ADU rules in Evanston

Detached ADUs became legal in Evanston on 3-3-2026, when Ordinance 26-01 added use row 8.1, 'Accessory Dwelling Units,' to the residential use schedule in § 24-15A and enacted a new standards section, § 24-26.1. The answer is zone-dependent: an ADU is a use by right (P8) only in the three Rural Residential districts (RR-E, RR-1, RR-5), it requires conditional use review (C8) in every Low Density Residential district (LR-D, LR-E, LR-E.5, LR-M, LR-M.5), and it is flatly prohibited (an asterisk in the table) in the Medium and High Density Residential districts (MR-E, MR-D, MR-R, HR-E, HR-D, HR-R). Both P8 and C8 point to § 24-26.1, whose 17 standards apply either way. Only one ADU is allowed per lot, only on a lot that already has a detached single-family dwelling, and the lot must either meet the district's minimum lot area or preserve the district's minimum usable open space per dwelling unit.

The same use row 8.1 and the same § 24-26.1 standards govern attached, internal and basement units: Ordinance 26-01 defines an accessory dwelling unit as one that 'may be located within, attached to, or detached from the principal dwelling.' So an attached or basement ADU is by right in the RR districts, conditional use review in the LR districts, and prohibited in the MR and HR districts and in every nonresidential district. Attached ADUs must meet the principal-building setbacks for their district rather than the looser accessory setbacks used for detached units (§ 24-26.1A(7)). A basement ADU is the one form exempted from the square-footage cap and may occupy the entire floor area of the basement (§ 24-26.1A(4)(C)). Conversion of an existing lot with a single-family attached or multifamily dwelling is not an option: § 24-26.1A(1) prohibits ADUs on those lots.

§ 24-26.1A(4)(A) caps a detached ADU at 50 percent of the footprint area of the principal dwelling or 1,200 square feet, whichever is less, with attached garages, porches and decks excluded from the footprint math, and sets a 190 square foot floor. A detached unit of 400 square feet or less (and at least 190) must also comply with IRC Appendix BB, Tiny Houses. Subsection (4)(B) layers on a cumulative cap: all accessory buildings on the lot, the detached ADU included, cannot exceed 75 percent of the principal building's footprint. A basement ADU is exempt from the unit size limit and may fill the whole basement, subsection (4)(C). Two further ceilings bite in practice: every ADU is limited to two bedrooms or sleeping areas (§ 24-26.1A(5)), and a detached unit is held to the 25-foot accessory-use height limit in the § 24-16 bulk tables (principal buildings get 35 feet).

§ 24-26.1A(15) requires the owner to physically live in either the primary dwelling or the ADU as their primary residence for more than 50 percent of a calendar year, and provides that the ADU 'shall not be occupied unless this is the case,' so the duty is ongoing rather than only at application. The council added the 50-percent-of-a-calendar-year language during the readings, explicitly to deter absentee landlords. § 24-26.1A(14) adds a front-end test: the owner must have lived continuously in the principal dwelling as their primary residence for one year before submitting the conditional use permit application (where one is required) and the building permit application, with one exception, an ADU folded into the initial building permit for a new single-family house on an undeveloped or vacant lot. After approval the owner must record a 'Notice of Accessory Dwelling Unit Regulations' containing the legal description with the Uinta County Clerk (§ 24-26.1A(16)). Wyoming has no statute that preempts, caps or otherwise limits local owner-occupancy rules, so the local text stands on its own.

§ 24-26.1A(8) requires one additional off-street parking space for the ADU beyond the minimum the zoning district already requires, and § 24-16 sets that district minimum at 2 off-street spaces per dwelling unit in every residential district, so a house plus an ADU normally means 3 spaces. The space must be paved with asphalt, concrete or a similar dust-free permanent surface and must meet the stall dimensions in § 24-58 (10-foot stall width; 19-foot stall length at 90 degrees). One genuine concession for small lots: an uncovered ADU parking space may sit in a required yard setback abutting a street. Evanston has no transit-proximity or small-unit exemption from the requirement.

The review path is set by zone. In the Rural Residential districts (RR-E, RR-1, RR-5) an ADU is a use by right (P8), so approval is administrative: a building permit under § 24-110 plus compliance with the § 24-26.1 standards. In every Low Density Residential district (LR-D, LR-E, LR-E.5, LR-M, LR-M.5) the table shows C8, conditional use review, which means a complete application to the planning office, staff and referral-agency review, and a public hearing before the Planning and Zoning Commission under §§ 24-10 and 24-39 through 24-42, with a City Council call-up available under § 24-11. In the MR and HR districts no permit path exists at all. Separately, because Evanston zones under W.S. 15-1-601 and applies an adopted International Residential Code, the state Fast Track Permits Act (W.S. 16-13-101 and 16-13-102, effective 7-1-2026) now governs the building-permit clock: a completeness notice within 10 business days, a decision within 30 calendar days of a complete application, written denial reasons within 7 days, and deemed approval if the deadline lapses. That act is a processing law only and does not shorten or replace the conditional use hearing.

Renting is contemplated: Ordinance 26-01's findings recite that ADUs 'may be used to generate rental income.' The binding limits are on occupancy and ownership rather than lease length. § 24-26.1A(13) allows no more than one family in the ADU, and § 24-105 defines family as a person or persons related by blood, marriage or adoption living together in a dwelling unit, which is far narrower than the up-to-eight-unrelated-adults allowance § 24-17 gives ordinary dwelling units; an employed non-family member may occupy the ADU temporarily or intermittently to provide caretaking services for a member of the occupant's family. § 24-26.1A(15) requires continuing owner occupancy of one of the two units, and § 24-26.1A(3) bars subdividing the ADU, segregating it in ownership from the principal dwelling, or reclassifying it as a principal use. Evanston has no short-term-rental ordinance or license: Chapter 11 licenses transient merchants, peddlers and mass events but not residential rentals, and boarding houses, rooming houses and bed-and-breakfasts are prohibited uses in exactly the LR and RR districts where ADUs are allowed (§ 24-15A row 4), while § 24-15 provides that any use category not expressly permitted is deemed excluded. Confirm any nightly-rental plan with the Engineering and Planning Department before relying on it.