How Many Steps & Stringer Length for a 7.5 ft (90") Rise?
Deterministic framing schedule and stringer cut list for a 7.5 ft (90") vertical elevation (Standard Residential Basement with 10" Joist Header). Calculated with 12 uniform risers (7.5" unit rise), meeting strict International Residential Code (IRC Section R311.7) tolerances.
Exact unit rise: 7.5" (≤ 7.75" max)
11 treads @ 10" depth
Diagonal span: 11.84 ft
Blondel comfort score: 25" (ideal)
Stair Stringer Layout & Framing Cut List
Field layout dimensions for laying out 2x12 stringers with framing square and stair gauges.
| Stair Framing Dimension | IRC R311.7 Standard & Rule | Calculated Metric | Shop / Field Cut Value |
|---|---|---|---|
| Unit Riser Height | IRC R311.7.5.1: Maximum 7-3/4" (197 mm); uniform within 3/8" | 7.5" | 12 Risers @ 7.5" |
| Unit Tread Run Depth | IRC R311.7.5.2: Minimum 10" (254 mm); 11" standard for exterior decks | 10" | 11 Treads @ 10" |
| Total Horizontal Run | Horizontal footprint from bottom riser plumb line to top header | 110" | 9.2 ft (110") |
| Diagonal Stringer Span | Calculated hypontenuse span: √(Rise² + Run²) | 11.84 ft | Buy 14-ft 2x12 Lumber |
| Bottom Stringer Drop Cut | Cut bottom of stringer by tread thickness so bottom step height matches | Mandatory Cut | Trim 1.0" off bottom |
| Minimum Stringer Throat Depth | Uncut diagonal meat of 2x12: ≥ 3.5" IRC minimum (5" recommended) | 5.25" Throat | Full Structural Integrity |
| Number of Stringers Required | 36" clear width @ 16" on-center spacing (4 stringers for composite deck) | 4 Stringers | 4× 2x12 × 14' |
IRC R311.7 Mandatory Code Checks for 7.5 ft (90") Elevation
This schedule specifies 7.5" per riser, safely below the 7.75-inch legal limit to prevent tripping hazards during ascent.
Maintain at least 80 inches of vertical clearance from the stair nosing line to any ceiling header or floor opening above (IRC R311.7.2).
Includes master stringer layout, pattern cutting with circular saw/handsaw, blocking, and tread installation.
Includes 4× 2x12 stringer boards (14ft), tread stock, risers, and structural fasteners.
Conforms to the 2 × Rise + Run = 24" to 25" biometric stride length standard.
Need Custom Tread Thickness, Nosing, or 48" Width?
Launch our live Stair Design & Stringer Calculation Engine to adjust custom stair widths, nosing overhangs, stringer spacing (12" vs 16" O.C.), and print an official itemized material proposal.
Frequently Asked Questions: 7.5-Foot Basement Stair Stringer (90" Rise)
How many steps (risers and treads) are needed for a 7.5 ft (90") total rise?
A 7.5 ft (90") total rise requires exactly 12 risers and 11 treads. Every riser will be identical at 7.50 inches high, conforming strictly to the IRC maximum riser limit of 7.75 inches.
What size lumber should I buy to cut stringers for this staircase?
You should purchase standard 2x12 pressure-treated lumber (for exterior decks) or framing-grade SPF (for interior stairs) in 14-foot lengths. Always buy boards at least 1 to 2 feet longer than the diagonal span to accommodate plumb and seat cut scrap.
How deep must the uncut stringer throat be after cutting the notches?
Per IRC Section R311.7 and building safety standards, the uncut portion of the 2x12 stringer (the 'throat') must be at least 3.5 inches deep (5 inches recommended for outdoor decks) to prevent catastrophic structural split failure under heavy dynamic loads.
How many stringers are required for this flight?
For standard 36-inch residential interior stairs, install a minimum of 3 stringers (spaced 16" on-center) to eliminate stair squeaks and provide solid center support under hardwood or pine treads.