Necessity
California building codes require a handrail for a stair when there are four or more stair risers. Furthermore, the rail must extend one foot beyond the bottom and top tread, as well as along landings for the stair.
Handrail Requirements
California building codes require the stair handrail to be 34 to 38 inches above the nosing of the stair. The handrail must be grippable and between 1 1/4 and 2 inches in diameter. The handrail must have a gap from the wall 1 1/2 inches or more, but the overall handrail must not project more than 3 1/2 inches into the stairway. Handrails along a stairway open to below must not allow a 4-inch sphere to pass through the handrail.
Handrail Forces
Handrails must be able to withstand a 200 pound point load in any direction. In other words, a handrail should not be damaged when 200 pounds is exerted on it sideways, upwards or downwards.
Stairway Widths
The handrails must allow a clear width of at least 36 inches, however stairway widths for buildings other than single-family residential are dictated by the occupancy of the building and individual floors. Buildings with an occupant load less than 50 can have stairs 36 inches wide, while occupancies greater than 50 must have stairs at least 44 inches wide. Stairways with a width greater than 88 inches must have handrails every 88 inches on center.
Guardrail
Buildings other than single-family residential structures must have guardrails for stairs, floors and landings that are more than 30 inches above the floor or ground surface below. These guardrails must be at least 42 inches in height and have handrails 34 to 38 inches above the finished floor. The guardrails must resist, in any direction, a force of 50 pounds per linear foot or a 200 pound point load. The guardrail also must not allow a 4-inch sphere to pass through the rail assembly.