Planning commission debates accessory dwelling unit rules, tables draft for revision

The Warren County Planning Commission discussed a series of proposed zoning text amendments with particular focus on a new accessory dwelling unit (ADU) definition and supplementary regulations. Commissioners asked staff to revise the draft and the commission voted to table authorization to advertise the ADU text amendment until the June meeting.

Why it matters: ADU rules affect how homeowners, families and developers may add secondary housing units on existing parcels. Changes can influence housing supply, subdivision choices and long‑term land‑use patterns in Warren County.

Planning staff proposed replacing the existing “guest house” use with a new ADU use. Under the draft, detached ADUs would be subject to a minimum lot acreage; attached ADUs or ADUs within an existing dwelling would be permitted by right subject to supplementary regulations. Staff initially proposed size limits for ADUs in a window (750–1,500 square feet) that would apply to ADUs generally. Commissioners and staff discussed several points and asked for revisions before advertising the amendment for public comment:

- Minimum acreage: Commissioners debated the appropriate minimum lot size for a detached ADU. Several members suggested 3.5 acres as the smallest reasonable minimum in agricultural zoning to allow septic and well separation and avoid drought/stress on wells; others said 5 acres is a conservative choice. The commission reached consensus to direct staff to prepare a revised draft using 3.5 acres as the minimum for detached ADUs and no acreage minimum for attached ADUs, subject to other setback and utility requirements.

- Size thresholds and location of ADU: Commissioners asked staff to clarify that the 750–1,500‑square‑foot size window should apply to detached ADUs and attached ADUs that expand the building footprint, but not to ADUs that are entirely within an existing dwelling (for example, converting a basement). Commissioners were concerned that applying the square‑foot cap to accessory units within very large primary houses could produce unintended results; staff agreed to refine the wording to distinguish “ADUs located within an existing dwelling” from detached or footprint‑expanding ADUs.

- Septic and well issues: Commissioners emphasized that septic field space and well separation rules can limit where an ADU is feasible. Staff and commissioners discussed requiring independent septic systems for detached ADUs or, alternatively, easements and other arrangements where drain fields serve multiple lots; the draft will clarify health‑department expectations and setback rules.

- Family subdivision interaction: Commissioners discussed the interaction between ADU rules and family subdivisions (a process that allows a lot division within a family). Staff noted a family‑subdivision pathway exists but that requirements for retaining ownership for a period (for example, five years) should be maintained; the draft will include clarifying language to avoid enabling easy short‑term subdivision for rental purposes.

After extended discussion staff agreed to revise language addressing these points. Commissioners voted to table authorization to advertise the ADU text amendment (Z2025‑0501) until the June meeting; several companion text amendments (agritourism, agricultural pursuits in other districts, and subdivision ordinance changes) were authorized for advertisement at this meeting after staff review and tweaks.