Mono Stringer Staircase Fabrication in Southern Maine

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Floating Staircases Portland, Maine: Custom Steel Staircase Fabrication

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NRK Welding designs and fabricates custom mono stringer staircases for residential and commercial projects throughout Southern Maine. Call (207) 899-6084 for a free quote. Most estimates are returned within 24–48 hours.


A mono stringer staircase uses a single central steel spine to support cantilevered treads on both sides. It is one of the most structurally demanding and visually open staircase designs available. If you know what you want and need a fabricator with the precision to build it correctly, contact NRK Welding to get started.

What Is a Mono Stringer Staircase?

A mono stringer staircase (also called a single stair stringer, mono stair stringer, or single beam staircase) runs a single continuous steel spine up the center of the structure. Each tread is welded or bolted to the spine and cantilevers outward on both sides, with no lateral support visible from the sides or below. The result: a sequence of treads that appear to float with nothing supporting them.


The structural logic is concentrated rather than distributed. All torsional and shear load resolves through one heavily engineered central member, typically a rectangular hollow section (RHS) or wide-flange beam, selected for span, load, and cantilever distance. When engineered correctly, a mono stringer steel staircase meets the same structural ratings as a conventional two-stringer design while delivering a far more open visual profile.


This is a technically demanding build. Buyers searching for a mono stringer staircase fabricator already know what they want. NRK Welding builds to that standard: every mono stringer we fabricate is engineered for load, deflection, and vibration, and not just appearance. We handle the full process in-house: site measure, CAD design, steel fabrication at our Saco, Maine shop, and on-site installation.


Mono Stringer vs. Dual Stringer Staircases

Mono Stringer Double Stringer
Load path Single central spine Two parallel side beams
Tread support Cantilevered from center Spans between side stringers
Visual profile Fully open: sides and underside are clear Enclosed: side stringers are visible
Best application Open-plan residential, commercial lobbies, feature staircases Traditional interiors, high-traffic commercial, wall-integrated designs
Space requirement Narrower lateral footprint: spine occupies center only Wider: stringers extend to outer tread edge
Fabrication complexity Higher: tread weld joints carry torsional load Lower: load path is simpler
Relative cost Higher due to engineering and fabrication intensity Lower for equivalent span and load rating

Both types are fully custom-fabricated at NRK Welding. Both carry a lifetime structural warranty. If you're deciding between the two for a specific project, call us, and we'll walk through the structural and cost implications for your exact site conditions.


NRK Welding also fabricates floating staircases and the full range of custom steel staircases. Mono stringer design is a structural sub-type of the floating stair family — if you've seen a floating staircase you liked, there's a good chance it was mono stringer construction.



Steel Mono Stringer Fabrication Process

Every mono stringer stair NRK Welding builds is engineered and fabricated from scratch for the project. Here's what the process looks like from first contact to final installation.

1. Site Measure & Structural Assessment


We visit the project site, take precise measurements, and assess the substrate at both the top and bottom connection points. Floor and ceiling connections carry the full load of the staircase, so these must be evaluated before any design work begins. Our design and engineering process starts here.


2. Spine Engineering & Steel Grade Selection


The spine is the critical member. We select steel grade (typically A500 structural steel for the spine and A36 for connection plates) based on span length, total live and dead load, and cantilever distance. Standard cantilever distances for mono stringer designs typically run in the 18–22 inch range per side before deflection becomes a governing design constraint. However, the actual limit depends on spine section size, steel grade, total load, and tread spacing specific to each project. Longer cantilevers are achievable with a heavier spine section or reduced tread spacing.


Every tread-to-spine weld joint is engineered for both vertical shear load and the torsional moment introduced by cantilevered load distribution.


3. In-Shop Fabrication


All fabrication takes place in our Saco, Maine facility. Spine sections are cut, prepped, and welded using MIG and TIG processes, depending on joint type and specification. Tread connection plates are welded to the spine at precise angles to hold a consistent rise and run across the full flight. Sub-assemblies are test-fitted in the shop before delivery. Tolerance control at this stage is non-negotiable, as inconsistent tread angles become visible immediately on installation.

4. Surface Finishing


Finishing options include powder coat (most durable; available in any RAL color), direct-to-metal paint for custom colors, or mill finish for a raw industrial aesthetic that develops patina over time. We sandblast before all painted and powder-coated finishes to ensure adhesion. Handrail anchors and tread mounting hardware are finished to match the spine.

5. On-Site Installation


The spine is anchored at the base plate and upper landing plate using structural fasteners suited to the substrate, such as concrete, steel, or timber framing. Treads are fitted and final-torqued on-site. Handrails and balustrades are installed last. Every tread is checked for level and every connection for movement before sign-off.

Call Us to Get a Fabrication Quote for Your Project

Our Meticulous Fabrication Process

Our process is built on precision and collaboration. From the initial design to the final weld, we manage every detail to ensure the highest quality.


  • Conceptual Design: We start by discussing your vision, taking measurements, and reviewing architectural plans.
  • Engineering & Blueprinting: Our team engineers a detailed blueprint that adheres to all structural requirements and building codes.
  • In-Shop Fabrication: Using state-of-the-art equipment in our Saco, Maine facility, our certified welders expertly fabricate the staircase components.
  • On-Site Installation: Our professional installers handle the final installation with care and precision, ensuring a perfect fit and finish.


View Our Custom Steel Staircase Portfolio

Mono Stringer Staircase Applications

The mono stringer steel staircase performs best in projects where visual openness is a design priority, and the staircase is meant to be seen, not just used.


