How to Build and Install Stairs: Complete Guide for DIYers

Building a staircase is one of the most technically demanding tasks in residential carpentry — and one of the most rewarding when done well. Unlike most framing work, stairs require precise calculation before a single board is cut. An error of 1/4 inch in riser height, repeated across 14 steps, results in a staircase that feels wrong to climb and may fail a code inspection.

This guide walks through the entire process: terminology, code requirements, calculating your specific stair geometry, cutting stringers, installing treads and risers, and hanging the handrail. Work through each step in order, and your stairs will be solid, safe, and code-compliant.

Stair Terminology

Before you calculate or cut anything, get the vocabulary straight. Every term in stair building has a precise meaning.

Rise: The vertical height of a single step — measured from the top of one tread to the top of the next.
Run: The horizontal depth of a single step — the distance from the face of one riser to the face of the next.
Total rise: The total vertical distance from finished floor to finished floor (or ground to landing). This is your starting measurement.
Total run: The total horizontal distance the staircase covers, calculated from the number of treads and the individual run dimension.
Stringer: The angled structural member that supports the treads and risers on each side (and center) of the staircase. Typically cut from a 2x12.
Tread: The horizontal surface you step on. Often 5/4x12 or 2x12 dimensional lumber, or a dedicated stair tread board.
Riser: The vertical board between treads (not always present — open-riser stairs omit them). Typically 3/4-inch plywood or solid lumber.
Nosing: The portion of the tread that overhangs the riser below. Building code requires a minimum nosing on certain stair types.
Headroom: The vertical clearance measured from the front of a tread to the ceiling or obstruction above. Minimum 6 feet 8 inches per most codes.
Newel post: The large structural post at the top and bottom of the handrail.
Baluster: The vertical spindles between the handrail and the tread or bottom rail.

Building Code Basics

Stairs are heavily regulated because poorly designed stairs cause injuries. While codes vary by jurisdiction (always verify with your local building department), the International Residential Code (IRC) sets these common requirements:

Requirement	IRC Standard
Maximum riser height	7-3/4 inches
Minimum tread depth (run)	10 inches
Minimum stair width	36 inches
Minimum headroom	6 feet 8 inches
Handrail height	34–38 inches above tread nosing
Handrail graspability	Must be graspable — round profile 1-1/4” to 2” diameter, or specific graspable profiles for other shapes
Baluster spacing	Maximum 4-inch gap (a 4-inch sphere must not pass through)
Riser height consistency	No more than 3/8-inch variation between any two risers in a flight

The riser height consistency rule is worth emphasizing: every riser must be within 3/8 inch of every other riser. Uneven risers cause stumbles because the body learns the rhythm of a staircase and then is thrown off by an unexpected change. This is why your calculations matter so much.

Calculating Your Staircase: Step by Step

The math for stairs is straightforward once you work through it systematically. Do not skip any steps.

Step 1: Measure the Total Rise

Measure the exact vertical distance from the top of the lower finished floor to the top of the upper finished floor. Use a level and a long straight board if necessary to project the lower floor level to a point below the upper floor. Measure from there up to the upper floor surface.

Example: Total rise = 108 inches (9 feet)

Step 2: Determine the Number of Risers

Divide the total rise by your target riser height (shoot for 7 to 7-1/2 inches initially). Round to the nearest whole number — you cannot have a fraction of a step.

108 ÷ 7.5 = 14.4 → Round to 14 risers

Note: the number of treads is always one less than the number of risers (the top landing serves as the final “tread”).

Step 3: Calculate the Exact Riser Height

Divide the total rise by the number of risers to find your exact riser dimension.

108 ÷ 14 = 7.714 inches, or approximately 7-11/16 inches

This is your riser height. Every riser will be cut to this exact dimension. Even small errors will compound across 14 risers, so be precise.

Step 4: Set the Run

Tread depth (run) is typically set at 10 to 11 inches for residential stairs. A 10-inch run is the code minimum. An 11-inch run is more comfortable and worth using if your floor plan allows the additional horizontal space.

