Do I need a permit for deck construction or replacement in Unincorporated Richland County?

Most likely yes. Deck construction or replacement usually requires a permit in Wisconsin. Confirm the specifics with Unincorporated Richland County.

Decks attached to a home built on or after June 1, 1980, and detached decks that serve an exit, are within the Uniform Dwelling Code under SPS 320.02(1)(g) and (h) and must meet the excavation, footing, frost, load, stair, guard and decay rules listed in SPS 321.225. A deck built to the prescriptive standards in SPS 325 Appendix B is treated as complying with SPS 321.225, per SPS 321.225(2). A detached deck that does not serve an exit is outside the UDC under SPS 320.05(5), so local zoning and building ordinances decide whether it needs a permit. Wisconsin sets no statewide permit requirement for additions or alterations to existing homes; under SPS 320.09(2)(b) those permits are required where the local ordinance requires them, and in a municipality where DSPS has UDC jurisdiction building permits for additions and alterations are not required, though zoning and electrical permits may still apply. This deck is attached to the house or will have a roof. Where a small deck exemption exists at all, it covers only small, low, freestanding decks that do not serve the home's required exit door, so an attached deck falls outside it. A ledger bolted to the house is the most common point of deck failure, which is why departments inspect the footings, framing and ledger connection before the decking goes on. Adding a roof makes the deck a covered structure that is reviewed like a patio cover or addition, including roof framing and, in high wind areas, uplift connections.