The listing photo shows a separate little building at the back of the lot with its own front door. The remarks call it a casita. The county record says the house is 3,100 square feet. The builder's published floor plan says 2,780. Somewhere in that gap is a room you may or may not legally own the way you think you do.
Casitas and guest suites are one of the features buyers ask me about most in North Peoria, Vistancia, WestWing Mountain, Sonoran Mountain Ranch, and the acre-plus pockets out toward Lake Pleasant Parkway. They also carry more paperwork than almost any other feature a West Valley home can have — and the rules changed recently enough that a lot of what people believe about them is now out of date. Here is what actually governs that second structure, in the order you should check it.
Casita, guest house, guest suite, ADU — these are not interchangeable words
In everyday West Valley conversation, all four terms get used for the same thing. In a zoning ordinance and on an appraisal they mean different things, and the difference decides what you can do with the space.
- Accessory dwelling unit (ADU). Under the City of Peoria, Arizona zoning ordinance, a self-contained living unit on the same lot as a single-family dwelling that is larger than the ADU, with its own sleeping and sanitation facilities, and that may include its own kitchen facilities.
- Guest house / servant's quarters. Peoria still carries these as a separate permitted accessory use in the larger-lot R1-35 and R1-18 residential districts, subject to accessory-building yard requirements.
- Accessory building. A detached secondary structure — pool house, shed, workshop, detached garage. Peoria's code expressly says accessory buildings do not include ADUs.
- Attached guest suite / next-gen wing. Often a bedroom-and-bath suite with a private exterior door inside the main structure. Whether it counts as an ADU depends on the facilities inside it, not what the builder named it.
Don't take the word in the listing at face value. Ask what the permit says the structure is.
What Arizona changed in 2024, and what Peoria adopted that December
Arizona House Bill 2720, signed in 2024 and codified at A.R.S. § 9-461.18, requires municipalities over 75,000 in population to adopt regulations allowing accessory dwelling units on any lot where a single-family dwelling is allowed. Cities had until January 1, 2025 — and the statute provided that a city failing to adopt rules would have ADUs allowed on all residentially zoned lots without local limits. Peoria adopted its version on December 17, 2024 through Ordinance 2024-20, creating Section 21-316 of the zoning ordinance, which states that where its provisions conflict with A.R.S. § 9-461.18, the state law controls.
The state law also limits what cities can't do. A municipality may not require a familial, marital, employment, or other preexisting relationship between the occupant of the main house and the occupant of the ADU. It may not require additional off-street parking, force the ADU's exterior to match the main house, or set rear or side setbacks more than five feet from the property line. Peoria's Section 21-316 mirrors all of that.
Verify the current ordinance with the City of Peoria before relying on any of this for a specific property — codes get amended, and other West Valley cities adopted their own ADU sections with their own details.
The number that surprises people: 75 percent, or 1,000 square feet, whichever is less
This is the most misunderstood rule, and it works against the intuition most buyers bring to it. Under Section 21-316, an ADU may not exceed 75 percent of the gross floor area of the existing single-family dwelling, or 1,000 square feet — whichever is smaller. Gross floor area means interior habitable area.
On a 2,400-square-foot home, 75 percent would be 1,800 square feet, but the 1,000-square-foot ceiling governs. On a 1,200-square-foot home, the 75 percent figure is 900 square feet, and that governs. The cap is always the lower of the two.
Peoria also permits, as of right, no more than one attached and one detached ADU on a single-family lot. On a lot of one acre or more, the city allows one attached and up to two detached — but only if at least one of the detached units is a restricted-affordable dwelling unit, documented through a deed restriction or a development agreement with the city and rented to households earning up to 80 percent of area median income. That provision comes up more often than you'd expect in the Waddell and north Peoria acre-plus corridor.
The unpermitted casita problem — and the date that decides it
This is where West Valley deals get complicated, especially on homes built in the early 2000s where a previous owner enclosed a ramada, converted a detached garage, or added a kitchenette to a pool house without pulling a permit. Peoria built two legalization pathways into Ordinance 2024-20, and each has its own cutoff date:
- Unpermitted accessory dwelling units that were constructed or otherwise in existence prior to September 15, 2024 may apply for a building permit to legalize the unit, subject to Section 21-316, the building standards code in effect at the time of application, and any rules adopted by City Council resolution.
- Unpermitted accessory buildings — the non-dwelling category — that were in existence prior to January 1, 2024 may apply for a permit to legalize the structure under the same general approach.
Two things to understand there. "May apply to legalize" is not the same as "is legal" — it's a door, not a certificate. And legalization is judged against the current building code, not the code that existed when the work was done, which is why an old unpermitted conversion can turn into an electrical, egress, or setback problem after you own it.
If a listing describes a casita and you can't find a corresponding permit, treat that as a real contingency item. Pull the permit history from the city's development services records and compare it against the Maricopa County Assessor's square footage for the parcel. When those two disagree, the gap is usually the story.
What your lender and appraiser actually see
Financing is where a casita either adds measurable value or quietly does nothing at all. Fannie Mae's Selling Guide (section B4-1.3-05) treats an ADU as an additional living area, independent of the primary dwelling, providing facilities for living, sleeping, cooking, and bathroom use on the same parcel. Access matters: the unit must be reachable without going through the primary residence, and there must be some expectation of privacy from it.
Cooking facilities carry more weight than most buyers expect. Industry guidance on these standards holds that a kitchen area needs a stove or a stove hookup — a hotplate, microwave, or toaster oven is not treated as a substitute. That one detail can change how a space is classified, which changes how it's appraised, which can change your loan.
Note the mismatch: Peoria's ordinance says an ADU may include kitchen facilities, while a lender may require them for the space to count as one. Financing guidance on ADUs has also been actively evolving, so confirm current requirements with your lender for your specific loan product and property.
