Steel Stairs with Wood Treads: Design Guide

A steel stair with wood treads uses steel stringers or a steel spine to carry the load and solid wood treads to give a warm, quiet walking surface. The treads usually sit on steel angles, plates or pans welded to the stringers and are fastened from underneath, out of sight. Under the 2024 Ontario Building Code, wood treads in a dwelling unit must be at least 25 mm thick, or 38 mm where risers are open and the stringers are more than 750 mm apart, and the tread finish must be hardwood, vertical grain softwood, resilient flooring or an equivalent.

It's the most popular custom stair in Ontario homes for good reason. This guide covers the design decisions that make one look right, meet code and stay quiet for years. If you're still deciding between materials, start with steel stairs vs wood stairs.

Steel frame options

The frame sets the look and decides how the treads are supported.

Side stringers are the simplest and stiffest. Mono stringers and floating treads look lighter but put the tread in a cantilever, so the steel brackets, the tread thickness and the anchorage all need a designer's attention. Wall-supported treads need solid backing in the wall, which has to be planned before drywall. For stringer sections and sizing, see steel stair stringer sizes.

How the wood treads attach

The tread-to-steel connection is where most problems start, so it's worth getting right on the shop drawings.

• Support under the tread. Angles, flat plates or pans give the tread a bearing surface. The longer the support, the less the tread has to span on its own.
• Fasten from below. Screws go up through holes in the steel into the tread so nothing shows on top. The screws must be short enough not to come through the tread.
• Slotted holes. Wood expands and shrinks across its width with humidity. Slotting the holes in the steel lets the tread move without splitting or loosening.
• Isolation pads. A thin rubber or neoprene pad between the steel and the wood stops the squeak and click of wood moving on metal.
• Set the nosing. Decide how far the tread overhangs the steel at the front. The code limits how far a tread's depth can exceed its run, which controls the nosing projection.

Hole positions on the steel have to match the treads, so the steel fabricator and the tread maker need to work from the same dimensions. It's common for the steel to be built and installed first and the treads measured from the finished frame.

Code points that affect wood treads

The general stair rules for rise, run, width, headroom, landings, handrails and guards apply to every stair. They're covered in our guide to Ontario Building Code rules for steel stairs. These are the ones that bear most directly on wood treads:

Two practical notes. First, the thickness minimum is a floor, not a design: a 38 mm tread spanning between close stringers is very different from the same tread cantilevering off a mono stringer, and the designer sets thickness for the actual support. Second, the nosing rule means a sharp square edge on a hardwood tread isn't acceptable; specify the bevel or radius with the treads.

Choosing the wood

Most interior treads are solid hardwood such as oak, maple or walnut, either one piece or edge-glued. Points to consider:

• Stability. Wide, flat-sawn boards move more and cup more. Edge-glued or quarter-sawn stock is more stable.
• Moisture content. Treads should be dried and left to acclimatize to the house before they're installed, especially in a new build where the house itself is still drying out.
• Finish all six sides. Sealing the underside and ends as well as the top slows moisture exchange and reduces cupping.
• Thickness for the span. The heavier the use and the longer the unsupported span, the thicker the tread.

Exterior steel stairs with wood treads

Steel frames with wood treads are also used outdoors on decks and entries, with different priorities:

• Durable species or treated wood. Exterior treads need wood that tolerates wetting, and drainage gaps between boards if the tread is made up of planks.
• Galvanized or well-coated steel. Exterior steel needs corrosion protection, and water must not be trapped between wood and steel.
• Slip resistance. Wet wood is slippery; grooved or textured surfaces help.
• Fasteners. Use corrosion-resistant fasteners compatible with the steel coating and the wood.

Our post on exterior steel stairs covers outdoor frames in more detail.

Planning the job

A steel and wood stair involves at least two trades, sometimes three, so sequence matters:

1. Design and measurement. Floor-to-floor height, opening size, stair type and tread layout are set first. A designer or engineer details the steel where the design goes beyond a simple stair.
2. Shop drawings. The steel is detailed with tread supports and hole positions; the dimensions are shared with the tread maker.
3. Steel fabrication and finish. Paint or powder coat is applied before the stair goes in.
4. Steel installation. The frame is set, levelled and anchored.
5. Treads. Measured from the installed frame, finished and fastened from below with isolation pads.
6. Guards and handrails. Usually steel, sometimes with glass or wood rails. See steel stair railings and handrails.

Steel stair frames made to your design

We fabricate custom steel stairs, railings and miscellaneous steel to suit your project, with shop drawings prepared in-house and CWB certified shop welding. Send us your drawings or the floor-to-floor height, stair width and style you want and we'll quote the steel. We fabricate and deliver, and installation is by your installer or contractor. See our services for how a stair goes from drawings to delivery.