, the splice and every connection for your stair and your floor.
| Component | Specification |
|---|---|
| Spine | One closed steel box, HSS 10×6 typical, or a fabricated plate box, rolled to the stair’s radius and pitch |
| Splice | Over about 20′, rolled in two pieces with a hidden bolted splice |
| Saddles | One welded steel saddle per tread, hidden 1½″ inside the tread edges |
| Treads | 42″ wide, 3¾″ solid wood, tapered: ≈ 9″ inside, 11″ on the walking line, 16″ outside |
| Rise × run | 7–7½″ × 11″ on the walking line. Open riser gap ≤ 3¾″ |
| Top | ¾″ header plate, through-bolted. A moment connection, not a hanger |
| Loads | 40 psf, plus 300 lb on any tread, checked for bending and twist |
| Stiffness | L/480 along the spine, first frequency 8–10 Hz or more |
Choose the tread species, the spine finish and the lighting as one coordinated palette. Every tapered tread is cut from the same boards, so the grain flows around the curve.
Matte black
White
Bronze
An LED channel under the nose of every tread, wiring hidden inside the spine, one dimmable driver. Motion sensors and tunable white are options. +$1.5–4k.
Your electrician brings power to one box at the base of the spine. We do the rest.
Under-tread stair lighting →The railing sets how open the stair feels and what your hand holds. Guards follow the curve on both open sides, and the handrail is rolled to the same helix as the spine.
Gaps under 4″ everywhere. All railings → · Glass railings → · Cable railings →
One geometry. Change the wood, the spine and the railing, and the room changes with it.
Floor height, radius and sweep, tread species, railing, finishes, lighting and the delivery route.
See prices ↓The rolled spine goes in first, checked against the template, then the treads one by one. Full timeline →
Installed prices: design, PE engineering, fabrication, powder coat, delivery and installation. Permit fees and co-op deposits are billed at cost.
| What moves the price | Effect | What moves the price | Effect |
|---|---|---|---|
| LED under every tread | +$1.5–4k | Walnut tapered treads | +$3–5k |
| Tighter radius or longer sweep | quoted | Brushed stainless spine | +40–60% on steel |
| Bent (curved) glass instead of flat panels | +$10–20k | Heights over 12′ | +$1.5–2k per tread |
Rolling the spine, the tapered treads and the faceted glass add about $16–22k over a straight mono stringerconfirm. Curved staircase cost →
| New Jersey · 1–2 family 2024 IRC as amended | Long Island NYS Residential Code | New York City · R-3 2022 NYC Building Code | |
|---|---|---|---|
| Max riser · min tread | 8¼″ · 9″ | 8¼″ · 9″ | 8¼″ · 9″, and 2 risers + 1 tread ≤ 25½″ |
| Max rise of one flight | 12′-7″ | 12′-7″ | 12′-0″ |
| Headroom, along the whole curve | 6′-8″ | 6′-8″ | 80″ |
| Guard along the flights | 36″ | 36″ | 34″ |
| Guard at the floor opening | 36″ | 36″ | 42″ |
| Tapered (curved) treads | 9″ on the walking line, 6″ min | 10″ on the walking line, 6″ min | 10″ 12″ from the narrow end, 6″ min |
| Smallest radius | no minimum | no minimum | no minimum in R-3 homes; 2 × stair width elsewhere |
An open stair joining 3–4 floors of an NYC townhouse may also need sprinklers. Are floating stairs legal in NYC? →
A floating stair is a big decision. Here is what we put in writing.
Standard curved details as a starting point: base, rolled spine, splice, tread saddle, tapered tread geometry and header. We produce PE-stamped shop drawings for your approval.
Still unsure? Send a photo of your stairwell and we'll tell you what fits.
A floating stair built on one central steel spine that is rolled to a curve. Every tread is tapered and sits on its own welded saddle on top of the spine, so both sides of the stair float and it turns a little with every step.
Yes. Inside one- and two-family homes and dwelling units, curved stairs follow the winder rules: each tread at least 10″ deep on the walking line, 12″ from the narrow end, and never less than 6″ (NYC BC §1011.5.2–1011.5.3 and the NJ residential code). Our standard curve gives about 9″ at the narrow end and 11″ on the walking line.
For a 10′ floor-to-floor height on our standard curve (4′-6″ to the inside of the treads), the stair sweeps about 143° and needs about 15′-2″ × 6′-7″ of floor, plus 3′ clear at the bottom step. Use "Designed around your space" above for your height and radius.
A curved mono stringer has a wide radius and one spine under the middle of the treads. A helical stair has a tighter radius, often turning 270° or more, with two rolled stringers framing the treads. See helical stairs.
Not when it is sized right. The spine is a closed steel box, which resists twist, and it is moment-connected to the upper floor. We design for L/480 and 8–10 Hz or more, and add a slim column under the curve only when a long sweep needs it.
Usually. A rolled spine cannot bend around a doorway, so long spines are rolled in two pieces and joined with a hidden bolted splice. We check the delivery route, including stoops and elevators, before fabrication.
From about $46k installed in New Jersey and $54k in New York City for a 9–10′ stair with oak treads and a cable or rod guard. With frameless glass, about $58–78k in NJ and $66–88k in NYC. Final price after we measure.
Floor plans, the floor-to-floor height, photos of where the stair starts and arrives, and the way in: doors, stairs or elevator the spine has to pass.
Your height and curve from above are already filled in. Add a photo of each end of the stair.
