Staircase Height & Riser Details
📊 Part K Staircase Geometry Breakdown
Designing a new timber or steel staircase for a UK home extension, loft conversion, or self-build requires strict adherence to Building Regulations Approved Document K (Protection from falling, collision and impact).
Approved Document K sets statutory limits for maximum riser heights (max 220mm), minimum going tread depths (min 220mm), maximum pitch angles (max 42.0°), and the mandatory 2G + R relationship formula.
⚙️ Statutory UK Part K Staircase Rules & Formulas for 2026/27
1. Statutory Domestic Staircase Dimensional Limits (Private Stairs)
Under Approved Document K, private domestic staircases in single dwellings must satisfy:
- Maximum Riser Height (R): 220 mm (ideal domestic riser is 175mm to 190mm).
- Minimum Going Tread Depth (G): 220 mm (ideal domestic going is 240mm to 260mm).
- Maximum Pitch Angle: 42.0 degrees (°).
- Minimum Headroom Clearance: 2.0 metres of clear vertical height above the pitch line.
2. The 2G + R Relationship Formula
To ensure comfortable walking rhythm up and down the stairs, every staircase must satisfy the statutory relationship rule:
- Statutory Formula:
550 mm ≤ (2 × Going) + Riser ≤ 700 mm. - Example: A staircase with a 185.7mm Riser and 250.0mm Going:
(2 × 250.0) + 185.7 = 500 + 185.7 = 685.7 mm.- Result: PASSED (falls comfortably within the 550mm to 700mm limit).
3. Step Calculations from Total Rise Height
- Number of Risers:
Risers = Round[ Total Floor-to-Floor Height (mm) ÷ 185mm ]. - Individual Riser Height:
Riser = Total Floor-to-Floor Height ÷ Risers. - Pitch Angle (°):
Pitch = arctan(Riser ÷ Going) × (180 ÷ π).
📊 Practical Staircase Geometry Worked Examples
Below are two worked calculation examples illustrating Part K staircase math:
- Total Rise Height: **2,600 mm**
- Calculated Risers: **14 Risers** (2,600 ÷ 14 = 185.7mm per riser)
- Target Going Depth: **250.0 mm**
Calculation: Pitch = arctan(185.7 ÷ 250) = 36.6° (<= 42°). 2G + R = (2 × 250) + 185.7 = 685.7 mm.
- Total Rise Height: **2,400 mm**
- Calculated Risers: **12 Risers** (2,400 ÷ 12 = 200.0mm per riser)
- Target Going Depth: **220.0 mm**
Calculation: Pitch = arctan(200 ÷ 220) = 42.3° (> 42° Limit). 2G + R = 640mm. Pitch exceeds 42.0°.
📑 Common Pitfalls & Staircase Warnings
- Forgetting Headroom Clearances Under Sloping Loft Ceilings: A minimum vertical headroom of 2.0 metres must be maintained over the entire flight pitch line. For loft conversions, building control allows headroom to reduce to 1.9m at the center of the flight if headroom rises to 2.0m at the side.
- Balustrade 100mm Sphere Rule: Openings between baluster spindles, open risers, and handrail gaps MUST NOT allow a 100mm sphere to pass through to protect young children from trapping heads.
- Flight Riser Limits: A single flight of domestic stairs must not contain more than 36 risers without an intermediate landing (though domestic homes rarely exceed 16 risers per flight).
❓ Frequently Asked Questions (FAQ)
The **Riser** is the vertical height from the top of one step tread to the top of the next step tread. The **Going** is the horizontal depth from the front nosing of one step to the front nosing of the step above.
Under Approved Document K, handrails must be installed at a height between **900mm and 1,000mm** measured vertically above the pitch line of the stairs.
Space saver / paddle stairs are permitted for UK loft conversions ONLY as a last resort where space prohibits a standard staircase, and only to serve a single room and/or bathroom.
Step treads with open risers must overlap adjacent treads by at least **16mm** under Part K rules to ensure structural safety and prevent foot slippage.