The required height for an outdoor deck handrail in the United States, if the deck is attached to a single-family detached home, is 36 inches minimum, as of 2015. The minimum height for commercial buildings or multi-family buildings is 42 inches.
These heights are required by the International Residential Code, or IRC, and International Building Code, or IBC. The handrails are only required for decks that are 30 inches or higher above the grade. This is required for safety purposes, since someone could fall off the deck and sustain an injury. Even if the deck has a handrail and it is below 30 inches above the grade, the height must still follow the local code requirements. Builders or homeowners should check with local building codes to verify the height.