Planning
Stair headroom: what to check before building
How stair headroom depends on the floor opening, slab thickness and finishes, and the layout mistakes that cause clearance problems near the top of a flight.
Stair headroom is a 3D problem
Stair headroom depends on where each step sits, the ceiling or slab above it, and the stairwell opening. A side view is usually the quickest way to spot a clash.
Trouble usually shows up near the edge of the upper floor, where you are already high on the stair but not yet under the opening.
Model the opening early
Add the opening length, opening offset and floor thickness as soon as you can, before you settle the stair in plan.
A stair with good rise and run can still fail if the opening starts too late.
Leave room for finishes
Finished floors, ceiling linings and stair nosings all eat into usable clearance. Work with finished dimensions where you can.
If you are unsure, model on the cautious side and check local requirements before construction.
Put this into practice
Open the editor and test these numbers on your own staircase, with live drawings and a comfort score. No account needed.
Related guides
Planning
Common stair design mistakes to avoid
Stair design mistakes that surface late: fixing the step count too early, leaving headroom and openings until the end, and ignoring how people move around.
Stair calculations
How to calculate stair rise and run
Work out stair riser height, going, pitch and total run from your floor-to-floor height, with the typical ranges to aim for before you build.
Comfort
Using the Blondel formula for comfortable stairs
What the Blondel formula (2h + g) measures, why the target sits near 600 to 640 mm, and how to use it to balance riser height and tread depth.