Guide

Mono stringer staircase installation guide

A well-fabricated mono stringer stair is straightforward to install if the site is ready and the shop drawings match reality. A poorly-coordinated install turns into a week of rework, angry framers, and a stair that bounces because the top connection landed in the wrong beam. This page is the on-site reference for installing a mono stringer stair, the sequencing, substrates, connections, and coordination points we work to on every install out of our Burnaby shop across Metro Vancouver.

The audience for this page is GCs, project managers, and homeowners who want to understand what a mono stringer install involves and how to prepare the site for it. For the engineering behind the stringer itself, see the engineering guide. For the design choices that drive the install detail, see the design guide.

What has to be done before the stair arrives

The installation day starts long before the truck shows up. These items need to be confirmed during framing, concrete, and pre-drywall inspections:

• Rough stair opening framed to the dimensions on the shop drawings, measured at the floor and at the ceiling (openings twist during framing and the top and bottom dimensions can disagree by 20 mm on a framer who isn't paying attention)
• Top connection substrate in place, structural beam, embedded plate, or engineered LVL header, at the elevation specified on the shop drawings
• Bottom connection substrate in place, concrete slab cured to minimum strength, or wood-framed floor with doubled joists and header ready to receive through-bolts
• Any embedded anchors or plates cast into concrete in the correct location with adequate edge distance per the engineer's detail
• Drywall complete in the stair opening area, cut close to but not tight against the planned stringer location
• Finish flooring NOT yet installed in the stair area, the stair goes in before flooring
• Clear path from delivery door to the stair location, wide and tall enough to carry a stringer of the full length (up to 18 ft straight)
• Power available on site for minor field welding or grinding if needed

Opening framing dimensions

The rough opening has to accommodate the full width of the stair assembly including treads, plus clearance for drywall and finish trim. For a typical mono stringer with a 4 inch wide stringer and 12 inch tread overhang each side, the tread-to-tread width is 28 inches and the required opening is 32 inches minimum for finishing clearance.

Length of the opening has to accommodate the stair run plus clearance at top and bottom for connections. For a 14 ft run, we typically ask for a 15 ft clear opening between floor structure above and slab below, with the understanding that the upper floor framing has to pass far enough back to allow the stringer to clear the front edge of the floor.

Specific dimensions come from the shop drawings for every project. We provide those drawings to the GC and the framer during the pre-framing coordination phase, and we do a site walk during framing to catch any discrepancies before they become installation-day problems.

Substrate options for top and bottom connections

The stringer has to anchor into something structural at both ends. The three common substrates in Metro Vancouver residential construction:

• Concrete slab (bottom): A cast-in-place or basement slab, minimum 100 mm thick, cured to 25 MPa. Anchoring uses post-installed wedge anchors or epoxy anchors sized by the engineer. Edge distance has to be enough to develop the anchor, typically 100 mm minimum from the slab edge. Embedded plates cast into the slab are an alternative that allows welded rather than bolted connections.
• LVL header or doubled joists (top): An engineered wood header or doubled solid joist set to carry the top reaction. Connection uses through-bolts with washers, or a steel side plate that the stringer bolts to and the plate attaches to the wood with structural screws. Wood-to-steel connections in seismic zones require careful detailing, the wood has to have enough fibre to develop the bolt without splitting.
• Structural steel beam (top or bottom): A W-shape or HSS steel beam in the floor or ceiling. Welded connection is common and straightforward if the beam is accessible. Bolted connection uses a bolted plate-to-beam shear connection.

Crane vs hand-set decision

How the stringer gets into the building is determined during shop drawings. Key factors: stringer weight, access path width and height, ceiling clearance during the lift, and whether windows or doorways allow the stringer to pass at the correct angle.

Hand-set works for most residential mono stringer stairs. A 14 ft stringer weighing 600 lbs can be carried by four people with proper lifting straps and tilted through a standard doorway. The method is slower and more careful than a crane but avoids the crane truck cost and scheduling.

Crane-set is required for: any stringer over roughly 1200 lbs, stringers that cannot fit through the doorways (too long to turn corners or too wide), and sites with tight access where a hand-set would risk damaging finished surfaces. Crane installs add a half day of GC coordination, crane truck access, sidewalk or road closure permits if needed, and a rigging plan. We coordinate all of that with the GC during the install scheduling phase.

Mechanical hoist is a middle ground, a chain hoist or lever hoist anchored to the building structure can lift a heavy stringer vertically inside the house without needing a crane. Useful for stairs going up a stairwell where a crane cannot reach.

