Metal vs Wood Stair Stringers: Cost and Strength Compared

Every staircase hangs on its stringers. These diagonal members carry every tread, riser, footstep, transferring the full load to the floor and the landing.

The two main choices are wood and metal. Wood stringers, usually cut from 2x12 lumber, are the residential default: affordable, easy to cut on site, and familiar to every carpenter. Metal stringers, usually steel plate or channel cut into a zigzag profile or built as a single central spine, cost more up front but span farther, resist rot and insects, and suit modern open-riser designs.

This guide compares the two: how each type works, strength and span numbers, installed costs, durability, and which fits your project. If you are still sizing the stair itself, run the numbers first with the stair stringer calculator.

What a Stair Stringer Actually Does

A stringer is the inclined structural backbone of a staircase. Treads rest on it or between a pair of them, and it carries the combined weight of the stair plus everyone walking on it down to the bearing points at top and bottom.

There are three common profiles. A cut stringer (sawtooth or open stringer) has triangular notches sawn out so treads sit on the steps, with the profile visible from the side. A housed or closed stringer is a solid board with routed grooves that tread and riser ends slot into. A mono-stringer is a single steel spine down the center, with treads cantilevering off each side.

IRC R311.7 governs residential stair geometry (maximum 7.75-inch riser, minimum 10-inch tread depth), and the stringers behind it must safely carry the design loads. A typical 36-inch-wide residential stair uses three stringers spaced 16 to 24 inches apart.

Wood Stringers: The Familiar Workhorse

Wood is what most residential stairs are framed with. A carpenter lays out a cut stringer with a framing square, cuts the notches, and has a pair installed in an afternoon.

The standard material is 2x12 lumber (actual 1.5 by 11.25 inches), usually Douglas fir-larch or southern yellow pine indoors. Outdoors, use pressure-treated lumber rated for the exposure: UC3B above ground, UC4A near or in ground contact. The layout process is covered in our guide to laying out and cutting a stair stringer with a framing square.

Cutting notches removes material, so keep at least 3.5 inches of solid wood at the narrowest point of the cut (the throat). Span is the bigger limit: a 2x12 SPF cut stringer at 16-inch spacing handles an unsupported run of roughly 6 to 7 feet on a standard 7/11 stair. Beyond that you need an intermediate support post, a landing, or a deeper engineered member.

Wood pros: lowest cost, fastest install, easy to modify on site, warm traditional look. Wood cons: vulnerable to rot, insects, and warping when damp; can squeak as it dries.

Metal Stringers: The Strong Contender

Metal stringers are almost always steel: A steel plate zigzag is laser or plasma cut from plate (commonly 3/8 to 1/2 inch thick) into a sawtooth profile mirroring a wood cut stringer. Steel channel stringers are a pair of C-channels with treads bolted or welded between them. A mono-stringer is a single central spine, often rectangular tube steel, with treads cantilevering to each side for a floating look.

Fabrication happens in a shop: the profile is cut, pieces are welded, and the steel is finished. Interiors usually get powder coating; exteriors get hot-dip galvanizing, sometimes with powder coat over it. Because steel is far stronger per inch than wood, members are much slimmer and spans far longer: a steel plate stringer pair easily runs 12 to 16 feet without intermediate support, and a mono-stringer routinely spans a full flight on its own.

Metal pros: far longer spans, slimmer profile, immune to rot and insects, ideal for open risers and floating treads. Metal cons: higher cost, needs a fabricator and shop drawings, lead times of weeks, cannot be trimmed on site.

Strength Compared: Loads, Spans, and Deflection

Residential stairs are designed for a 40 psf live load (commercial stairs under the IBC use 100 psf plus a 300-pound concentrated load). Deflection is typically limited to span divided by 360, which keeps the stair from feeling bouncy.

