What does the unit rise of a stair refer to?

The unit rise of a stair specifically refers to the height of each riser, which is the vertical portion of the stair that forms the step height. This measurement is essential in stair design and construction because it helps determine how steep or comfortable a staircase will be. Building codes often specify a maximum height for risers to ensure safety and accessibility. When planning a staircase, knowing the unit rise helps in calculating the total height of the stairs and the overall design of the staircase.

Understanding this concept is vital for ensuring that the stairs are not only functional but also meet safety standards, which include considerations for balance and ease of use. In contrast, the other choices do not accurately define the unit rise: the height of the tread refers to the part you step on rather than the riser, the total height encompasses more than just individual risers, and the angle of incline is a different measurement related to the overall geometry of the staircase.