Quick Answer
Stair stringer length = √(total rise² + total run²) + extra at top and bottom for cuts. For a typical stair with 175mm rise × 250mm going × 14 risers, the stringer is 4.31m long with a 35° pitch. Use 240×45 or 300×45 LVL or hardwood for residential stairs per AS 1684.
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NCC Stair Compliance Limits
For Class 1 (residential) stairs:
- Riser: 115-190mm
- Going (tread depth): 240-355mm
- 2R+G formula: must equal 550-700mm
- Headroom: 2000mm minimum from any nosing
- Maximum risers per flight: 18 before a landing required
Stringer Material Selection
| Stringer Length | Recommended Section |
|---|---|
| Up to 3m | 240×45 LVL or F17 hardwood |
| 3-4m | 300×45 LVL or F17 hardwood |
| 4-5m | 300×63 LVL or laminated section |
| Over 5m | Engineered design, typically intermediate landing |
FAQs
How long is a stair stringer for 14 risers?
For 175mm rise × 250mm going × 14 risers: total rise 2,450mm, total run 3,250mm, diagonal 4,070mm. Add 300mm top fixing: order a 4.4m stringer.
What size LVL for a residential stair stringer?
240×45 LVL is standard for stringers up to 3m. Use 300×45 for 3-4m runs or where the stair is wide and needs three stringers.
How deep do I notch a stringer?
Notch the rise (vertical) and going (horizontal) per the design dimensions. Always leave at least 100mm of solid stringer below the deepest notch for structural integrity.
What is the maximum stair pitch in Australia?
The NCC effectively caps Class 1 (residential) stair pitch at around 41° via the 2R+G formula. Anything steeper fails compliance.
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