Staircase Design & Rise/Going Calculator

Staircase Design Guide

What should I know about Building Regulations Part K?

For private domestic stairs (Part K 2013): riser height: 150mm minimum, 220mm maximum. Going: 220mm minimum. Pitch: maximum 42°. The rule: 2 × rise + going should be between 550-700mm (the 'comfort formula'). For the optimum staircase: rise 170-175mm, going 250-260mm. 2×170+260 = 600mm — centre of the comfort zone. Headroom: minimum 2000mm measured vertically from the pitch line. Handrail: required on at least one side if stair is 1m or wider; both sides if over 1m. Height: 900mm minimum from the pitch line, measured vertically to the top of the handrail.

What should I know about Calculating Step Dimensions?

Finding the right number of steps: divide total rise by approximate desired riser (175mm). Round to nearest whole number. Actual riser = total rise / number of risers. Going = available going / (number of risers − 1). Note: number of goings = number of risers − 1 (there is always one fewer tread than riser). Example: 2600mm rise, 3200mm available going. At 175mm target riser: 2600/175 = 14.86 → try 15 risers. Actual riser: 2600/15 = 173.3mm ✓. Going: 3200/14 = 228.6mm — comfortably above the 220mm minimum, giving a safe and practical step depth for this particular staircase design.

What should I know about Winders and Space-Saving Stairs?

Space-saving options: space-saver (paddle) stairs: alternating deep and shallow treads. Maximum pitch 55°. Only suitable for access to single room (loft). Winders: triangular treads that turn the stair direction. Complex to construct — must maintain minimum going at centreline of the stair. Minimum 50mm going at the narrow end. Spiral stairs: compact, but limited accessibility. Must meet minimum 150mm going at inner edge. All spiral stairs require planning if used as primary access. Building Control approval is needed before installing a spiral or winder staircase as the sole means of escape, given the accessibility and safety trade-offs involved.

What should I know about Stringer and Materials?

Closed stringer: solid timber with housing for treads and risers. Traditional, clean look. Open stringer (cut stringer): timber with notches cut for each step — treads visible from the side. Contemporary look. Stringer length = √(total_rise² + total_going²). This is the hypotenuse of the stair triangle. Materials: domestic stairs — softwood (pine, spruce) is standard for painted finish. Hardwood (oak, ash) for natural finish — expensive but durable. Engineered oak: more dimensionally stable than solid oak and less expensive, while still giving the same natural wood finish and appearance.

What should I know about Open Plan vs Closed Staircase Designs?

An open-riser (or 'open tread') staircase, with gaps between treads and no solid riser board, must meet an additional safety requirement under Part K: the gap must not permit a 100mm sphere to pass through, specifically to prevent small children getting a foot or head trapped. This typically limits the vertical gap between treads to under 100mm minus the tread's own thickness consideration, which in practice constrains how 'open' the design can genuinely look while remaining compliant. Closed-riser stairs have no such gap restriction since there's no gap at all. Open-riser designs are popular for their light, modern appearance and often work well with glass or slim metal balustrades, but cost more to build precisely because each tread must be a free-standing structural unit (often needing a substantial stringer or steel support) rather than relying on risers for part of its strength.

What do I need to know about Staircase Load Calculations?

UK Building Regulations require domestic staircases to support a minimum design load, typically specified as 2.0 kN/m² (uniformly distributed) for ordinary domestic use, significantly less than the 4.0 kN/m² or higher required for stairs in public or commercial buildings expecting heavier footfall and more concentrated point loads. This matters for timber stair stringers and tread thickness: a stair designed only to domestic load standards is genuinely a different (and cheaper) structural specification than one built to commercial standards, and retrofitting a domestic stair for commercial or higher-traffic use (such as converting a house into flats with shared stair access) can require significant structural upgrading, not just cosmetic changes, to meet the higher load requirement safely.

What should I know about Fire Escape Stair Requirements?

