Your family needs more room. Your backyard already has it.

Casita, guest house, ADU — what's the difference?

Legally, nothing. Arizona law calls it an accessory dwelling unit (ADU): a self-contained living space on the same lot as your home, with its own sleeping area and bathroom, and optionally its own kitchen. Around Phoenix, everyone just says casita. Guest house, in-law suite, backyard cottage, pool house with a bathroom — if it's a livable second unit on your property, it's the same thing in the eyes of the city.

It can be detached in the backyard, attached to your home, or converted from an existing garage. This guide focuses on detached casitas — the most popular option for families, because it gives everyone a real front door and real privacy.

Why Arizona families are building casitas right now

The reasons we hear most often from homeowners in Mesa, Phoenix, and across the Valley:

• Aging parents. Mom or Dad stays close — with their own kitchen, their own door, and their own dignity — instead of an assisted-living facility that can run $4,000–$6,000 a month. A casita often pays for itself against just a few years of facility costs.
• Adult kids who need a runway. A college grad saving for their own place, or a young family between homes. Everyone gets space; nobody's sleeping in the den.
• Home office or studio. A real workspace that isn't the kitchen table — and converts to guest quarters or a rental when work changes.
• Guests, without the shuffle. Out-of-state family visits a lot when you live in Arizona. A casita means nobody gives up their bedroom for two weeks every winter.
• Future flexibility. The same casita that houses your father this decade can house a tenant the next. Arizona law now protects your right to rent it long-term (more on that below).

Arizona rewrote the rules in your favor

For decades, building a backyard casita meant zoning variances, public hearings, and neighbors with veto power. Two state laws changed that.

HB 2720 — the "Casita Bill" (cities)

Signed in 2024 and effective January 2025, HB 2720 requires every Arizona city with a population over 75,000 — Phoenix, Mesa, Scottsdale, Tempe, Chandler, Gilbert, Glendale, and more — to allow ADUs by right on single-family lots. That means:

• No special-use permit, no variance, no public hearing. If your lot qualifies, you're entitled to build.
• At least one attached and one detached ADU allowed per single-family lot.
• Cities can't require extra parking just because you're adding a casita.
• Setbacks are capped — cities can't demand more than five feet from side and rear property lines for a single-story unit.
• Cities cannot prohibit you from renting it out long-term, and can't require the occupant to be a relative or employee.

HB 2928 — closing the county gap

Signed May 2025, HB 2928 extends similar rights to unincorporated county land. Counties had until January 1, 2026 to adopt ADU rules; any county that didn't must now allow ADUs on all residentially zoned lots. If your property is outside city limits — parts of the far East Valley, county islands, rural Maricopa — this is the law that applies to you.

Three fine-print items worth knowing

• Historic districts are different. Designated historic neighborhoods (Coronado, Willo, Encanto, and other overlay districts) still go through design review. Buildable — we do it — but the streamlined path doesn't fully apply. Budget more time.
• Your HOA still has a say. State law overrides the city, not your CC&Rs. If you're in an HOA, check the covenants early — some restrict outbuildings or require architectural approval.
• Each city fills in the details. Size caps, height limits, and design standards vary by city within what state law allows. Mesa's rules aren't identical to Phoenix's. This is exactly the kind of thing your builder should know cold.

Will a casita fit on your lot?

The good news: most Phoenix-area single-family lots qualify. Here's the quick self-check:

Beyond square footage, the things that actually determine feasibility are the ones you can't see from the street:

• Utility routing. Where your sewer line runs and whether your electrical panel has capacity are the two biggest cost variables in any casita project.
• Access for construction. A side yard wide enough to get equipment through saves real money versus craning materials over the house.
• Easements. You can't build over a public utility easement without written consent — this kills more backyard plans than any zoning rule.
• Trees, pools, and slopes. Existing site features shape where the unit can go and what site work costs.

All of this is knowable before you spend a dollar. A lot analysis takes us a few days and tells you exactly what you can build and roughly what it'll cost.

What a casita really costs in 2026

Here's the number everyone dances around, so let's not: SOKO builds a 400 SF studio casita starting at $99,000, which includes a $10,000 allowance covering architectural plans and utility connections. City permit fees are the one thing you pay directly — at the city's actual cost, with no builder markup. That works out to roughly $248/SF — and it's worth seeing next to what other Phoenix-area builders publish:

Competitor pricing from publicly published rates as of August 2026; inclusions vary by builder — always compare what's actually in the number. SOKO pricing: construction of the unit plus a $10,000 allowance for plans and utility connections; city permit fees paid by client at cost. Site conditions (trenching distance, panel capacity, sewer depth) can add cost, and we tell you before contract, not after.

SOKO pricing by size

Starting prices include construction plus a $10,000 allowance for architectural plans and utility connections; city permit fees are paid by you at the city's actual cost. Your exact number is confirmed after a free lot review, before you sign anything.