Run = 10.5 inches (example)

Step 5: Verify with Blondel’s Formula

Blondel’s formula is the traditional check for comfortable stair geometry: 2R + T should equal 24 to 25 inches, where R is the rise and T is the run.

2 × 7.714 + 10.5 = 15.428 + 10.5 = 25.93 inches

Close enough — this stair will be comfortable to climb. If your result is significantly outside 24–25 inches, adjust your riser height or run until the formula is satisfied.

Step 6: Calculate the Total Run

Multiply the run by the number of treads (risers minus 1).

13 treads × 10.5 inches = 136.5 inches (11 feet, 4.5 inches) of horizontal floor space required

Verify that this horizontal distance is available in your floor plan. If not, adjust the run dimension or consider an L-shaped or switchback stair design.

Stringer Layout

The stringer is the backbone of the staircase. Accurate stringer layout is the most critical skill in stair building.

Tools Needed

Framing square — the essential tool for stringer layout
Stair gauges (stair buttons) — small clamps that attach to the framing square arms and let you register the square consistently at exactly your rise and run dimensions for each step. A quality framing square with stair gauges makes this job significantly faster and more accurate.
Pencil, tape measure, circular saw, handsaw

Marking the Stringer

Start with a straight, dry 2x12 that is long enough for your stair run plus some extra for the top and bottom connection points.
Set your stair gauges on the framing square: one gauge at the rise measurement on the tongue (short arm), one gauge at the run measurement on the blade (long arm).
Place the square at one end of the 2x12 with both gauges against the top edge of the board.
Mark along the tongue (rise line) and along the blade (run line). This is your first step.
Slide the square along so the gauge on the blade aligns with the end of the previous run mark. Mark again. Repeat for each step.
At the bottom, you will need to subtract one tread thickness from the first riser to keep all risers equal. If your treads are 1.5 inches thick (2x material), the first riser from the floor is 7.714 - 1.5 = 6.214 inches instead of the full 7.714 inches. This accounts for the thickness of the treads sitting on top of the stringers. Without this adjustment, the bottom step will be taller than all the rest.
At the top, mark the plumb cut (vertical line) where the stringer meets the upper landing or header.
At the bottom, mark the seat cut (horizontal line) where the stringer sits on the floor or on a pressure-treated 2x4 ledger at the base.

After marking, double-check: count your rise lines (should equal your number of risers) and your run lines (should equal your number of treads).

Cutting the Stringers

Circular Saw to the Corner

Use a circular saw to make the cut along each rise and run line. Stop the circular saw blade just before it reaches the corner where the rise line meets the run line — do not cut past the corner. Overcutting weakens the stringer significantly at every notch corner, reducing its structural capacity.

Finish with a Handsaw

After the circular saw, use a handsaw or jigsaw to finish each corner cut. The extra two minutes per notch is worth the structural integrity it preserves.

Three Stringers for Wide Stairs

For stairs 36 inches wide or wider, three stringers are required. Two outer stringers and one center stringer. The center stringer prevents tread deflection underfoot, which both feels better and is safer. For stairs wider than 48 inches, engineering or additional stringers may be needed — consult your local code.

Test Fit Before Installing

Before fastening anything, hold the stringers in position (you may need a helper) and check:

Treads will be level when installed
The top of the stringer connects properly to the upper structure
The bottom of the stringer sits flat on the floor
The stringer is plumb on its face

Adjust cuts as needed before committing.

Tread and Riser Installation

Attaching Stringers to the Structure

Stringers can be attached to the upper landing in several ways:

Hanger method: A metal joist hanger or LVL hanger supports the top of the stringer from a header.
Ledger method: A horizontal ledger board is fastened to the header, and the stringer sits on top of it.
Notch method: The stringer is notched to sit against a structural ledger. This method reduces the structural depth of the stringer and is now less preferred.

At the bottom, fasten the stringer to the floor using angle brackets or by bolting through a pressure-treated 2x4 kick plate.

Open Stringers vs. Dadoed vs. Cleat-Supported

Open (cut) stringers: The notched stringer is exposed, and treads simply rest on the horizontal cuts. Simple, traditional.
Dadoed stringers: Grooves routed into the stringer receive the treads and risers, keeping the outside face of the stringer solid. More labor-intensive but more refined appearance.
Cleat-supported: Blocks or cleats are screwed to the stringer to support the treads. Good for retrofit applications.

