Stair Building Guide

Complete guide to stair construction covering rise/run calculations, code requirements, stringer layout, handrails, and baluster spacing

Rise/Run Formula & Calculations

Critical Rise/Run Formula

The rise/run relationship determines stair comfort and safety. Too steep is dangerous, too shallow wastes space. The "golden rule" formula creates comfortable, safe stairs.

Golden Rule Formula: 2 × Rise + Run = 24-25 inches (ideal human stride)

Code Requirements & Limits

Measurement	IRC Code Requirement	Recommended Best Practice
Maximum riser height	7-3/4" (7.75")	7" to 7-1/2" (most comfortable)
Minimum tread depth (run)	10" minimum	11" (more comfortable, safer)
Maximum riser variation	3/16" between risers	1/16" or less (prevents tripping)
Minimum headroom	80" (6'8")	84" (7') for comfort
Minimum stair width	36" clear width	42-48" for comfort
Tread nose overhang	3/4" to 1-1/4"	1" to 1-1/8" (standard)

Calculating Number of Risers

Step 1: Measure total rise (floor to floor height)
Step 2: Divide by desired riser height (7" to 7.5")
Step 3: Round to nearest whole number for # of risers
Step 4: Divide total rise by # of risers = actual riser height
Example: 108" total ÷ 7.5" = 14.4, use 14 risers = 7.71" each

Calculating Tread Run

Formula: Run = 25 - (2 × Rise) for comfortable stairs
Example: If rise = 7.5", then run = 25 - 15 = 10"
Check minimum: Ensure run is at least 10" (code)
Total run: (# of risers - 1) × tread run = stair length
Example: 14 risers = 13 treads × 10" = 130" total run

Common Rise/Run Examples

7" rise × 11" run: 2(7) + 11 = 25 (perfect, very comfortable)
7.5" rise × 10" run: 2(7.5) + 10 = 25 (perfect, code minimum run)
7.25" rise × 10.5" run: 2(7.25) + 10.5 = 25 (excellent compromise)
6.5" rise × 12" run: 2(6.5) + 12 = 25 (very gradual, good for elderly)
Avoid: 8" rise × 9" run: 2(8) + 9 = 25 (steep, fails code max rise)

Stringer Layout Using Framing Square

Critical Stringer Layout Concepts

Stringers are the backbone of your staircase. Precise layout using a framing square ensures consistent riser heights and tread depths. Understanding crown, drop, and cutting techniques is essential.

Key: Set framing square to exact rise on tongue (short side) and run on body (long side)

Framing Square Setup

1.Attach stair gauges: Clamp to square at rise and run dimensions
2.Example: 7.5" on tongue (rise), 10" on body (run)
3.Position square: Place on stringer board (2x12 typical)
4.Mark cut lines: Trace both legs of square
5.Slide and repeat: Move square to next step, mark again
6.Continue: Layout all steps (# of risers - 1 treads)

Crown & Drop Adjustments

Crown up: Always install stringer with crown (bow) facing up
Bottom drop: Cut tread thickness off bottom of stringer
Why: Accounts for tread material added on top
Example: For 1" treads, cut 1" off bottom of stringer
Result: All risers same height including first step

Stringer Specifications

Component	Specification	Code/Best Practice
Stringer material	2x12 lumber (typical)	Pressure-treated for exterior
Number of stringers	3 minimum for 36" wide stairs	Add 1 per 16" of additional width
Minimum material left	5" below tread cut (code)	6" preferred for strength
Tread nose overhang	3/4" to 1-1/4"	1" to 1-1/8" standard
Riser boards (closed)	3/4" plywood or 1x pine	Optional for appearance

Cutting Stringers - Pro Tips

• Use circular saw for straight cuts, stop 1/4" before inside corners
• Finish inside corners with jigsaw or hand saw (prevent overcuts)
• Cut first stringer, test fit, then use as template for others
• Check all risers with framing square before cutting remaining stringers
• Sand cuts smooth to prevent splinters and ensure good tread contact
• For long spans, consider LVL or engineered lumber for no-sag performance

Tread & Riser Installation

Critical Consistency Requirement

Building codes mandate that all risers must be within 3/16 inch of each other. Even small variations cause tripping hazards. Consistency is more important than perfection to a target dimension.