Bottom connection mechanics

The bottom of the stringer usually lands on a concrete slab. The base plate, welded to the bottom of the stringer in the shop, is lined up with the layout marks on the slab and the anchors are installed through the base plate into the slab.

Anchor sequencing matters: for epoxy anchors, the holes are drilled and cleaned, epoxy is injected, and the anchor rod is inserted and held in place until cure. For wedge anchors, the holes are drilled, the anchors are inserted through the plate and into the concrete, and a hammer impact drives the wedge. Either way, the anchors get torqued to the engineer's spec before the stringer is loaded.

If the base plate does not sit flush because the slab is not perfectly flat, non-shrink grout goes under the plate before the anchors are final-torqued. Grouting the base plate is the standard detail and happens on almost every install where the slab is more than a few millimetres out.

Top connection mechanics

The top of the stringer connects to whatever is above, a steel beam, an embedded plate, or a wood header. The detail is a steel plate welded to the top of the stringer in the shop, which bolts or welds to the receiving structure on site.

For a bolted connection, the receiving plate has pre-drilled holes matching the stringer end plate. The stringer is lifted into position and the bolts thread through from the stringer side into tapped holes or through with nuts on the back side. Torque happens with a calibrated torque wrench and the values are recorded.

For a welded connection, the stringer is tack-welded in position, plumb and elevation are verified, and the final welds are run by a welder qualified under CSA W47.1. All field welds are inspected visually and, if the engineer requires, with ultrasonic or magnetic particle testing.

Tread installation sequence

With the stringer locked in, treads go on from bottom to top. Each tread has a bracket on the stringer and bolts or drops onto that bracket per the shop detail. Typical hardware is 1/4 inch or 5/16 inch socket-head cap screws threaded up from underneath into tapped holes in the tread backing. For hardwood treads, the tapped holes are in a steel plate let into the underside of the tread during tread fabrication, not into the wood itself.

Each tread is set level with a spirit level before the next one goes in. A shim pack of thin steel plates is available to correct any minor bracket deviation. The treads are verified plumb to the stringer centreline to keep the overall stair straight.

Wood treads typically ship separately and install after the stringer is powder-coated and set. This minimizes finish damage during fabrication and shipping. Steel treads may ship pre-attached if they are welded to the stringer, in that case the whole assembly is shipped as one piece.

Guard, handrail, and finishing

After the treads are in, the guard system goes on: guard posts or newels anchored to the tread or the stringer, balusters or glass panels between posts, top rail across the posts, and handrail along the top rail or wall-mounted bracket. Every connection is verified against the shop drawings and every code dimension is verified on site: handrail height, guard height, sphere test on the guard, handrail returns at both ends.

Wall-mounted handrails anchor into wall blocking that was installed during framing. If the blocking is missing, it happens, we drill and install toggle bolts or wall anchors sized for the handrail load (0.9 kN at any point per BC Building Code), and flag the issue to the GC for proper repair before final sign-off.

Final QC

Every mono stringer install ends with a QC checklist that we walk through with the GC or the homeowner:

• Every bolt torqued to spec, torque values recorded where the engineer required it
• Every tread level within ±1 mm side-to-side and front-to-back
• Every tread secure with no movement under a 90 kg load test
• Handrail continuous with compliant returns at both ends
• Guard at compliant height with no opening passing the 100 mm sphere test
• No visible damage to the powder coat or tread finish
• Site protection in place on treads and handrail
• Touch-up paint left behind for the GC

Site protection during the rest of the build

After install, other trades still need to work in the house, flooring, tile, paint, millwork, and every one of them can damage a freshly installed stair. We cover the treads with ram board or corrugated plastic and tape protective film to the handrail and stringer edges before we leave. The GC takes over from there. For paint touch-ups during the build, we leave behind colour-matched touch-up in small containers.

Major damage after install, deep scratches through powder coat, bent hardware, cracked glass panels, requires a return visit for repair. We track any damage reports and schedule a repair visit before the final walkthrough.

Seismic inspection and sign-off

On commercial and larger residential projects, the structural engineer of record typically wants a visual inspection of the stair connections before the stair is considered complete. We coordinate that inspection at a time when all connections are accessible, before the drywall finisher wraps the last of the stringer, or with a specific inspection access panel built into the detail. The engineer signs off on the connection installation and issues the field review letter required for the occupancy permit.

Related reading

For the engineering behind the install details, see the engineering guide. For the design choices that shape the install, see the design guide. For cost by component, see the stair cost guide. For a project-specific quote, request a quote.

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