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2751 Production Way, Burnaby, B.C., V5A 3G7 Double Undermount Stringers
A double undermount stringer configuration places two structural stringers beneath the treads — one under each edge — rather than relying on a single center spine. Like single undermount construction, both stringers stay hidden beneath the treads, so the staircase still reads as a clean, floating structure from above. The difference is in how the load is carried: splitting the support across two stringers shares the weight across two points rather than concentrating it in one, which opens up options for wider treads, longer spans, and heavier-traffic applications. Metal and Wood Products fabricates double undermount stringers in three configurations, each suited to a different combination of span, load, and design intent.
Design Features
Because the load is distributed across two stringers instead of one, double undermount construction trades the pure engineering challenge of single-stringer torsion for a different set of considerations: stringer alignment, tread-to-stringer connection consistency, and matching both stringers precisely so the tread sits level and true across its full width. Metal and Wood Products builds double undermount stringers using three approaches, chosen based on the project’s span, load, and finish requirements.
Tube Style
Made from standard H.S.S. tubing sections, tube stringers are the most straightforward and cost-effective double undermount option. Because two stringers are already sharing the load, standard tube sizing handles most residential spans without requiring a heavier custom profile — a practical choice when budget and lead time matter as much as aesthetics.
Profile Cut Plate Style
Fabricated from steel plate and cut on our waterjet to any profile, plate stringers give double undermount staircases a sharper, more defined edge than tubing allows. Because the profile is cut rather than extruded, plate stringers can be shaped to unusual dimensions or tapered forms — a common choice when the staircase needs to match a specific architectural detail elsewhere in the space.
I-Beam Style
Built from standard structural I-beam sections, or custom-fabricated to mimic the I-beam profile, this configuration delivers the highest load capacity of the three. I-beam stringers are the typical choice for longer spans, commercial applications, or any staircase carrying above-average foot traffic. See our full I-beam stringer page for more on this option.
Structural Performance
Splitting support across two stringers changes the engineering approach compared to a single center stringer. Rather than sizing one profile to resist twisting under the full tread load, a double undermount system is engineered so both stringers deflect evenly and share load in proportion — which means precise fabrication and consistent connection points matter as much as the stringer profile itself. Done well, this produces a rigid, quiet staircase with no perceptible flex, even under heavier commercial loads.
All double undermount staircases are engineered to meet BC Building Code requirements for load capacity, guardrail integration, and tread dimensions, whether under Section 9.8 for private stairs or applicable commercial code provisions for larger projects. Because both stringers are concealed beneath the treads, careful attention to tread attachment and long-term connection integrity is what keeps the staircase performing well years after installation.
Customization Options
Every double undermount staircase is custom-fabricated to the project’s span, tread dimensions, and load requirements. Profile selection — tube, plate, or I-beam — along with stringer size and wall thickness, is calculated based on span, expected traffic, and material choice.
Finish options include powder coating in a wide color range, painted finishes, or raw and clear-coated steel. Tread materials pair well across the full range — hardwood, engineered wood, steel, concrete, or glass — and because both stringers stay hidden, railing systems typically mount at the tread edge or wall connection for a clean sightline, similar to single undermount designs but with the added stiffness to support heavier glass or cable railing runs where required.
Ideal Applications
Double undermount stringers are the go-to choice whenever a project calls for a floating staircase appearance but the span, tread width, or expected load exceeds what a single center stringer comfortably handles. This makes them well suited to wider residential staircases, feature stairs in larger open-concept homes, and any space where the staircase needs to carry more than typical foot traffic.
Commercial and multi-family applications benefit especially from the I-beam configuration, where code-driven load requirements and higher usage make the added capacity worthwhile. For residential projects, tube or plate double undermount stringers offer the same floating aesthetic as single undermount construction with extra structural margin — a common upgrade when a client wants a wider staircase without a visible center support.
Frequently Asked Questions
ABOUT OUR DOUBLE UNDERMOUNT STRINGERS
How much do double undermount stringers cost?
Double undermount staircase costs depend on the profile selected (tube, plate, or I-beam), span, finish, and tread material. Tube stringers are typically the most economical, plate stringers sit in the mid-range depending on cut complexity, and I-beam configurations — built for higher load capacity — represent the premium option. Contact our team for a quote based on your project’s specifics.
What's the difference between single and double undermount stringers?
Single undermount stringers use one center stringer beneath the treads, while double undermount stringers use two — one under each edge. The double configuration shares structural load across two support points instead of concentrating it in one, making it a better fit for wider treads, longer spans, or heavier-traffic applications. Both configurations produce the same hidden-support, floating-stair appearance.
Do double undermount stringers work for commercial buildings?
Yes, and they’re often the preferred undermount option for commercial applications specifically because of their higher load capacity. I-beam double undermount stringers in particular are well suited to the traffic volumes and code requirements typical of commercial and multi-family projects.
Can double undermount stringers span wider staircases than single undermount?
Generally, yes. Because two stringers share the load, double undermount construction can support wider treads and longer spans than a single center stringer of comparable size. The exact span capability depends on the profile chosen — tube, plate, or I-beam — and is calculated for each project based on load and dimension requirements.
Do double undermount stairs meet BC Building Code requirements?
Yes. All double undermount staircases we fabricate are engineered to meet BC Building Code requirements — Section 9.8 for private stairs, or the applicable commercial provisions for larger projects — covering load capacity, tread dimensions, and guardrail integration.
Double undermount staircase
Riser tube and glass conection
Next Steps for Your Double Undermount Stair Project
Currently planning a custom build or renovation?
Share your project details, space measurements, and design preferences with our team. We’ll discuss tube, plate, and I-beam stringer options, recommend the right configuration for your span and load requirements, and provide guidance on timeline and budget considerations.
Working with an architect or designer?
We collaborate directly with design professionals throughout the Greater Vancouver area. Request our technical specifications, load capacity data, and profile dimensions to incorporate double undermount stringer systems into your project plans.
Exploring staircase options?
Compare our full range of modern staircase designs, including side stringers, cantilevered stringers, and single undermount configurations. Each offers distinct aesthetic and structural characteristics for contemporary spaces.
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