In the United States, OSHA provides design requirements for access ladders. However, it is important to confirm the building code requirements for state and local jurisdictions.
OSHA Requirements for Fixed Ladders appear in 29 CFR 1910.27 (Fixed Ladders). The information provided below covers general design requirements. Refer to the OSHA link for full documentation.
In addition, refer to ANSI A14.3-2002, American National Standard for Ladders-Fixed-Safety Requirements.
OSHA Ladder Requirements
Minimum Design Live Load: 200 pounds.
Rung Size: Minimum diameter of 3/4" for metal and minimum diameter of 1 1/8" for wood. The minimum clear width of rungs shall be 16".
Climbing Side Clearance: For 90 degree (vertical) ladders, there shall be 30" of clear space on the climbing side.
Back Side Clearance: The distance from the center-line of rungs to a permanent object behind the ladder (i.e. a wall) shall be 7" minimum.
Safety Cages: Required for ladders greater than 20'-0" in height.
Pitch: Fixed ladders shall have a pitch between 75 degrees and 90 degrees.