Homeowner guide
Can you build a casita on your property?
Whether you can build an accessory dwelling is decided by several separate systems. Most guidance blurs them together, which is why the answer so often turns out to be wrong.
Read this first
Four systems, not one.
Most guidance answers “can I build a casita?” as though one rule decided it. Four separate systems do, and they can disagree. State law can require your city to allow something your HOA still prohibits. Your city can permit a unit that building code then forces you to detail differently.
Throughout this guide, each statement is labelled with which system it comes from. When you get an answer from anyone about your property, the useful follow-up question is always the same: which of these four is that answer coming from?
- STATE RULEArizona statute. Sets what covered jurisdictions must allow.
- LOCAL RULEYour city or county's adopted ordinance. The operative rule for your parcel.
- PRIVATE RESTRICTIONHOA declarations and CC&Rs. Independent of every public rule above.
- PROJECT-SPECIFICAnswerable only by looking at the actual property.
Layer one
What Arizona law requires.
Two separate statutes, and which applies depends on whether your parcel sits inside an incorporated city or on unincorporated county land.
Inside a city or town
A.R.S. § 9-461.18 applies to a municipality “with a population of more than seventy-five thousand persons.” Where it applies, the municipality must adopt regulations allowing at least one attached and one detached accessory dwelling unit as a permitted use on lots where a single-family dwelling is allowed.
The statute does not state how that population is determined, so this guide does not tell you whether any particular city is covered — that would be a guess presented as law. Establishing it for your parcel is part of the jurisdiction-specific check, and it matters, because whether the section reaches your city affects both the allowance below and the fallback in subsection (F).
On unincorporated county land
A.R.S. § 11-810.01 covers accessory dwellings on unincorporated land, applies to Arizona counties with no population threshold, and carried a January 1, 2026 adoption deadline.
This is the pathway most guidance omits entirely. If your property is not inside an incorporated city — which includes places like Sun City and Sun City West — this is the section that reaches it, not the municipal one.
The county wording on size is also stronger than the municipal wording, and the difference is worth knowing. Section 11-810.01(B) says a county shall allow each accessory dwelling unit to be at least 75% of the gross floor area of the single-family dwelling or 1,000 square feet, whichever is less — and states expressly that this does not prohibit the county from allowing a larger unit.
What the state provision covers
- STATE RULEThe state-required size allowance
- Under § 9-461.18(A)(3), a covered municipality must adopt regulations allowing an accessory dwelling unit of 75% of the main dwelling's gross floor area, or 1,000 square feet, whichever is less. Read that as the size the state requires the city to accommodate, and not as a statewide maximum. That figure is not a minimum size your ADU must reach — a smaller design may be possible, subject to the applicable local zoning, building-code and property-specific requirements. Whether a particular city permits something larger is a question for that city's adopted rules. On a 1,100 sq ft house, for example, the state-required allowance works out at 825 sq ft.
- STATE RULESetbacks — measured from the property line
- A covered jurisdiction may not require rear or side setbacks greater than five feet from the property line. Read that precisely: it is about the boundary of your lot. It does not say how far the unit must sit from your house — that is a building and fire code question, covered further down.
- STATE RULEParking
- A covered jurisdiction may not require additional parking to accommodate the unit, or a fee in place of it.
- STATE RULEWho may live there
- A covered jurisdiction may not require a familial, marital, employment or other pre-existing relationship between the occupants of the two dwellings.
- STATE RULELong-term rental is protected
- A covered municipality may not prohibit using or advertising either dwelling as separately leased long-term rental housing, which § 9-461.18 defines as a lease of ninety days or longer, or month-to-month. Short-term rental is a different question governed by different statutes — see below.
- STATE RULEBuilding and fire code still apply — with two limits
- Section 9-461.18(D) preserves applicable building codes, fire codes and public health and safety regulations. But it also provides that a municipality may not require an accessory dwelling unit to comply with a commercial building code, or to contain a fire sprinkler.
