What is the minimum rise of a stair if its total rise exceeds 3,800 mm?

To determine the minimum rise of a stair when the total rise exceeds 3,800 mm, it’s essential to refer to the building codes and regulations concerning stair design. Most building codes stipulate that when the total rise of a stair exceeds 3,800 mm, the minimum rise per step needs to typically be set higher to ensure safety and usability.

The common minimum rise per step in these cases is often specified around 125 mm. This is considered a comfortable height for most people to navigate, allowing for a safe ascent or descent without excessive strain. Rises that are lower might lead to a higher number of steps, which can become impractical or create safety concerns if someone missteps or becomes fatigued.

By confirming that 125 mm is indeed the specified minimum rise under such conditions, it’s clear why this option is the correct answer. Other rise options would either not comply with regulations or lead to a stair design that is not functional for higher total rises.