Stair proportioning rule of thumb: For comfortable stair design, which empirical relationship between rise (R) and tread (T) is commonly used?

Introduction / Context:

Stair ergonomics rely on a balance between rise (vertical step height) and tread (horizontal going). Designers use empirical rules to produce safe and comfortable stairs suitable for typical stride lengths and building uses.

Given Data / Assumptions:

• Rise R and tread T in centimetres (cm).
• Standard comfort for everyday occupancy buildings.

Concept / Approach:

A widely cited rule of thumb is 2R + T ≈ 60–65 cm. This reflects human gait mechanics: higher risers require shorter treads and vice versa. For exam purposes, the baseline value 60 cm is often used for quick checks and proportioning.

Step-by-Step Solution:

Verification / Alternative check:

Code guidance often also checks ancillary rules such as R + T ≈ 45 cm and constraints on minimum tread and maximum rise, which align with the 2R + T relation.

Why Other Options Are Wrong:

• R + 2T = 60 and other variants are not the standard comfort equation.
• Equations with 30 cm totals or numerically incorrect expressions do not reflect human ergonomics.

Common Pitfalls:

• Mixing units (inches vs cm) or applying the relation without meeting code minima for tread and maxima for rise.

Final Answer:

2R + T = 60