In practice the comparison breaks down by span:

• Under 7 feet of run: wood wins on value. Three 2x12 cut stringers at 16-inch spacing carry residential loads with deflection well within limits, and framing goes up in hours.
• 7 to 12 feet: wood needs intermediate support or engineered lumber; steel plate stringers handle it as one span with a fraction of the depth.
• 12 feet and up: steel is the practical choice, spanning full flights that wood cannot without posts breaking up the space.
• Stiffness feel: steel deflects less under the same load, so steel stairs feel more solid, especially on open-riser designs where no riser board adds rigidity.

To check what your stair must carry, run your dimensions through the stair load calculator.

Cost Compared: Materials Plus Installation

Cost is where wood dominates. A pair of cut stringers sawn from off-the-shelf 2x12s costs little more than the lumber plus an hour or two of carpenter time, and many DIYers cut their own. A third center stringer barely moves the budget.

Fabricated steel costs a multiple of that. A pair of plate zigzag stringers typically runs 3 to 5 times the material cost of wood stringers for the same stair, including cutting, welding, and finishing. Installation is quick once the steel arrives, but it cannot be trimmed on site if measurements are off, so field dimensions must be exact.

As rough ranges: framing a straight wood stair flight often lands in the low hundreds for materials plus labor, while a comparable fabricated steel stair structure commonly lands in the low thousands. These are broad ranges, not quotes: steel prices, shop rates, and finishes vary widely by region, so get local numbers before committing. The steel staircase calculator helps you lock down geometry for accurate fabrication quotes.

Durability and Maintenance

Indoors and dry, both materials last decades. Differences show up with moisture, insects, and time.

Wood's enemies are rot, insects, and movement. Even pressure-treated lumber needs periodic resealing outdoors, and cut ends and bolt holes are where water gets in first. Indoors, wood slowly dries and shrinks, the classic source of stair squeaks.

Steel's enemy is corrosion. Indoors with a sound powder-coat finish, a steel stringer is essentially maintenance-free for the life of the building. Outdoors, insist on hot-dip galvanizing under the finish and touch up chips promptly, because rust starts wherever bare steel meets water and air.

Which Stringer Should You Choose?

• Choose wood for a standard straight residential stair, a tight budget, DIY or fast-track framing, or traditional closed-riser looks.
• Choose metal for long spans without intermediate posts, open-riser or floating-tread designs, exterior stairs where rot is the main enemy, or a modern aesthetic where slim structure is part of the look.
• Consider the hybrid: steel stringers with wood treads pair steel's span and slim profile with the warmth and sure footing of wood underfoot.

Frequently Asked Questions

Are metal stair stringers stronger than wood?

Yes. Per inch of material, steel is far stronger and stiffer than wood. Steel stringers span 12 to 16 feet or more versus about 6 to 7 feet for a 2x12 wood cut stringer. Both meet residential code when sized correctly; steel just does it with slimmer members and longer spans.

How far apart should stair stringers be spaced?

For a typical 36-inch-wide residential wood stair, use three stringers spaced about 16 inches apart (never more than 24), so treads do not flex between supports. Steel stringers are usually paired at the stair edges regardless of width, and mono-stringers use one central spine.

Can I use wood stringers for outdoor stairs?

Yes, with pressure-treated lumber rated for the exposure (UC3B minimum above ground, UC4A near or in ground contact). Seal all cut ends and plan on periodic resealing. For the longest outdoor service life with least maintenance, hot-dip galvanized steel stringers are the better bet.

Do steel stair stringers rust?

Bare steel rusts, but finished steel does not under normal conditions. Interior powder-coated stringers are effectively maintenance-free. Exterior steel should be hot-dip galvanized, ideally with powder coat over the galvanizing, with coating chips touched up before rust starts.

How long does installation take for each type?

A carpenter typically cuts and installs wood stringers for a straight flight in half a day to a day. Steel stringers set in hours once delivered, but fabrication lead time is usually 2 to 6 weeks, and field measurements must be exact since steel cannot be trimmed to fit.

Final Word

Wood stringers remain the right answer for most residential stairs: cheap, fast, and plenty strong for typical spans. Metal stringers earn their premium with long spans, slim modern profiles, open risers, or maximum durability outdoors. Match the material to the span, the exposure, and the look.