The General Shape of a Code-Compliant Residential Stair

• A residential stair must be at least 36" wide. Each tread (the horizontal part of the stair you step on) must be at least 11" wide (no longer 10 1/2"), and the total rise (the vertical distance from tread to tread) may be no more than 7" (no longer 8" or 7 1/4"). This is the 7-11 rule. Tread and riser dimensions may deviate from designed specifications by no more than 3/16" (no longer 5/16" or 1/4"). Stairs must have a minimum of 6 feet, 8 inches of headroom--the minimum distance between any part of the tread and the structure above. A recent survey of 20 or 30 Internet articles on stairs suggests that about half of them provide tread, rise and headroom dimensions that are no longer legal. When in doubt, consult your city's current building code.
  
  

How Many Stairs in a Flight?

• There is no direct code article specifying how many stairs you can have in a single flight, but the total distance from floor to floor (or from floor to landing) cannot exceed 12 feet. The landing itself is also tightly specified in current codes. It may be no less than 36" by 36"; if the stair itself is wider than 36", the landing must then be proportionately longer. A 40-inch wide stair, therefore, would have a landing extending 40" in length and width.
  
  

Regulations related to Noses

• The nose of a stair is that part of the tread that extends beyond the riser. There are no specific regulations for residential stairs governing the minimum or maximum distance from the riser to the farthest extension of the nose; most builders will extend the nose about about 1" or 1 1/2". But what is significant, and often misunderstood, is the relation between the nose and the legal minimum tread width. However far the nose extends beyond the face of the riser is deducted from the calculated legal length. If you have a stair with a 12" tread (as measured across the physical tread) with a 1 1/2" nose, the legal length of the tread is only 10 1/2"--a half-inch less than the required minimum. Nose overhangs may deviate no more than 3/8".
  
  

Hand-Rails and Guard Rails

• Until the last code revision, the required height of a guard rail was 36"; since handrails were specified as being a minimum of 34" and a maximum of 38", you could conveniently build a handrail that was 36", thereby fulfilling both requirements. Now, however, the guardrail must be 42" in height, meaning, in practice that many stairs now must have a 42" guardrail and then, within the guardrail a handrail, usually 36" in height. This is an awkward design problem, but a sensible code modification; Americans are growing taller.
  
  

Balusters and Related Openings

• Balusters are the vertical supports, until recently usually one per tread, that hold up the handrail. Current code regulations, however, specify that a 4" ball may not pass between balusters or in any direction from the tread other than the nose. This means two things: treads cannot have open backs--the physical riser must be either a solid substance or in some other way prevent the 4" ball from rolling off the back of the tread. It also means that it is difficult to build a legal stair with vertical balusters; you can do it, but you will need at least two balusters per tread, otherwise a 4" ball will roll out between them. Contemporary stair design has therefore trended toward functional vertical supports every 3 or four feet supporting a series of piping or cabling parallel to the handrail and spaced on 4" centers.
  
  

Handrail Profiles

• The many current regulations covering the many possible handrail profiles are detailed beyond the scope of this article. The general requirements for a circular handrail are that it be no more than 2" in diameter and no less than 1-1/4" and if the handrail is not circular that the total distance around it be no more than 6" and no less than 4". But special shapes have special requirements. If you want to design an unusual handrail profile, consult your city's building code.