Staircases that double as a means of escape in a fire — which includes most domestic staircases serving upper floors — have additional requirements beyond the basic rise, going, and headroom rules in Part K. Building Regulations Part B requires that escape routes, including stairs, are protected from smoke and fire for long enough to allow safe evacuation, which is why stairwells in houses with more than two storeys often need fire-resisting doors (typically FD30, 30-minute rated) to rooms off the stairwell, and why open-plan stairs rising through more than one floor without any separation can trigger additional fire-safety conditions. In blocks of flats and HMOs, protected stairways with fire doors and fire-rated construction are mandatory, and a single stair often cannot serve as the only escape route above a certain height without a secondary means of escape. For a loft conversion specifically, the stair to the new floor must not discharge into a room that is itself a dead end relative to the final exit. Always check Part B alongside Part K when designing a stair that forms part of an escape route, and involve a Building Control surveyor early for anything beyond a simple single-storey replacement.

Handrail and Balustrade Requirements

UK Building Regulations Approved Document K requires a handrail on at least one side of any staircase with more than two risers, and on both sides where the stair is 1 metre or wider. Handrail height must be between 900 mm and 1,000 mm, measured vertically above the pitch line (the imaginary line connecting the nosings of each tread). Guarding (a balustrade or similar barrier) is required wherever there is a fall of more than 600 mm, with a minimum guarding height of 900 mm beside a stair and 1,100 mm beside a landing. Baluster spacing must not allow a 100 mm sphere to pass through, the same child-safety rule used for open-riser gaps, to stop a young child's head or body becoming trapped or a fall occurring between the rails.

Worked Example: Sizing a Staircase for a 2,600 mm Floor-to-Floor Rise

A loft conversion needs a staircase for a total rise of 2,600 mm. Starting from the 'comfort formula' target riser of around 175 mm: number of risers = 2,600 ÷ 175 = 14.86, rounded up to 15 risers. Actual riser height = 2,600 ÷ 15 = 173.3 mm (within the 150-220 mm regulatory range). With 15 risers there are 14 goings (one fewer going than risers). Aiming for the comfort-formula target going of about 250 mm gives a total run of 14 × 250 = 3,500 mm. Checking the comfort formula itself: 2 × riser + going = 2 × 173.3 + 250 = 596.6 mm, comfortably inside the recommended 550-700 mm band. Pitch angle = arctan(riser ÷ going) = arctan(173.3 ÷ 250) = arctan(0.693) ≈ 34.8°, well under the 42° regulatory maximum, so this design is compliant on rise, going, comfort formula, and pitch all at once.

Nosing and Tread Overlap

Part K also governs the nosing — the small overhang where one tread's front edge projects slightly over the tread below it. Where goings are below about 250 mm, a nosing overlap of around 16-25 mm is typically required between successive treads, effectively adding a little extra usable foot-room without increasing the actual going measurement used for the regulatory calculation. Like riser height, nosing projection must stay consistent from step to step: an uneven nosing is just as much of a trip hazard as an uneven riser, because the foot's sense of where the next edge will be relies on every step behaving identically. Nosings are usually rounded or chamfered rather than left as a sharp square edge, both for safety underfoot and because a sharp 90° nosing edge is more prone to chipping and wear over time.

Landing Size Requirements

Part K requires a landing at the top and bottom of every flight, and at any point a flight changes direction, with a minimum landing length at least equal to the width of the stair (measured in the direction of travel). Landings must also be kept clear — a door should not swing across a landing within around 400mm of the bottom of a flight in a way that could knock someone standing there, and nothing should be positioned where it would obstruct the final step down onto the landing. Where a staircase splits into separate flights joined by a landing (rather than running as one continuous flight with winders), each individual flight is checked against the maximum-12-risers-without-a-landing guidance separately, which is part of why long stair runs in larger properties are so often broken into two or three shorter flights joined by landings rather than built as one continuous run.