Lay out a preliminary stair

How the calculator chooses a whole number of risers

A stair cannot have a fraction of a riser. The calculator tests whole counts from two to one hundred. For each count it divides the finished floor-to-floor rise by the number of risers, checks the entered minimum and maximum, assumes the upper floor or landing forms the final arrival surface, and therefore uses one fewer going than risers.

The required straight run equals the number of goings multiplied by the proposed going. A candidate is retained only if that run fits inside the available straight dimension. Among retained candidates, the calculator prefers the riser closest to 175 mm. This preference is merely a repeatable selection method; it is not an NCC target or a claim of comfort.

If there is no candidate, the result explains that the entered rise, going, run and riser range do not combine. Increasing the run, changing the going or designing turns and landings may solve the geometry, but those changes need a complete design. Never squeeze a stair into a space by making a non-compliant or inconsistent step.

The tread surface quantity is proposed going multiplied by stair width multiplied by the number of goings. It is not an ordering quantity for boards, finishes or nosings. Actual tread depth, overhang, support, cuts, landings and wastage must be detailed separately.

NCC 2022 Housing Provisions stair geometry reference

For a stairway other than a spiral stairway, NCC 2022 Housing Provisions 11.2.2 Table 11.2.2a lists a maximum riser of 190 mm, minimum riser of 115 mm, maximum going of 355 mm and minimum going of 240 mm. It also lists a maximum 2R + G quantity of 700 mm and minimum of 550 mm.

The same provision states that a flight must have not more than 18 and not less than 2 risers. Adjacent riser heights and adjacent going dimensions must not vary by more than 5 mm, and the largest and smallest across a flight must not vary by more than 10 mm. There are specified circumstances for variations at landings and winders; those details require the actual provision and design.

The calculator initially loads 190 mm, 115 mm and 18 risers, while the proposed going is entered by the user. It reports whether the calculated R, entered G, 2R + G and flight count fall within those headline ranges. The reference values can be edited because the applicable edition, building class, stair type, state or territory variations and approval pathway must be confirmed for the project.

Do not interpret a green or positive screen as compliance. NCC requirements also address construction, slip resistance, landings, thresholds, doorways, winders, spiral stairs, barriers and handrails. A stair may satisfy numerical rise and going limits while failing in headroom, support, fire safety, access, guarding or other respects.

Measure rise and run from finished surfaces

Total rise is the vertical distance from the lower finished floor to the upper finished floor. Structural drawings alone may omit tiles, timber, carpet, screed or underlay. Even a modest change in final floor build-up alters every riser when the total is divided evenly.

Available run must be measured horizontally and must allow the stair to arrive at safe landings and circulation space. It is not simply the length of an empty room. Doors, corridors, walls, handrails, headroom, floor openings and required landing dimensions can reduce what is usable.

For an upper floor that forms the final landing, there are normally fewer goings than risers in the straight-flight arithmetic used here. If a particular prefabricated assembly or drawing counts treads differently, align definitions before comparing numbers. Confusing tread depth with going is a common source of error: going is measured between nosing points, while the physical tread can extend under an overhang.

Measure at several locations and investigate floors that are out of level. A stair should be set out from an approved datum and adjusted consistently, not forced to absorb a construction discrepancy in the top or bottom riser. The first and final steps are frequent trip points when floor finishes change.

Complete stair design checks beyond the calculator

Housing Provisions do not state a single general minimum width for every Class 1 and 10 stair, but other constraints determine a workable width. Do not use that absence to create an unsafe or unusable route. Furniture movement, handrail projection, wall finishes and emergency movement all need consideration.

Split long stairs into flights and landings carefully

If the selected riser count exceeds the entered maximum per flight, the calculator divides the total by that maximum to suggest the minimum number of flights. It then shows an even-as-practicable riser distribution. This is only a planning prompt. A landing occupies floor area, changes the path and requires its own dimensions, support, headroom and barrier details.

For example, 25 risers cannot be one flight under an 18-riser reference. A two-flight concept might distribute them as 13 and 12. The actual arrangement could be straight with an intermediate landing, quarter-turn, half-turn or another approved configuration. Each option changes the building opening and structural support.

Do not create a one-riser flight to make the arithmetic work; the referenced general flight range starts at two risers. Landings should be readily perceived and should not introduce an unexpected step near a doorway. Confirm the exact NCC clauses for landings and thresholds.

Changes of direction affect handrails and barriers. A continuous handrail, extensions or returns may be required depending on building and stair context. Detail junctions so users do not lose support at the point of turning.

Move from preliminary arithmetic to a buildable set-out

First confirm the site measurement and applicable regulatory pathway. Next prepare a dimensioned plan and section showing every finished level, riser, going, nosing, landing, opening, headroom constraint, handrail and barrier. Coordinate the stair with structural, architectural and services drawings.

Second, select the construction system. Cut timber stringers, housed strings, steel frames, concrete stairs and prefabricated units use different support and connection details. The calculated slope line is not a stringer cut length because bearing, joints, landings and trimming add geometry.

Third, build or verify a full set-out before repetitive cutting. Account for tread and floor-finish thickness. Keep risers and goings consistent within permitted tolerances. Check diagonals, level, plumb and support as work proceeds instead of discovering cumulative error at the upper floor.

Finally, arrange required inspections and retain approvals. Before occupancy, check that temporary edges have been replaced with completed barriers and handrails, fasteners are secure, surfaces are clean and lighting works. Any last-minute finish change should trigger a check of top and bottom riser heights.

Read the result as a coordinated set, not isolated numbers

Suppose total rise is 2,800 mm, the proposed going is 270 mm and the available run is 4,000 mm. Sixteen risers would produce 175 mm risers but need 4,050 mm for fifteen goings, so that otherwise neat option does not fit. Fifteen risers produce approximately 186.7 mm risers and need 3,780 mm for fourteen goings. The screen then checks the riser, going, 2R + G and flight limits together.

This example shows why dividing rise by a preferred riser is only the start. Rounding changes the whole count, which changes the number of goings and run. Moving a wall by a small amount may permit a materially better layout, so stair planning should occur before floor openings and circulation are fixed.

If the result is near a limit, do not design to theoretical perfection. Construction tolerances, floor finishes and measurement uncertainty can push the built stair outside the permitted range. A designer can select dimensions with appropriate tolerance and document how they are controlled.