ADU rules in Boulder City

Boulder City has no accessory dwelling unit provision anywhere in Title 11, and detached backyard units are affirmatively barred. In the R1 zone the only residential use permitted is 'One-family dwelling of a permanent character in a permanent location', and accessory structures are allowed only on the condition 'that none shall be rented or occupied for gain, and that no accessory buildings shall be inhabited'. The Mobile Home Park zone repeats the same bar. The city's Planning Division FAQ states the rule plainly: on an R1 lot you cannot build a mother-in-law quarters or guest house, 'detached buildings are not permitted for living or sleeping purposes', and a detached building may be a garage, workshop, home office, pool house or music room 'but with no bedrooms or kitchen'.

There is no attached, internal, basement or garage-conversion ADU category in the code. Title 11 defines a dwelling unit as a residence 'for one family only, living independently of other families or persons, and having only one kitchen and its own sanitary facilities included in the unit', so a second kitchen inside an R1 house creates a second dwelling unit that the zone does not permit. The city FAQ says you may add bedrooms but 'nothing that could be locked off and used as a separate dwelling', and that 'Variances are not allowed for additional dwellings in a single-family zone', which tracks §11-32-3A: 'In no case shall a variance be granted to permit a use other than a use permitted in that zoning district.' Second units exist in Boulder City only as duplexes in the R2 and R3 zones, which are separate principal uses with their own doubled lot-area minimums, not accessory units.

Because nothing can be lived in, the only size caps that matter are the accessory building limits in §11-20-2B3, applied to the aggregate gross floor area of all accessory buildings on the lot: R1-7 700 sq ft (1,000 if the new detached building matches the primary dwelling in material and color), R1-8 800 (1,000 if similar), R1-10 1,000 (1,250 if similar), R1-15 1,000 (1,500 if similar), R1-20 and R1-40 2,000, R1-80 3,000, R2 800, and ME and MP 600. Fully below-grade basements of accessory buildings are not counted. Height may not exceed one story or 16 ft (§11-20-2B4), dropping to 8 ft when the structure sits less than 5 ft from a side lot line. The table does not list the R1-5 zone. For comparison, a primary dwelling itself has a minimum size (800 sq ft in R1-5 up to 1,500 sq ft in R1-10 and larger zones), not a maximum, subject to lot coverage of 30 to 45 percent.

There is no ADU to attach an owner-occupancy condition to, so the code states no rule. What R1 does impose is a use restriction on accessory structures rather than on the owner: accessory uses and structures are permitted only if 'none shall be rented or occupied for gain', which forecloses renting a backyard building whether or not the owner lives on site. Renting out the single primary dwelling is not restricted by Title 11, and §11-3-3C separately allows a resident family to keep up to two nontransient boarders or lodgers in a one-family residence.

Boulder City sets no ADU parking standard because the use does not exist. The general residential standard in the §11-23-2D table is unusually high: 'Dwellings, single-family, two-family and mobile home estates' require '3 spaces for each dwelling unit, including garage and/or carport'. So a lawful second unit (a two-family dwelling in R2 or R3) has to add three more off-street spaces, not one. Multiple-family dwellings and residential condominiums require 2 spaces per unit plus an extra 20 percent set aside for RV and boat-trailer storage.

No permit path for an ADU exists: the use is not listed as permitted or conditional in any residential zone, and Chapter 30 conditional uses in R1 cover only public and quasi-public buildings, private schools, educational, religious and cultural uses, tract offices, recreational facilities, childcare and community residences, and private heliports in R1-80. A variance cannot open the door, because §11-32-3A bars any variance 'to permit a use other than a use permitted in that zoning district'. The one theoretical hook is §11-20-2A, which lets the community development director decide whether an unlisted use is permitted or conditional in a zone (appealable to the planning commission after a hearing), but that cannot override the express §11-3-3B prohibition on inhabited accessory buildings, and the city's published FAQ answer is a flat no. Anything that does add a dwelling unit also needs a residential allotment under the voter-adopted Controlled Growth Management Plan.

Two separate rules bite. First, §11-3-3B permits accessory uses and structures only if none is 'rented or occupied for gain', so even a legal detached workshop or pool house cannot be let out. Second, Boulder City bans short-term rentals outright: Ord. 1797 (adopted 3-26-2024, effective 4-18-2024) added the Title 11 definition of a short-term rental as a dwelling unit or portion of one 'rented in exchange for remuneration for occupancy for a period of less than 30 consecutive calendar days', listed 'Short Term Rentals' among prohibited home occupations in §11-29-3N, and amended the abatement and penalty sections. The city's notice page records the 4-1 council vote, states that city code had not allowed STRs as a permitted or conditional use even before the clarification, and warns of fines of up to $500 per day. Long-term rental of the single primary dwelling is unrestricted by Title 11, and up to two nontransient boarders or lodgers are allowed in an occupied one-family residence.