Rule: Riser height variation must not exceed 3/16 inch between highest and lowest (1/16" preferred)

Tread Installation

Material: 1" or 1-1/8" hardwood, or 5/4 decking
Width: 10-12" for interior, 11" typical minimum
Overhang: 1" to 1-1/8" beyond riser (tread nose)
Fastening: 3" screws into each stringer (pre-drill hardwood)
Adhesive: Construction adhesive plus screws for squeak-free
Order: Install from bottom up for easier access

Riser Installation (Optional)

Material: 3/4" plywood or 1x6 to 1x8 pine boards
Purpose: Finished look, keeps items from falling through
Install first: Risers go in before treads for clean look
Fastening: 2" screws or nails into stringer edges
Open risers: Legal if openings are 4" or less (code)
Paint/stain: Finish before installation for cleaner result

Tread Nose Options

Bullnose tread: Rounded edge, most comfortable and safe
Square edge: Simple 90-degree edge, modern look
Tread nosing: Separate piece added to edge, replaceable
Return nosing: Nosing wraps around open side for finished appearance
Anti-slip: Rubber, abrasive, or grooved inserts for traction
Carpeted: Pad and carpet over wooden treads for comfort

Handrails & Guard Rails

Code Requirements for Safety

Handrails and guard rails are critical safety features with specific code requirements. These requirements exist to prevent falls and provide support.

Key: Handrail height 34-38 inches, guard rail minimum 36 inches, baluster spacing max 4 inches

Handrail & Guard Rail Requirements

Component	IRC Code Requirement	Notes
Handrail height	34" to 38" above tread nosing	Measured vertically from nose to top of rail
Handrail required when	4 or more risers	One handrail minimum, both sides recommended
Graspable diameter	1-1/4" to 2" (circular)	Must be graspable with 1-1/4" to 2-3/4" perimeter
Guard rail height	36" minimum	For open sides, landings, balconies
Baluster spacing	4" maximum opening	Prevents child's head from fitting through
Handrail clearance	1-1/2" from wall minimum	Allows hand to grip without obstruction
Handrail returns	Required at ends	Return to wall or post, no sharp ends
Load requirement	200 lbs in any direction	Must be solidly attached to structure

Handrail Installation

Height: 36" typical (mid-range of 34-38")
Brackets: Mount every 4 feet maximum
Fastening: 3" screws into studs or blocking
Continuity: Must be continuous from top to bottom
Extensions: Extend 12" beyond top and bottom steps
Material: Wood 2x4, metal pipe, or composite rail

Baluster Spacing Calculation

Maximum gap: 4 inches between any balusters
Formula: (Run length - baluster width) ÷ 4" = # needed
Round up: Always round up for code compliance
Example: 36" run with 1.5" balusters = 9 balusters
Spacing: Divide remaining space evenly between balusters
Testing: 4" sphere should not fit through any opening

Guard Rail & Baluster Options

Wood balusters: Traditional 2x2 or turned spindles, painted or stained
Metal balusters: Iron or steel, various designs, very durable
Cable rail: Stainless steel cables, modern look, unobstructed views
Glass panels: Tempered glass between posts, contemporary style
Composite: Low-maintenance vinyl or composite systems
Building: Solid knee wall with cap rail (36" minimum height)

Step-by-Step Stair Building Process

Calculate Rise, Run & Total Dimensions

•Measure total rise: exact vertical distance from finished floor to finished floor
•Divide by desired riser height (7 to 7.5 inches) to get number of risers
•Round to nearest whole number, then recalculate: total rise ÷ # risers = actual riser
•Calculate run using formula: Run = 25 - (2 × Rise) for comfortable stairs
•Verify run is at least 10 inches (code minimum), 11 inches preferred
•Calculate total run: (number of risers - 1) × tread run = stair length
•Check headroom: minimum 80 inches clearance along entire stair run
•Verify you have space for calculated total run in your floor plan

Select & Prepare Stringer Material

•Choose 2x12 lumber for typical stairs (2x10 for very low rise stairs)
•Use pressure-treated lumber for exterior or basement stairs
•Select boards with minimal crown (bow), avoid large knots in cutting area
•Calculate length needed: use Pythagorean theorem (rise² + run² = stringer length²)
•Allow extra 12 inches on each end for attachment and cutting adjustments
•Purchase 3 stringers minimum for 36-inch wide stairs (4 for 48-inch wide)

Layout First Stringer with Framing Square

•Attach stair gauges to framing square at rise and run dimensions
•Place board with crown facing away from you (crown will face up when installed)
•Start at top of board, position square and mark first step
•Slide square down, keeping gauges tight to board edge, mark each step
•Mark all steps - remember you need (# of risers - 1) tread cuts
•Mark top plumb cut (attaches to upper floor framing)
•Mark bottom level cut (sits on lower floor)
•Measure tread thickness, cut that amount off bottom to account for first tread

