Carbondale planning panel recommends UDC changes to expand ADU options, set 190‑sq‑ft minimum

The Carbondale Planning and Zoning Commission voted unanimously on Jan. 8 to recommend that the Board of Trustees approve a package of amendments to the town's Unified Development Code governing accessory dwelling units (ADUs). The package includes aligning UDC language with the International Building Code (IBC), explicitly permitting ADUs on single‑family homes and duplexes, adopting the IBC's 190‑square‑foot minimum for livable ADU units, and clarifying parking and certain OTR lot‑coverage issues.

Staff presenter Jared Mork told the commission the work should be "bifurcate[d]" into two parts: the code amendments ready for recommendation and several larger items that may need additional review, such as PUD amendment procedures and OTR lot coverage. "If you feel comfortable with the regulations as drafted ... I think we can move forward with the recommendation of approval to the board of trustees," Mork said during the presentation.

Why it matters: supporters said the changes will streamline permitting and expand lower‑cost housing opportunities without creating new, unregulated development pathways. Commissioners repeatedly framed the work as a step toward efficiency requested by the Board of Trustees and a tool to encourage "creative density" that can help residents, including multi‑generational households and workforce residents, remain in town.

Key provisions and decisions

- Duplexes: Staff proposed—and commissioners supported—adding explicit language that ADUs are permitted on parcels with an existing single‑family detached dwelling or a duplex, so each half of a duplex could apply for an ADU if the lot and other code requirements are met. Staff noted that, under current code interpretation, a duplex half already could apply, but the amendment would make that permission explicit to avoid confusion.

- Minimum size: The commission debated minimum livable size (options discussed included 250 and 300 sq. ft.). The majority opted to follow the IBC standard and proceed with 190 sq. ft. as the minimum for livable ADU space, deferring to the building code's technical judgment.

- Maximum ADU size and bedrooms: Staff confirmed the recommended maximum ADU footprint in the draft is 1,000 sq. ft. The commission agreed to raise the bedroom allowance from one to two; a two‑bedroom ADU would generally require Planning & Zoning Commission review rather than administrative sign‑off.

- Parking: The draft reduces certain parking metrics and proposes default one‑space off‑street parking per ADU (or per bedroom), with a process for applicants to demonstrate on‑street parking sufficiency to request relief. Staff said the 500‑sq‑ft threshold for the driveway/parking exemption was tightened to avoid misuse; commissioners suggested simple evidence (time‑stamped photos) as acceptable proof of neighborhood parking availability.

- Short‑term rentals: Commissioners asked whether existing short‑term rental licenses would be grandfathered if a prohibition is adopted; staff said the expectation is trustees would allow current license holders to continue to reapply until their license lapses but would not permit new licenses thereafter.

- OTR and PUD processes: The commission declined to adopt a standalone lot‑coverage density bonus for the OTR zone and instead recommended that the Board and staff consider district‑wide dimensional adjustments and look further at PUD amendment procedures. Staff added a condition recommending the Board consider impervious lot‑coverage revisions for OTR and the commission proposed a joint work session with the Board of Trustees to address PUD amendment process concerns.

The vote and next steps

A commissioner moved to recommend approval of the UDC amendments, with the conditions and findings listed in the packet; the motion was seconded and carried unanimously. The commission's recommendation will be forwarded to the Board of Trustees for formal consideration and public noticing. Staff said the amendments will be refined to align the UDC and building‑code appendix and that the commission will be shown a revised draft in a future meeting before the Board hearing.

What was not decided or remains to be resolved

Commissioners flagged several items for further work or clarification, including: whether to expand impervious‑lot‑coverage relief beyond the OTR district, more precise language on duplex definitions and property‑owner consent in attached units, and whether some PUD amendment pathways should be expedited or addressed through a separate code amendment. Staff recommended additional P&Z review and a possible joint work session with the Board of Trustees to resolve those larger policy issues.

The commission's packet and revised draft will be posted as staff prepares the materials for the Board of Trustees hearing. The commission's formal forwardable recommendation will appear on the Board's agenda for a noticed meeting.