Stringers, Finished Stairs & Commercial Stair Systems

Stringers, Finished Stairs & Commercial Stair Systems

Quick Answer: Mark cut stringers with a framing square set to unit rise and unit run, step the square down the board, then drop the stringer for tread thickness so risers stay equal. Housed stringers hold treads in grooves instead of open notches. Finished stairs (Module 27405) add finish treads, risers, rails, and balustrades. Commercial stairs may be steel pan or prefab but still demand correct rise/run, landings, and attachments.

This section turns calculated unit rise and run into members you can cut and install. It also bridges rough layout (27110) into finish carpentry (27405) and the commercial systems you will see on larger jobs and on assessment items.

Framing-Square Layout for Cut Stringers

A framing square (steel square) has a long blade and shorter tongue. For stairs:

1. Set stair gauges (clips) on the square so one edge reads the unit rise and the other the unit run.
2. Place the square on the stringer stock (commonly a straight 2×12 free of large knots in the remaining belly of wood).
3. Scribe the rise and run lines for the first notch.
4. Slide the square along the board and repeat for each step until you have the full number of risers/treads.
5. Mark the top and bottom plumb/level cuts where the stringer meets the upper header and lower floor or kick plate.

Crown and stock selection: Sight the stringer stock; keep any crown favorable and avoid placing deep notches where defects weaken the remaining section. After notching, enough solid wood must remain below the notches—overcutting a 2×12 into a skinny zigzag destroys capacity. Wide or heavily loaded stairs need a center stringer or engineered members.

Story pole alternative: Some crews lay out a story pole with equal riser marks for the total rise, then transfer to stringers. The framing-square method remains the classic exam and apprenticeship skill.

Dropping the Stringer (Tread Thickness)

If you cut notches to the full unit rise and then install treads of thickness T on top of the seats, the bottom riser becomes unit rise + T (or the top/bottom relationship shifts) relative to finish floors—creating unequal risers. Dropping the stringer corrects this:

• After laying out the notches, cut off a strip equal to the tread thickness from the bottom of the stringer (or reduce the bottom riser cut by T, depending on teaching method and finish stack-up).
• The goal: once treads of thickness T are installed, every finish riser height equals the calculated unit rise from finish floor to finish floor.

Related finish stack-up issues:

• Upper finish floor thickness vs lower finish floor thickness
• Landing finish vs stair tread finish
• Carpet vs hardwood (different build-ups)

Always design the drop and bearing details around finish elevations, not rough subfloor alone, when finishes differ.

Scenario: Unit rise = 7.5", tread stock = 1" thick. Without drop, the first step up from the finished lower floor onto the first tread can be wrong by about 1". Dropping (or equivalent layout adjustment) restores equality across the flight.

Housed vs Cut Stringers

Open vs closed risers: Independent of stringer type—open-riser designs omit solid riser boards where code allows and opening limits are met. Closed risers enclose the vertical face.

Finish stringer / skirt board: On wall-side stairs, a skirt board covers the joint between treads/risers and the wall. On open sides, a finish stringer or fascia may clad a rough carriage.

Installing Rough Stairs — Sequence Snapshot

1. Verify total rise, unit rise/run, and well opening.
2. Frame landings and stair headers/trimmers in the floor system.
3. Layout and cut stringers (including drop); dry-fit.
4. Attach stringers to upper framing with proper bearing/hangers/fasteners per detail—not toenails alone into a skimpy ledger unless designed.
5. Install temporary or permanent treads for safe access as the job requires.
6. Add center carriage if width/load demands it.
7. Proceed to finish materials when the building is dry and dimensions are locked.

Finished Stairs (Module 27405)

Finished stairs convert a safe rough flight into a durable, code-compliant interior feature.

Materials and Parts

• Finish treads: Hardwood (oak, maple, etc.), prefabricated tread stock, or matching engineered products; return nosings on open ends
• Finish risers: Hardwood, paint-grade, or other specified material; tight joints to treads
• Nosing: Integral or applied; consistent projection
• Newel posts: Anchored to structure (not only to thin finish flooring); receive handrail mortises or hardware
• Balusters: Square, turned, or metal; spaced to pass the sphere test; plumb and evenly spaced
• Handrails: Graspable profile; correct height; returns to wall or newel; secure brackets on wall rails
• Shoe rail / fillet: Optional rails that capture baluster bottoms/tops in some systems

Techniques and Quality

• Dry-fit the entire run of treads and risers before final glue/fasteners.
• Maintain equal reveal and tight miters at returns.
• Fasten from locations that will be hidden or plugged; avoid splitting nosings.
• Scribe skirt boards to treads/risers for a tight wall line.
• Install balustrades so the handrail is continuous and smooth at transitions where required.
• Protect finished treads during the remaining construction with runners or covers.

Exam focus: Sequence and purpose—not brand names. Know that finish thickness affects rough layout, that newels need structural anchorage, and that handrail/guard geometry is part of the finish package, not an afterthought.

Commercial Stair Systems Overview

Commercial projects often leave pure site-built wood stairs for limited areas and use engineered systems for egress cores:

Even when the “stringer” is a steel channel, the carpenter’s responsibilities may include verifying floor openings, setting embeds, installing temporary protection, building formwork for pan fill, or finishing adjacent walls and rails. Rise/run uniformity and headroom still apply.

Attachments: Use specified anchors, weld patterns (by qualified welders), or bolt patterns. Field-cutting primary steel stringers without engineering approval is not acceptable. Shop drawings govern hole locations and connection plates.

Safety During Stair Construction

Incomplete stairs are fall hazards. Use temporary treads, guardrails, or controlled-access plans. Keep openings covered or guarded when work pauses. On commercial sites, incomplete exit stairs interact with overall fall-protection and public-protection rules.

Troubleshooting Table

Putting Modules 27110 and 27405 Together

1. Calculate equal unit rise and legal unit run from total rise.
2. Layout stringers with the square; apply drop.
3. Install rough carriages and temporary walking surfaces.
4. Finish treads, risers, skirts, newels, balusters, and handrails.
5. On commercial jobs, coordinate pan/prefab systems with the same geometric rules and the structural drawings.

Carpenters who own both the math and the layout—and who know how finish and commercial systems attach—cover the Stair Systems domain end to end for training modules and the journey-level assessment.