The size trick nobody explains

Cost per square foot drops as the unit gets bigger, because the expensive parts of a casita — kitchen, bathroom, utility connections — cost about the same whether the unit is 400 SF or 900 SF. You can see it in our own pricing: the studio runs ~$248/SF while larger units scale at roughly $180–200/SF. If you're deciding between a 450 SF and a 650 SF unit, the second one costs far less per foot than you'd expect — and the market pattern holds across every builder in the comparison table above.

The 800 SF fee cliff

What moves the price up or down

• Utility runs — a sewer tie-in 20 feet away versus 90 feet away is a real difference. This is why we quote after seeing your lot, not before.
• Electrical panel — if your main panel is maxed out, an upgrade adds cost.
• Finish level — builder-grade to custom finishes is the widest swing in any construction budget.
• Permits and city fees — Phoenix-area permitting typically runs a few thousand dollars, paid directly to the city at cost (we don't mark up permits). Historic districts and oversize units add more.

From "we're thinking about it" to keys in the door

With a design-build firm, one team owns the whole timeline. Here's how a SOKO project actually runs:

1. Lot analysis & feasibility Days, not weeks

   We verify zoning, lot size, setbacks, easements, utility locations, and HOA status. You get a straight answer on what you can build and a realistic budget range — free.

2. Design & plan selection 1–3 weeks

   Start from one of our pre-designed casita plans (fastest, most cost-certain) or customize. Pre-designed plans are how you keep a project near that $99K starting point.

3. Permitting ~60–90 days in most Valley cities

   We prepare and submit the full permit package and handle city review comments. You don't chase the city; we do. Historic overlays and custom designs take longer.

4. Construction ~4–6 months typical

   Site work, foundation, framing, utilities, finishes. Because the ADU is in your backyard, you stay in your home the entire time — this isn't a remodel that displaces your family.

5. Final inspection & move-in Done

   City sign-off, keys, and a housewarming. Total project timeline from first call to move-in typically runs 8–12 months.

How families actually pay for it

Most homeowners don't write a check for the whole project. The most common routes, roughly in order of popularity:

• Home equity line of credit (HELOC). The workhorse. If you've owned your Valley home more than a few years, you likely have significant equity. Flexible draws match how construction billing actually works.
• Cash-out refinance. Replace your mortgage with a larger one and use the difference. Makes the most sense when the new rate is competitive with your current one.
• Renovation/construction loan. Loans that qualify you based on your home's future value with the casita included — useful if your current equity is thin.
• Savings + partial financing. The most common real-world answer is a mix: some cash, some HELOC.

One more thing worth knowing: major mortgage programs now recognize ADU rental income, which can help with qualification if you plan to rent the unit down the road. We're happy to point you to lenders who do ADU projects regularly — ask during your lot analysis.

We're builders, not lenders — treat this as orientation, not financial advice, and talk to a loan officer about your situation.

The five mistakes that cost homeowners the most

• Skipping the feasibility check. Paying for design before anyone verifies easements, sewer routing, and HOA rules is how people buy plans they can't build. Feasibility first, always.
• Comparing quotes that include different things. One builder's "$120K" includes permits, utilities, and appliances; another's doesn't. Make every bidder itemize what's in the number — you'll find the cheap quote usually isn't.
• Designing custom when a pre-designed plan would do. Custom architecture adds months and five figures. If a proven floor plan fits your family, the fastest and cheapest path is the one that's already been permitted before.
• Ignoring the 800 SF fee threshold. Building an 850 SF unit when 795 SF would serve the same purpose means paying impact fees for 55 square feet of drywall.
• Forgetting the HOA until submittal. The city can't stop you; your HOA might slow you down. Pull your CC&Rs in week one, not month four.

What a casita does to your home's value — and your options later

You're building this for family. But it's worth knowing what you're creating financially:

• Appraised value. Finished, permitted living space adds real appraised value — and lenders increasingly value ADUs on their income potential, not just their square footage.
• Rental optionality. Backyard casitas in Phoenix currently rent for roughly $1,400–$2,000/month, based on active and recently closed listings across the metro. The median confirmed casita rental sits around $1,650/month. If life changes and the casita empties out, it becomes an income stream — and state law guarantees your right to rent it long-term.
• Resale story. A home with a permitted casita appeals to three buyer pools at once: multigenerational families, buyers who want income to offset the mortgage, and investors. More demand, better exit.

Find out what your lot allows — free

Tell us where the property is and what you're hoping to build. We'll come back with your lot's zoning status, which state law applies, what size unit fits, and a realistic budget range. No cost, no obligation, no pressure — if a casita doesn't make sense on your lot, we'll tell you that too.

Prefer to talk it through? Call or text us at 480-660-3133 — you'll reach a builder, not a call center.