Installing Risers First

When installing closed-riser stairs (with riser boards), install the risers before the treads. Start from the bottom and work up:

Cut each riser board to the exact width of the stair opening.
Fasten the riser to the framing with construction adhesive and finish nails or screws.
The riser should be flush with the front edge of the stringer notch.

Installing Treads

Cut treads to length — typically the stair width plus any nosing overhang on the exposed side(s).
Nosing overhang (the amount the tread overhangs the riser below) should be 3/4 inch to 1-1/4 inch per IRC code for stairs with risers. Consistent overhang is visually important.
Apply a bead of construction adhesive to the top of each riser and the horizontal stringer cut before setting the tread.
Fasten treads with 2-1/2 inch or 3-inch screws driven at an angle through the back of the tread into the riser, and through the top of the tread into the stringer. Drive screws from the back edge of the tread to avoid visible fasteners on the nose.
Plug any exposed screw holes if using a clear or natural finish.

Pro tip: Use a brad nailer to tack treads in position before driving screws. This prevents the tread from shifting while you fasten.

Handrail and Baluster Installation

Newel Post Location and Fastening

Newel posts are the primary structural element of the railing system. They must be solidly fastened — any wobble in a newel post creates a railing that feels unsafe (and may be unsafe).

Bottom newel: Bolted through the stringer and/or floor structure with a long through-bolt. Surface-mounted newel posts are adequate only with proper fastening to framing.
Top newel: Bolted to the upper landing framing.
Test every newel by applying lateral pressure. There should be no perceptible movement.

Baluster Spacing

The IRC requires that a 4-inch sphere cannot pass through any opening in the baluster system. In practice, this means balusters are spaced no more than 4 inches on center (measuring between baluster faces). Layout your balusters from the center of each tread and space evenly, keeping all gaps under 4 inches.

Balusters on an angled rail are typically cut at the rail angle at the top (or fit into an angled shoe at the bottom). A compound miter saw set to the stair angle makes this cut cleanly.

Handrail Height and Code Requirements

The top of the handrail must be between 34 and 38 inches above the tread nosing, measured vertically. Measure from multiple tread nosings to ensure the rail is consistently at the right height along its full length.

The handrail must be graspable — a person must be able to wrap their hand around it for support. A round rail 1-1/4 to 2 inches in diameter satisfies this requirement. Flat 2x4 rails do not. If you prefer a 2x4 rail for aesthetics, add a graspable handrail on the wall side.

Wall-mounted handrails require 1-1/2 inch minimum clearance between the rail and the wall — room to slide your hand along without obstruction.

Exterior Stairs: Additional Considerations

Exterior stairs face challenges that interior stairs do not: moisture, freeze-thaw cycling, and drainage.

Materials

All structural lumber (stringers, posts) must be pressure treated rated for ground contact (UC4B) at the base and for above-ground use (UC3B) for above-grade framing.
Treads can be pressure-treated 2x12, composite decking material (low maintenance, slip-resistant options available), or hardwood (ipe, tigerwood) for premium applications.
Non-slip tread strips are worth adding to outdoor stairs, especially on smooth wood surfaces that become slippery when wet.

Concrete Pad at the Base

Exterior stair stringers should land on a concrete pad, not on soil or gravel. Without a pad, stringers sink and shift, creating uneven risers over time. The pad also keeps wood off the ground, reducing rot risk. The pad should be below the frost line in cold climates to prevent frost heaving from shifting it.

Drainage

Design the concrete pad with a slight slope away from the structure. Design treads with a 1/8-inch-per-foot slope toward the front edge to shed water. Standing water on stair treads leads to rot, mold, and ice hazards in winter.

Final Inspection Checklist

Before considering the staircase complete, verify:

A well-built staircase is one of the most satisfying projects in carpentry. The geometry is precise, the joinery is structural, and the finished result is something every person in the house uses every day. Work through the calculations carefully, check your work twice before cutting, and the build will go smoothly.