- STATE RULEUtility easements
- Under § 9-461.18(E), a unit may not be built on top of a current or planned public utility easement unless the property owner receives written consent. Worth knowing early, because an easement can decide where on the lot a unit can physically go.
- STATE RULEOther restrictions
- Height, lot size and coverage requirements may not be more restrictive than those applying to single-family dwellings in the same zoning area. Certain parcels are excluded — including tribal land and land near military or public airports.
A separate question entirely
Renting a casita short-term.
Long-term and short-term rental are governed by different parts of Arizona law, and conflating them is one of the easiest ways to reach a wrong conclusion about what a casita can be used for.
The ADU statute protects long-term rental — a lease of ninety days or longer, or month-to-month. Short-term and vacation rentals are regulated separately: through A.R.S. § 9-500.39 for cities and towns, and A.R.S. § 11-269.17 for unincorporated county areas.
Those short-term-rental statutes contain a provision aimed specifically at properties that have an accessory dwelling unit on them. Both provide that a jurisdiction may require the owner of a vacation rental or short-term rental to reside on the property, where the property contains an ADU and that unit’s certificate of occupancy, certificate of completion or similar final approval was issued on or after September 14, 2024. Where that final approval was issued on or before September 13, 2024, the provision does not apply.
Two details are easy to get wrong, and both matter.
First, the authority attaches to the property, not only to the casita. It is written around a short-term rental on a property that contains a qualifying accessory dwelling unit — so it can be relevant even where the main house is the unit being rented and the casita is not. Do not assume it applies only when the casita itself is the thing advertised.
Second, the date turns on when the accessory dwelling unit received final approval — not when you bought the property, and not when short-term renting began. For a casita being built now, that date is in the future and within the scope of this provision.
And note the word may. These statutes describe what a jurisdiction is permitted to require, not something that automatically applies everywhere. Whether your city or county has actually adopted such a requirement is a separate question, and one worth asking directly.
These statutes set what a jurisdiction may require; your city or county then decides what it actually does require through its own ordinance and permitting. So whether a particular casita can be operated as a short-term rental is a separate, jurisdiction-specific question from whether it can be built — and it is worth answering before design, not after.
Layer two
What your city or county decides.
The state sets what a covered jurisdiction must allow. Your jurisdiction writes the rules you actually build to, and those rules are what a plan reviewer reads. They can be more permissive. They cover things the statute never mentions — design standards, entry placement, driveway and access requirements, landscaping, and how the unit is addressed for utilities and emergency services.
This is why two homeowners a few miles apart get different answers and both are correct. Phoenix, Scottsdale, Chandler, Gilbert and Mesa each run their own review and adopt their own ordinance; they are not interchangeable, and a rule confirmed in one tells you nothing reliable about another.
The practical step is to find your jurisdiction’s current adopted ordinance — not a summary, not a news article, and not this page. Your municipality’s planning or development-services department publishes it, and their counter staff will tell you what applies to a specific parcel.
One caveat worth carrying, though: the adopted ordinance is not automatically the whole answer. Section 9-461.18(F) provides that if a municipality subject to the section failed to adopt the required development regulations on or before January 1, 2025, accessory dwelling units “shall be allowed on all lots or parcels zoned for residential use without limits.” So state law can still be doing work even where a local ordinance is thin or absent, which is another reason a definite answer for a specific parcel comes from your jurisdiction rather than from a general guide.
Read “without limits” carefully, though. It refers to the zoning limits the municipality was supposed to adopt. It does not mean a project is exempt from everything else: subsection (D) preserves applicable building codes, fire codes and public health and safety regulations, subject to the limits stated there, and subsection (E) still protects current and planned public utility easements. Other laws can apply too. The fallback does not waive otherwise applicable permitting, inspection, building-code, fire-code, public-health, safety or utility-easement requirements — it is not a licence for unregulated construction, and it does not tell you what your own property’s pathway will involve.
Layer three
What building and fire code add.
