I wonder do you require a permit when you have a frost depth of 24 to +48 inches with the wall under 4 ft.?
2009 IBC
105.2 Work exempt from permit. Exemptions from permit requirements of this code shall not be deemed to grant authorization for any work to be done in any manner in violation of the provisions of this code or any other laws or ordinances of this jurisdiction. Permits shall not be required for the following:
Building:
4. Retaining walls that are not over 4 feet (1219 mm) in height measured from the bottom of the footing to the top of the wall, unless supporting a surcharge or impounding Class I, II or IIIA liquids.
Commentary; "Structures classified as Group U, such as fences, equipment, foundations, retaining walls, etc., are somewhat outside the primary scope of the code (i.e., means of egress, fire resistance). They are not usually considered to be habitable or occupiable. Nevertheless, many code provisions do apply and need to be enforced (e.g., structural design and material performance)."
In reference to guardrails Virginia (an opinion);
"Retaining walls are Group U structures under the IBC. The guardrail provisions in the IBC are in Chapter 10 (Means of Egress). There is no means of egress associated with a retaining wall as it's not occupied, so the IBC guardrail provisions cannot be applied to a retaining wall. Only open-sided walking surfaces that are part of the means of egress have to have guardrails. Almost every part of the inside of a building is part of the inside of a building is part of the means of egress, so any open-sided walking area inside of a building can't have an unprotected drop-off.
The IRC only applies to the construction of the house, not a retaining wall (that' a Group U structure under the IBC), so you can't use the IRC guardrail provisions to apply out on the lot away from the house."
In Alexandria, Va. they went so far as to require a permit for multiple 2 ft. retaining walls that totals for the entire elevation (for example 2 ft. walls separated by 3 ft. of grade).