Cut First Stringer & Test Fit

•Use circular saw to cut along layout lines
•Stop cuts 1/4 inch before inside corners to avoid over-cutting
•Finish inside corners with jigsaw or hand saw for clean 90-degree cuts
•Cut top plumb cut and bottom level cut (with tread thickness removed)
•Test fit stringer in position, checking rise and run at several points
•Verify bottom sits flat and top attaches at correct height
•Make any needed adjustments before using as template
•Measure each riser height with framing square - should all be identical

Cut Remaining Stringers Using Template

•Use first stringer as template, trace outline onto remaining boards
•Pay attention to crown direction - should face up on all stringers
•Cut remaining stringers following traced lines precisely
•Sand all cuts smooth to remove splinters and ensure good tread contact
•Test fit all stringers - they should be identical
•Number stringers to keep track during installation

Install Stringers & Attach to Structure

•Install outside stringers first, then middle stringer(s)
•Attach top of stringers to upper floor using joist hangers or ledger board
•Use 3-inch structural screws or 16d nails for solid connection
•For bottom, attach to concrete with tapcon screws or use treated bottom plate
•Check each stringer is plumb and level side-to-side
•Ensure all stringers are at exact same height - critical for consistent risers
•Space stringers evenly: outer stringers 1-2 inches from edges, middle evenly spaced
•Add temporary bracing between stringers to prevent movement during construction

Install Risers (If Using Closed Risers)

•Cut riser boards to width (match your calculated riser height)
•Cut to length: stair width minus any overhang for stringers
•Pre-finish risers with paint or stain before installation
•Start from bottom, work up (easier access)
•Apply construction adhesive to stringer edges where riser will attach
•Nail or screw risers to stringer edges with 2-inch fasteners
•Ensure risers are tight to stringer cuts with no gaps
•Fill any gaps with caulk for finished appearance

Install Treads from Bottom to Top

•Cut treads to length: stair width plus any desired overhang on open side
•Cut depth: your calculated run plus nose overhang (typically 11 inches total)
•Apply construction adhesive to top of stringer cuts
•Set first tread, ensuring proper nose overhang (1 to 1-1/8 inches)
•Pre-drill pilot holes in hardwood to prevent splitting
•Drive 3-inch screws through tread into each stringer (2 screws per stringer)
•Continue up stairs, checking each tread is level and overhang is consistent
•Use scrap block under front edge while fastening to prevent tread sagging

Install Handrail Posts & Balusters

•Install newel posts at top and bottom, secured through tread and stringer
•Use 1/2 inch lag bolts or structural screws for solid post attachment
•If required, install intermediate posts (max 6 feet apart)
•Calculate baluster spacing: no more than 4 inches between any balusters
•Cut balusters to length, accounting for angle of stairs
•Install balusters using finish nails or screws from underside of treads
•Ensure balusters are plumb even though stairs are angled
•Use spacer jig to maintain consistent spacing between all balusters

Install Handrail & Final Finishing

•Cut handrail to length with proper angle to follow stair pitch
•Height: 34 to 38 inches above tread nosings (36 inches typical)
•Attach rail to posts with rail bolts or screws
•For wall-mounted rail, install brackets every 4 feet into studs
•Ensure rail is continuous from bottom to top (no breaks)
•Return handrail ends to wall or post - no sharp exposed ends
•Fill all nail holes with wood putty, sand smooth
•Apply final finish: paint, stain, or polyurethane as desired
•Install any trim pieces, skirt boards, or under-stair finishing
•Final inspection: test handrail strength (should support 200 lbs), check all risers are consistent

Best Practices & Common Mistakes

DO:

Calculate rise and run carefully - double-check all math before cutting
Use the 2×Rise + Run = 24-25 formula for comfortable stairs
Cut first stringer and test fit before cutting remaining stringers
Remember to subtract tread thickness from bottom of stringer
Maintain consistent riser heights - variation causes tripping hazards
Install handrails at 34-38 inches and ensure 200 lb load capacity
Keep baluster spacing under 4 inches (4-inch sphere test)
Use construction adhesive plus screws to eliminate squeaks

DON'T:

Exceed 7-3/4 inch maximum riser height (code violation, tripping hazard)
Forget to account for finished floor heights in rise calculation
Cut all stringers before testing first one (costly mistake)
Skip the tread thickness drop cut at bottom (first step too tall)
Allow riser height variations over 3/16 inch (creates tripping hazard)
Install handrail outside 34-38 inch range (code violation)
Space balusters over 4 inches apart (safety hazard, fails code)
Use 2x10 stringers when 2x12 is needed (not enough material remains)