The maximum interior height of an entry door threshold is 1/2 inch, and up to 3/4 inch on exterior siding doors where it is essential to keep water out, as stated by the United States Access Board. These height limits improve wheelchair access to buildings.
Made from wood, plastic, stone or metal, the entry threshold of a door is decorative and it protects doorways from the constant stomping of people going back and forth. A threshold that is too high is a hindrance to anyone with a wheelchair or difficulty walking, as getting over the threshold becomes difficult.
To ensure equal access to buildings, especially at the entryways, the Americans with Disabilities Act Accessibility Guidelines limit the threshold height. In addition, the guidelines require any threshold over 1/4 inch to feature a beveled slope ratio of 1:2.