Zoning decides whether a unit is allowed and roughly where. Building and fire code decide how it has to be built — and these are genuinely different questions that get confused constantly.
The clearest example is separation. The five-foot figure in the statute is a setback from your property line. How far the casita must sit from your house, and how walls and openings facing it must be constructed, comes from building and fire code — driven by construction type, fire resistance and opening protection. A design can satisfy every zoning setback and still need to change because of how two structures face each other.
A casita is also a complete dwelling. It needs the same egress, insulation, ventilation, energy compliance and inspection sequence as a house, and it typically ends in a certificate of occupancy. Being small removes none of that.
Layer four
What an HOA can still prevent.
This is the layer most likely to stop a project that everything else permits, and the one almost nobody mentions.
The statutes restrict what a jurisdiction may require. They do not void private agreements between parties. If your property is subject to a declaration or CC&Rs that restrict accessory dwellings, rentals, second kitchens or building placement, those restrictions can still apply — and you agreed to them when you bought.
Read your governing documents, and where an architectural review committee exists, find out what it approves in practice before you pay for design. A homeowner can be entirely compliant with state and local law and still be unable to build.
Layer five
What only your property can answer.
Even when every rule permits a unit, these decide whether it is practical — and they are where budgets move most.
Where utilities come from
Water, sewer or septic and electrical service have to physically reach a detached building — usually by trenching across a finished yard, then restoring it.
Whether your electrical service can carry it
A second dwelling adds load. If the existing panel and service cannot support it, a service upgrade becomes part of the project.
Sewer or septic
Connecting to a municipal sewer is one problem. On septic, an additional dwelling may exceed what the existing system was sized and permitted for.
Site access
A backyard reachable only through a side gate changes how concrete, material and equipment arrive — sometimes deciding where the unit can go at all.
Grade and drainage
Where water currently runs across the site affects the foundation and where a structure can sit without making drainage worse.
Privacy between the two homes
Sight lines, entries and outdoor space are what decide whether the arrangement stays comfortable for everyone living there.
How to get a real answer
For your specific property.
- 01Find out whether your parcel is inside an incorporated city or on unincorporated county land. That determines which statute reaches it.
- 02Get your jurisdiction's current adopted accessory-dwelling ordinance from their planning or development-services department — the ordinance itself, not a summary.
- 03If short-term rental is part of the plan, check that separately. It is governed by different statutes and by your jurisdiction's vacation-rental rules, the owner-residency authority attaches to a property containing a qualifying ADU rather than only to the casita, and it turns on when that unit receives final approval.
- 04Read your HOA declaration and CC&Rs, if any apply. This can end the question regardless of everything else.
- 05Establish where utilities would come from and whether your electrical service can carry a second dwelling.
- 06Only then is it worth paying for design.
Before you rely on this
This is general information about Arizona law as published at the sources below, not legal advice and not a determination about any specific property. Statutes change, jurisdictions adopt and amend their own ordinances, and the rules that govern your parcel are those your municipality or county has currently adopted, together with any private covenants that apply. Short-term rental use is governed by separate state vacation-rental law and local regulation, and requires its own jurisdiction-specific check. Nothing here is a guarantee that an accessory dwelling can be permitted on your property, or operated as any particular kind of rental.
Sources
Check these yourself. Statutes and municipal codes change, and the version your jurisdiction has adopted is the one that governs your property.
- § 9-461.18 — accessory dwelling units (municipalities)Arizona Revised Statutes
- § 11-810.01 — accessory dwelling units (counties)Arizona Revised Statutes
- § 9-500.39 — vacation rentals & short-term rentals (municipalities)Arizona Revised Statutes
- § 11-269.17 — vacation rentals & short-term rentals (counties)Arizona Revised Statutes
- Planning & DevelopmentMaricopa County
Want to know what your lot allows?
Feasibility comes before design. We look at the parcel, the rules that apply to it and where utilities would have to come from — before anyone draws anything.