Types of Steel Staircases: Straight, L, U and Spiral

Steel staircases come in a handful of layouts (straight, L-shaped, U-shaped, spiral and curved) and a handful of structural types (two side stringers, a single central stringer, folded plate and cantilevered treads). The layout is decided by the space and the floor-to-floor height; the structure is decided by the look you want and what the stair can be fixed to. In Ontario, every type has to meet the same Building Code rules for rise, run, width, headroom, handrails and guards, and some types, like spirals and winders, have extra rules or limits on where they can be used.

This guide walks through each type, where it fits, and the code points that come with it. For the full rule set, see Ontario Building Code rules for steel stairs.

Steel staircase types by layout

Straight steel stairs

A straight stair is the simplest to design, fabricate and install. Two stringers run from floor to floor with treads between them, and nothing has to turn. The limit is height: under the 2024 OBC, a single flight can't rise more than 3.7 m without a landing, so a tall straight stair becomes two flights with a landing in a line. Straight stairs are also the easiest to get through a door and into place, which matters on renovations.

L-shaped steel stairs

An L-shaped stair turns 90 degrees, either at a landing or with winders. A landing is the usual choice and the only option outside a dwelling unit. Winders (tapered treads that turn the corner) are allowed only in stairs within dwelling units, and the OBC limits them: the set turns no more than 90 degrees, each tread turns 30 to 45 degrees, and adjacent winders turn through the same angle. A steel L-stair is often built as two straight stringer sets bearing on a steel-framed landing, which can be supported by posts or by the walls.

U-shaped steel stairs

A U-shaped or switchback stair turns 180 degrees at an intermediate landing, so the two flights run side by side. This is the standard layout for commercial exit stairs and multi-storey stairwells because it stacks floor after floor in the same shaft. In steel, U-stairs are often pan stairs with concrete-filled treads; see what are steel pan stairs. The landing is usually framed in channel and hung from the floor above, carried on posts, or bolted to the shaft walls. Our guide to steel stair landings covers when you need one and how they are supported.

Spiral and curved steel staircases

Spiral stairs

A spiral stair wraps its treads around a central column. It takes the least floor area of any stair, which is why it is used for lofts, rooftop access and secondary stairs. The 2024 OBC sets specific rules for spiral stairs (Article 9.8.4.7.):

• handrails on both sides, with the outer handrail at least 1,070 mm high
• clear width of at least 660 mm between handrails
• risers no more than 240 mm high
• treads at least 190 mm deep, measured 300 mm from the centre line of the handrail at the narrow edge, with a consistent angle and uniform size, all turning the same way
• at least 1,980 mm of clear height

A spiral stair that meets those rules may be the only means of egress only where it serves no more than 3 persons. Otherwise, a spiral stair cannot serve as an exit. In practice, spirals work best as a secondary stair or for a small loft or suite. Whether a spiral can be the main stair in a house depends on how many people it serves and whether it is part of the required egress, so check the use with your designer and building department before choosing one.

Spiral stairs are also hard to move furniture up. Plan another route for anything large.

Curved and helical stairs

A curved stair follows an arc without a centre post. The stringers are rolled or built up in plate to the curve, which makes them one of the most demanding stairs to fabricate and install. Where a curved flight is used in an exit, the 2024 OBC (Article 3.4.6.9.) requires a handrail on each side, a minimum run of 240 mm, treads that meet the normal run rules when measured 300 mm from the inside handrail, and an inside radius of at least twice the stair width. Under Part 9, curved flights with tapered treads are also permitted in stairs within dwelling units and in public stairs, with tread rules of their own (Article 9.8.4.3.).

Steel staircase types by structure

The layout sets the plan; the structure sets the look.

• Double stringer. Two stringers, one each side, with treads spanning between. The most common and most economical type, used for everything from basement stairs to industrial access. Stringers are usually channel or plate; see steel stair stringer sizes for sections.
• Mono-stringer (central spine). A single heavy stringer, often a box section or large HSS, runs under the centre of the treads, which cantilever out on each side. It gives the light, open look popular in modern homes, but the spine has to resist twisting from people stepping on one side of a tread, so it is a designed element.
• Zig-zag or folded plate. The stringer is cut or folded to follow each riser and tread, giving a stepped profile. It suits wood or stone treads that sit on top.
• Floating or cantilevered treads. Treads appear to come straight out of a wall, supported by steel brackets or plates fixed into a structural wall. The wall has to be designed for those point loads; drywall on studs won't do it without hidden steel framing.
• Hanging stairs. Treads hung from rods or flat bar connected to the structure above. Common in feature designs; the supports above have to carry the full stair load.

Wood treads suit the double stringer, zig-zag and mono-stringer types, each with its own way of fixing the tread to the steel.

Steel staircase designs for homes vs commercial and industrial

The same layouts show up everywhere, but the details change with the building:

House stairs within a dwelling unit can use winders and open risers and have more lenient dimensions than stairs in public or commercial buildings. Industrial stairs have their own allowances and also have to satisfy Ontario's workplace regulations. Tread choice follows the setting: wood or stone at home, pans in commercial stairwells, grating in plants and outdoors.

What a steel spiral staircase costs, and why

People ask "how much is a steel spiral staircase" more than any other stair price question. We don't publish prices, but the things that drive the cost are predictable:

• Kit or custom. Kits come in fixed diameters and heights. A custom spiral is made for your exact opening and floor-to-floor height. See steel stair kits vs custom stairs.
• Diameter and height. More treads and a larger diameter mean more steel and more fabrication time.
• Treads. Plain plate, checker plate, grating or steel pans for wood or stone.
• Railing. The curved outer handrail and guard are often as much work as the stair itself.
• Finish. Primer, paint, powder coat or hot-dip galvanizing for exterior spirals.
• Getting it in. Spirals are often delivered in pieces and assembled in place, which affects installation time.

The same logic applies to every type: a straight double-stringer stair is the least work per metre of height, and curves, cantilevers and exposed connections add time.

Getting a steel staircase made

We fabricate custom steel stairs of all these types, with CWB certified welding and shop drawings prepared in-house, and we can prime or galvanize to suit the location. Engineering services are available for stairs that need a designer, such as mono-stringers and cantilevered treads. Installation is by your installer or contractor.

Send us the floor-to-floor height, the opening size, photos and any drawings for a free quote, or see our services for the rest of our miscellaneous steel work.