Ramps in general are designed to allow an easier transition from the grade to inside the structure. Not all ramps are needed to be designed to meet the accessibility code. When building a ramp, a permit is required to be obtained, and plans are required, along with the location of the ramp (site plan), and the type of structure it is being attached to, residential or commercial.
For more information:
International Residential Code – 2015
International Building Code – 2015