Do I need a permit for retaining wall construction in Unincorporated Nicholas County?

It depends. Whether retaining wall construction needs a permit in Unincorporated Nicholas County comes down to the details of your project.

Kentucky does not require a building permit or inspection for a single-family dwelling unless the local government has passed an ordinance creating a residential inspection program (KRS 198B.060 and 815 KAR 7:125, Section 2(2)(a)), so the first question is whether the city or county covering the address has one. Where a local program exists, retaining walls not over 4 feet high, measured from grade at the bottom of the wall to the top of the wall, are exempt from a building permit (KRC Section R105.2); taller walls are not. A retaining wall with more than 30 inches of grade difference that is closer than 3 feet to a walk, path, or driveway on the high side must have a guard (KRC Section R312.2). Kentucky law requires anyone planning excavation to notify the underground utility protection notification center at least 2 full working days before starting (KRS 367.4911). This wall will hold up a driveway, patio, structure or sloped ground, which puts extra load on it (a surcharge). Model code exemptions for short retaining walls specifically exclude walls supporting a surcharge. Surcharged walls commonly need an engineered design, drainage behind the wall, and an inspection, because a failure can undermine whatever sits above it.