Staircase Steps Brazil

Standard Stair Step Sizing (Blondel)

François Blondel's old comfort rule ties riser height h to tread depth p through 2h + p = 63–65 cm, which is roughly how far a person steps on a slope. Brazilian houses usually settle on risers between 16 cm ≤ h ≤ 18 cm and treads between 28 cm ≤ p ≤ 30 cm. That keeps the pitch in the comfortable 30° ≤ θ ≤ 35° band.

Count the risers with n = H / h, round that up to a whole number, and recompute h = H / n so the steps come out even. The horizontal run is then L = (n − 1) × p. For minimum width, NBR 9077 asks for w ≥ 0.80 m in a home and w ≥ 1.20 m on emergency exits or anything used by the public. You also need a landing at least every 19 risers.

Applications

Architects lean on it to lay out internal stairs in houses and duplex apartments. Builders nudge the riser height to soak up variation in floor thickness. Fire safety engineers check emergency stairs against NBR 9077, and during a renovation it tells you whether the old stair still works after the floor was raised or a wooden overlay went down.

FAQ

Why 2h + p instead of slope angle? Blondel's rule tracks the effort each step costs you, not just the geometry. Two stairs at the same angle can use different riser and tread pairings, and they feel nothing alike when you actually climb them.

Can risers be unequal? No. Every riser in a flight has to match, because even a 1 cm difference is enough to catch someone's foot and trip them. If something needs to give, change the run length or the slab depth, and leave the riser alone.

What about spiral or curved stairs? Under NBR 9077 a spiral stair can never be your only emergency exit. It is fine as a secondary internal stair, and there the 28 cm tread is measured 50 cm in from the inner edge.