Can I build an ADU in St. George?

Yes, St. George allows one ADU on any lot with a single-family home, provided an owner lives on the property and the unit is never rented short term. The rules are in St. George City Code 10-17A-3, which the city council amended in August 2026, and they are more permissive than most buyers expect on size and lot, and stricter on occupancy.

The thing that trips people up in St. George is vocabulary. Locals call any small separate unit a casita. The city code does not. In the code, “casita” means a guesthouse, and a guesthouse is a different and much more limited thing than an accessory dwelling unit. If you are planning to rent the unit, that distinction decides whether the plan is legal.

What the St. George ADU ordinance says

These are the standards in St. George City Code 10-17A-3 as amended by Ordinance 2026-068 on August 20, 2026, checked October 2026. ADUs are a permitted-with-standards use in the city’s single-family residential zones (St. George City Code 10-7B).

Rule	What the code requires
How many	One ADU on any lot with a single-family home. A second is allowed downtown, or on lots of at least 11,000 square feet if one is attached and one detached. Never more than two.
Owner occupancy	An owner must live on the property, in either the house or the ADU
Short-term rental	Not permitted in an ADU
Who can live in it	No more people than the code’s definition of a family
Parking	One additional off-street space per ADU; no tandem parking; garage spaces lost to a conversion must be replaced if the house would fall short
Selling separately	Not allowed unless it meets subdivision rules
Permits	An accessory dwelling permit on top of any building permits
Renting it	A recorded deed restriction that the house stays owner-occupied, plus a rental dwelling business license

The code’s definition of a family allows, among other combinations, an immediate family plus one unrelated person, or up to four unrelated people living as one household (St. George City Code 10-2-1).

Internal versus detached

An internal or attached ADU, a basement apartment, a converted wing or an addition, can use an existing entrance to the house or a new one on the side or rear. Basement stairs may reach up to four feet into a side or rear yard, and exterior stairs to an upper-level unit must not be visible from the street.

A detached ADU has its own setback rules:

	One story	Two stories
Rear and side lot lines (rear yard)	Zero feet	Same setbacks as the house
Front, street side and side yards	Same setbacks as the house	Same setbacks as the house
Separation from other buildings	Six feet minimum	Six feet minimum
Height	25 feet maximum	25 feet maximum
Size	Smaller than the house’s gross floor area	Smaller than the house’s gross floor area

Source: St. George City Code 10-17A-3, checked October 2026.

A detached unit cannot sit over a utility easement without written approval from the joint utility committee and an agreement approved by the city attorney, and it cannot drain stormwater onto a neighbor. A detached unit in the rear yard that is shorter than the house does not have to match it; one in a side yard, in front, on a corner lot, attached, or taller than the house must match the roof form, materials and colors. An existing, legally built accessory structure can be converted to a detached ADU if it meets the same standards.

Why a casita is not an ADU in the code

St. George’s definitions say it directly: “Casita: See Guesthouse” (St. George City Code 10-2-1). And the guesthouse rules in 10-17A-7 are written for family and visitors, not tenants:

	ADU	Guesthouse (“casita”)
Can it be rented?	Yes, long-term, with owner occupancy, a deed restriction and a rental license	No. Only for the household or nonpaying guests, with a deed restriction against rental recorded before the building permit
Kitchen	Allowed	Not allowed. A microwave, a compact refrigerator and a small wet bar sink only
Size	Smaller than the house	150 to 400 square feet
Minimum lot	None in the ADU section	8,000 square feet, except in some planned developments
Height	25 feet	15 feet with a gable roof, 12 feet with a flat roof
Separate utility meter	Not addressed in the ADU section	Not allowed
Convert an existing shed or garage?	Yes, if it was legally built and meets the standards	No. New construction only

Source: St. George City Code 10-17A-3 and 10-17A-7, checked October 2026.

So when a contractor or a listing says “casita,” ask which one. A pool house with a bed and a bath is a guesthouse. A unit with a kitchen meant for a tenant needs to be permitted as an ADU. Building the first and using it as the second is the mistake I most want buyers and owners to avoid, and it is the same question I raise in buying a house that already has a casita.

What Utah law adds

Two state statutes sit underneath the city’s ordinance.

Internal ADUs. Utah Code 10-21-303 (formerly 10-9a-530, renumbered in November 2025) makes an internal ADU a permitted use in any area zoned primarily for residential use. A city may require one extra parking space, require a rental license, require owner occupancy for rental, ban rentals under 30 consecutive days, and prohibit internal ADUs on lots of 6,000 square feet or less. A city can also record a notice against the property and, after notice and a chance to cure, hold a lien of up to $100 a day for violations (le.utah.gov, checked October 2026).

Detached ADUs. Utah Code 10-21-304, enacted in the 2026 General Session and effective October 1, 2026, requires the cities it covers to allow a detached ADU on single-family lots of 11,000 square feet or more, bars them from requiring a conditional use permit in a primarily residential zone, and caps required parking. St. George’s August 2026 amendment already allows detached units on smaller lots than that.

Short-term rental is a separate question, and the answer is no

St. George’s code defines a short-term residential rental as a stay of 29 consecutive days or less (St. George City Code 10-2-1), and both the ADU and guesthouse sections prohibit it outright. That holds even if the main house sits somewhere nightly rental is allowed. Where short-term rentals are allowed in St. George covers the zones and overlays for the house itself.

Long-term rental is legal, but it is a business. St. George makes it unlawful to operate a rental dwelling unit without a business license (St. George City Code 4-7-3), and the ADU permit asks for that license as part of the application.

The HOA is a second gate, mostly for detached units

Utah’s Office of the Homeowners’ Association Ombudsman says state law bars an HOA from prohibiting an internal ADU on an owner’s lot, citing Utah Code 57-8a-209 and 57-8a-218, and that an association generally cannot ban renting an internal unit that meets safety codes. Detached ADUs are different: the Ombudsman says an HOA can prohibit them even where the city allows them (Utah Division of Corporations and Commercial Code, checked October 2026).

That makes the detached casita-style unit, the one most St. George buyers picture, the one most exposed to the CC&Rs. Read the architectural rules and any limits on accessory buildings before you pay for plans. How HOAs work in Washington County covers what associations here typically control.

What the code does not settle

The ordinance tells you what is allowed. It does not tell you what a project costs. Impact and connection fees, the building permit, sewer and power capacity, and the engineering are all separate, and none of them are in 10-17A-3. Ask the city’s community development department for the current fee schedule on your specific plan.

The ground matters too. A detached unit is a new foundation, and much of St. George sits on soil that needs engineering; whether St. George soil is bad for foundations explains why the soils report is not optional.

The order that works

Check the zone and lot size for the address with the city. Read the CC&Rs, especially if you want a detached unit. Decide whether you are building a guesthouse or an ADU, because the code treats them as different uses. Then talk to a designer and a contractor, and only then to a lender. The same sequence applies in the Salt Lake Valley, and building an ADU in Herriman covers how lenders treat the future rent.

In my experience the people happiest with an ADU in St. George built it for a parent or an adult child first and treated any rent as a bonus. I am Kelsey Earl, a Realtor with Keller Williams South Valley, and if you are choosing between houses partly on whether one could take an ADU, send me the addresses and we can check lot size and HOA rules before you write an offer.

Note: General information, not legal advice. City ordinances, state statutes and HOA documents change; confirm the current rules for a specific property with the City of St. George and, for HOA questions, with the association or a Utah real estate attorney before you design or build.