ADU rules in Bluffton

Bluffton's Unified Development Ordinance lists the Accessory Dwelling Unit as a Conditional (C) use in every base district except Preserve (PR): Agricultural, Rural Mixed-Use, Residential General, Neighborhood Core, General Mixed-Use, Light Industrial, all five Old Town historic districts and the Bluffton Village PUD. In this UDO 'Conditional' means permitted subject to the objective use standards of Sec. 4.4, checked by staff, not a hearing. A detached ADU must be an accessory structure in the side or rear yard, no closer to the primary frontage road than the house, one per lot. In the Old Town Bluffton Historic District the ADU takes the Carriage House building form, placed behind the primary structure.

The UDO defines an ADU as a separate, complete dwelling unit with an exterior entrance, kitchen, sleeping area and bathroom 'which is an attached or detached extension to an existing Dwelling Unit', and the Sec. 9.2 definition of Accessory Structure covers attached structures (square footage is delineated where the exterior visual separation occurs). So an attached addition qualifies on the same conditional-use standards as a detached unit. The ordinance does not address converting space inside the existing house (a basement or interior suite) into an ADU, since Sec. 4.4.1.A.4 requires the ADU to be an accessory structure; confirm that route with the UDO Administrator. In Old Town the Carriage House may be attached but must be clearly incidental to, smaller than and distinguished from the principal building.

Sec. 4.4.1.A caps an ADU at 1,200 heated square feet with a maximum footprint of 800 square feet not counting porches, and limits height to two stories or the height of the primary structure, whichever is less. In the Old Town Bluffton Historic District the Carriage House building type carries the same 1,200 square foot ceiling (a 121 to 1,200 square foot range per unit), the same 800 square foot footprint and a height of one to two stories, with garages limited to two cars. District lot coverage and setback rules for the principal lot also apply.

Neither the ADU use standards in Sec. 4.4.1 nor the ADU definition in Sec. 9.4.1 requires the owner to live on the property, at application or afterward. A full-text search of the UDO for 'owner occupied', 'owner-occupied' and 'owner occupancy' finds only the rule for replacing manufactured homes in the historic districts and the workforce housing standards, neither of which applies to ADUs. Proprietor residence is required only for lodging uses such as homestays and bed and breakfasts.

Table 5.11.3.C sets the minimum at 2 spaces per dwelling unit and 1 space per accessory dwelling unit townwide. The Old Town Bluffton Historic District has its own Table 5.15.7.C.1.a with the same 1 space per ADU, but credits on-street spaces directly in front of or adjacent to the property, and the UDO Administrator may review and adjust Old Town parking counts. An ADU used as a short-term rental must also meet the town's one space per bedroom guideline stated on its Short-Term Rentals page.

Sec. 4.3.B defines a Conditional (C) use as 'Permitted subject to specific conditions and specific use standards listed in Section 4.4', distinct from a Special Exception (SE), which goes through a discretionary review process. An ADU is therefore approved administratively through a Zoning Permit reviewed by the UDO Administrator for compliance with the ordinance (Sec. 3.20), plus a building permit. In the Old Town Bluffton Historic District any new structure also needs a Certificate of Appropriateness-HD from the Historic Preservation Commission, a design review rather than a use approval. In PUDs the use is whatever the approved PUD concept or master plan lists.

The UDO places no tenancy, lease-term or separate-sale rule on ADUs. A short-term rental unit is defined as 'a dwelling unit, principal or accessory' rented in its entirety for less than 30 consecutive days, so an ADU can be one. Short-term rental is a conditional use in AG, RMU, RG, NC, GM, the five historic districts and the Bluffton Village PUD (not PR or LI). Since January 1, 2021 new STR units are limited to one per lot in AG, RMU, RG, NC, GM, RV-HD, NCV-HD, NG-HD and NCE-HD, so a house and its ADU cannot both become new STRs there; NC-HD is exempt. Each unit needs an annual STR permit under Code Ch. 6, Art. V (agent on call 24/7, adjacent-owner notice, permit number in every listing), a business license and accommodations taxes; inside a PUD, STRs are subject to development agreements and HOA rules and the town asks for an HOA or POA approval letter.