Your HOA can still say no
This is the part that catches West Valley buyers most often, because it runs against the headline everyone remembers about the state law. HB 2720 restricted what cities can do. It expressly allows restrictive covenants concerning accessory dwelling units between private parties, and bars a city from conditioning a permit on whether such a covenant exists. Your city may permit an ADU as of right while your community's CC&Rs prohibit one, limit its use, or require architectural committee approval.
In master-planned West Valley communities, that architectural review layer is real and enforced. Before you write an offer on a home where the casita is part of the reason you want it — or where you plan to add one later — read the CC&Rs and architectural guidelines, not just the fee schedule. Ask whether ADUs are addressed, whether separate leasing is addressed, and what the approval process looks like.
Renting it out: what's protected and what isn't
The state law protects long-term rental. A city may not prohibit the use or advertisement of the single-family dwelling or the ADU on the same lot as separately leased long-term rental housing. Peoria defines long-term rental as a lease of ninety days or longer, or month-to-month.
What that protection does not do is override HOA covenants, override a lender's occupancy requirements, or settle short-term rental questions, which sit under different rules. Section 21-316 is also explicit that an ADU cannot be sold or conveyed separately from the primary dwelling — it isn't a second parcel you can split off later — and it bars using a mobile home, RV, or other movable habitable space as an ADU.
If rental income is part of your math on the purchase, verify all three layers — city, HOA, and lender — before that income makes it into your budget.
The casita verification checklist
Work this list during your inspection period, before your contingencies expire:
- Permit history. Pull the city's building permit records for the parcel and confirm what the structure was permitted as.
- Assessor comparison. Reconcile the permitted square footage against the Maricopa County Assessor record and the listing's stated square footage.
- Certificate of occupancy. Ask whether one exists for the unit, separate from the main house.
- Size math. Compare the unit's interior habitable area to 75 percent of the main house's gross floor area and to the 1,000-square-foot ceiling.
- Setbacks and easements. Confirm distance from side and rear property lines, and that it doesn't sit on a public utility easement.
- Access and privacy. Confirm the unit can be entered without going through the main house.
- Kitchen facilities. Note whether there's a stove or stove hookup, and tell your lender exactly what's there.
- Utilities. Determine whether it's on separate meters or shares the main house's service, and whether panel capacity supports it.
- CC&Rs. Read the recorded covenants and architectural guidelines for ADU and separate-leasing language.
- Insurance. Confirm with your carrier that the structure and any tenancy are covered under the policy you're quoting.
- Lender classification. Ask your loan officer in writing how the unit will be treated for your specific product.
- Inspection scope. Have the casita inspected as a separate structure — plumbing, electrical, HVAC, roof, and egress.
A North Peoria example
Here's an illustrative scenario that reflects how these come up. A move-up buyer touring a home in the Sonoran Mountain Ranch area finds a 640-square-foot detached casita with a full bath, a sink, and a mini-fridge — no stove. The seller's disclosure calls it a guest house built by a prior owner. There's a permit on file for a detached accessory building, but nothing showing a dwelling unit.
Three things follow. Without cooking facilities the unit likely isn't an ADU under the lender's definition, so it probably won't be appraised as one. Because it predates September 15, 2024, there may be a path to apply for a permit to legalize it — subject to today's building code. And whether it can be leased separately is a CC&R question that has nothing to do with either of the first two.
None of that is a reason to walk away. It's a reason to price it accurately and do the verification inside the inspection period instead of discovering it in year two. A casita is one of the most useful features a West Valley home can have — and the one where marketing language and legal reality drift furthest apart. Treat the second structure as its own small transaction: its own permits, its own inspection, its own appraisal question, its own covenants.
Because prices, inventory, zoning ordinances, HOA rules, taxes, insurance, and lending guidelines can change, you should verify the details for the specific property you are considering.
Ready to compare your options? Schedule a friendly consultation with Stephanie White so you can build a simple, step-by-step plan for your next move.
Frequently asked questions
Does a casita automatically add square footage to a home's value in Peoria?
No. Whether it contributes value depends on how the appraiser classifies it — which turns on permits, access, and facilities, not on how the listing describes it. Ask your lender and appraiser how the specific structure will be handled.
How big can a casita be on a Peoria lot?
Under Peoria's zoning ordinance Section 21-316, an ADU is capped at 75 percent of the gross floor area of the existing single-family dwelling, or 1,000 square feet, whichever is less. Confirm the current ordinance language with the City of Peoria before designing or pricing anything.
Can I add a casita to a home I already own in a West Valley HOA community?
Possibly, but two approvals are involved. City zoning is one layer; your community's recorded CC&Rs and architectural guidelines are a separate one, and state law expressly allows private restrictive covenants about ADUs. Check both before committing to plans.
What happens if the casita was built without a permit?
Peoria's ordinance provides that owners of unpermitted ADUs in existence prior to September 15, 2024 may apply for a building permit to legalize the unit, subject to the current building standards code. That's an application pathway, not a guarantee, and the work has to meet today's code.
Can I rent out a casita separately from the main house?
State law bars cities from prohibiting the use or advertisement of the main dwelling or the ADU as separately leased long-term rental housing — Peoria defines long-term as ninety days or longer, or month-to-month. That doesn't override HOA covenants, lender occupancy requirements, or short-term rental rules. Verify all three.
Can a casita be sold separately from the main house later?
Not in Peoria. Section 21-316 prohibits ADUs from being sold or otherwise conveyed separately from the primary dwelling. A lot containing an ADU also can't simply be split without meeting the city's zoning and subdivision requirements, including separate utility service for each unit.
Stephanie White, REALTOR® | Howe Realty
