[shalini mittal]

Determining Run of Staircases

In a straight staircase, there will always be one fewer stair tread than riser. This is to account for the additional rise needed to meet up with the top floor. Using this rule of thumb to refer back to the previous example of the 104” floor to floor 13 rise staircase, there will be 12 treads.

[FDArchitects]

1. Rule of a step size 
The correct dimensions of a comfortable and efficient staircase according to its use can be calculated using formula developed by French architect François Blondel. in his book Cours d'architecture (1771)


2 Risers + 1 Tread = 60-64 cm 


This correlation was based on his observations over the step length in horizontal plane and leg raise in vertical plane. The step length is considered to be an average step length of an adult person by regular walking along the horizontal plane, and it has a value from 60 to 64 cm. Convenient leg raise in vertical plane makes about 31 cm. Based of these figures, the rule of a step size is deduced.



2. The rule of convenience : 
 tread - riser = 12 cm
and it is applied for design of stairs with a pitch angle of about 30 degrees. 



3. The rule of safety : 
 tread + riser = 46 cm