The Primary Purpose of a Stair or Staircase
Stated simply the primary purpose of a stair or staircase is to get people from one floor level to the next, but it is far more complex that than unfortunately for us designers!
Is the stair to be used as the main stair to the bedrooms or a bathroom, does it take you to a basement? Is the stairs primary purpose moving people, storage access, amenities access or central to the whole buildings function?
Is it all of these?
Identifying these parameters will be the determining factors of your design, along with some other questions that you can find here.
Below is a diagram showing the basic design requirements for treads, risers and angles per type of stair.
Stair Sizing Diagram for Different Types of Stair Uses
These are the most important dimensions for making a staircase comfortable and easily accessible for the user. Most local building authorities will have specific requirements for your area. They will be similar to these as they are the most ergonomically successful, but before you commit to your design, ensure that you have checked with your local building authority for the dimensions required in your area, as changing a stair design at a later date can be difficult as well as expensive.
There are obviously more things to consider when designing your staircase, some of these can be found at Staircase Design Process Questions.
More Information about Stairs