  • Open-plan residential homes. New construction and renovation projects where the staircase is the focal point of the interior. Mono stringer stairs are especially effective in spaces with high ceilings: the single spine reads as a sculptural element. Common in lakefront homes, coastal builds, and contemporary residential projects throughout Cumberland and York Counties.


  • Commercial lobbies and showrooms. High-end retail, architecture offices, and hospitality spaces use mono stringer staircases to create a first impression. The floating tread effect signals quality and design intentionality on arrival. NRK Welding has worked with commercial clients in Portland and across Southern Maine on feature staircases for multi-story lobby environments.


  • Mezzanine access. Mono stringer stairs work well for mezzanine access in converted industrial spaces, breweries, and live-work lofts where floor space is limited. The central spine format allows the staircase to occupy a minimal footprint while maintaining a full-width tread.


  • High-end residential fitouts. Interior designers and architects specify mono stringer designs for custom homes where the staircase is a named element in the project, typically paired with cable railing, glass balustrade, or solid hardwood treads. These projects carry the tightest tolerances and highest visibility.

Tread & Railing Options for Mono Stringer Stairs

The structural spine is fixed by engineering. Tread material and railing system are where the aesthetic direction is set, and both choices need to be locked in before fabrication begins, since railing anchor points are built into the spine.


Tread materials:


  • Solid hardwood: warmth and contrast against steel; most popular for residential applications
  • Steel plate: fully industrial or monolithic look; no material transition between tread and spine
  • Tempered glass: maximum light transmission; most visually open option available


Tread material selection doesn't affect structural performance. The spine carries the load regardless of what sits on top. It's an aesthetic and maintenance decision.


Railing systems:


  • Cable railing installation: open, coastal-contemporary; post spacing and tension load calculations are integrated into the original fabrication design
  • Rod railing: geometric, modern; pairs well with a powder-coated spine
  • Glass balustrade: fully transparent enclosure; requires specific base channel profiles built into the tread structure
  • Custom handrails: wall-mounted or post-mounted; fabricated to match spine finish


Railing system selection affects anchor point engineering. We integrate the railing system into the original fabrication design — not as an add-on after the spine is built. If you have a specific railing in mind, tell us at the outset.


Why Choose NRK Welding for Your Mono Stringer Stairs


  • Full in-house capability: design, engineering, fabrication, and installation handled by one team in Saco, Maine

  • Lifetime structural warranty on every staircase we build

  • Precise tolerance control: mono stringer fabrication requires it; we don't outsource quality checks

  • Local knowledge: we understand Maine building codes, substrate conditions, and the lead times that matter to contractors and homeowners

  • Free quotes: most returned within 24–48 hours after project review

- Bryan Souza

These guys are great. I couldn't be more happier with the service.

- Ryan Santoro

Nick was great at communicating the needs of the project and got it done in a reasonable time frame. I would definitely hire again.

- Jackson Mohr

Fantastic quality. Under the estimate provided and complete ahead of schedule. Cannot recommend Nick enough.

Frequently Asked Questions about Mono Stringer Staircases

  • What is a mono stringer staircase?

    A mono stringer staircase uses a single central steel spine running up the middle of the staircase. Treads are welded or bolted to each side of the spine and cantilever outward, creating the impression that the treads are floating in space with no visible side support. The terms "mono stringer," "single stringer staircase," and "single beam staircase" all describe this same structural configuration.


  • How does a mono stringer staircase differ from a standard staircase?

    A standard staircase uses two side stringers (one on each side) with treads spanning between them. A mono stringer uses one central beam instead. This gives a more open, architectural appearance and allows light to pass freely beneath and around each tread. The trade-off is that a mono stringer requires more precise engineering to achieve the same structural load rating, because all torsional and shear forces resolve through a single member rather than two. For a full overview of the staircase types we build, see our custom steel staircases page.

  • Can NRK Welding fabricate a mono stringer staircase for my home?

    Yes. We fabricate mono stringer staircases for residential homes throughout Southern Maine. We handle the full process: site measure, CAD design, steel fabrication, and installation. Contact us for a free consultation — most quotes are provided within 24–48 hours of project review.


  • What tread materials work with mono stringer designs?

    The most common options are solid hardwood for warmth and contrast, steel plate for a fully industrial look, and tempered glass for maximum light transmission. Tread material doesn't affect structural performance. It's an aesthetic decision based on your space and how the staircase will be used day-to-day. For railing options that pair with each tread type, see our custom handrails page, or speak with our design and engineering team about what works best for your project.

  • How much does a mono stringer staircase cost?

    Mono stringer staircases are custom-engineered projects, so cost varies significantly based on flight length, tread width, tread material, railing system, and finish. They typically cost more than a double-stringer design of equivalent size due to higher fabrication complexity. The spine engineering, tread weld joint tolerances, and connection point detailing all require more time than a standard two-stringer build. NRK Welding provides free, detailed quotes after an initial project review. Contact us at (207) 899-6084 or request a quote online. Most quotes are returned within 24–48 hours.

Get a Quote for Your Mono Stringer Staircase

NRK Welding serves homeowners, architects, designers, and contractors throughout Southern Maine, including Portland, South Portland, Scarborough, Saco, Biddeford, Kennebunk, and Old Orchard Beach. If you're searching for mono stringer stairs in Maine and need a fabricator who handles the full scope in-house, we're the local team to call.



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