Yes, you can build a detached ADU or a guest house on most single-family lots in Scottsdale, and since late 2025 the city has clear, by-right rules for doing it. The catch is that an ADU, a guest house, and a casita are not the same thing under Scottsdale's code, and which one you build decides whether you can rent it, how big it can be, and how it hooks up to utilities.
The short version:
- An ADU (accessory dwelling unit) is a full, independent living space with its own kitchen and entrance. Scottsdale now allows one attached and one detached ADU on a single-family lot by right.
- A guest house is a detached room or suite for your guests. It is not a separate dwelling, it shares utilities with the main home, and it may not be rented on its own.
- A casita is a local nickname, not a legal category. Depending on its kitchen and how it is used, a casita is treated as either an ADU or a guest house.
- Scottsdale caps the first ADU at 1,000 square feet or 75% of the main home, whichever is less. Guest houses are capped at 50% of the main residence combined.
- Expect a detached build in the Scottsdale area to run roughly $200 to $400 per square foot from sourced estimates, higher than the Phoenix average. Confirm every number with itemized bids.
This guide covers what you can legally build, the City of Scottsdale rules, what it costs, and how long it takes. For plan layouts, see our detached casita floor plans for Arizona. This post is the rules and process decision guide.
ADU, guest house, or casita: what is the difference in Scottsdale?
People use all three words for "the extra building out back," but Scottsdale's zoning code draws hard lines between them, and the line changes what you are allowed to do.
ADU (accessory dwelling unit). A self-contained home: kitchen, bathroom, sleeping area, its own exterior entrance, and its own address. It can be attached to the main house or stand alone. Because it is a true dwelling, an ADU is the only one of the three you can rent out as independent housing.
Guest house. The City of Scottsdale defines a guest house as "a detached, subordinate, accessory building used to accommodate guest of the occupants" of the main single-family residence. It is expressly not a dwelling unit or an ADU. A guest house shares utilities with the main home and may not be rented separately from it.
Casita. This is the Arizona vernacular term. It has no standalone legal meaning. A casita with a full kitchen that someone could live in and rent is, under the code, an ADU. A casita built only to host guests, with no independent rental use, is a guest house. Before you design one, decide which legal category you actually want, because that choice drives everything else.
The practical test: if you want rental income or a truly independent living space, you are building an ADU. If you want extra room for family and guests and do not need to rent it out, a guest house is simpler and faces fewer requirements.
Can you build an ADU or guest house on your Scottsdale lot?
In most cases, yes. Scottsdale adopted Ordinance 4687 on September 30, 2025 to bring its code in line with Arizona's statewide ADU law, which took effect January 1, 2025 and applies to cities over 75,000 people (codified at A.R.S. section 9-461.18). The result is that ADUs are now allowed by right, through an administrative review, on lots where a single-family home is permitted.
How many you can build in Scottsdale:
- One attached ADU and one detached ADU per single-family property.
- A third detached ADU is allowed on lots of one acre or more if at least one of the ADUs is a qualifying affordable housing unit.
- Guest houses have no numeric cap, but their combined floor area is limited (see below).
Two things that can still stop you even when zoning allows it: a recorded HOA or CC&R restriction can prohibit ADUs on your lot, and utility easements limit where you can place a structure. Check your HOA documents and your plat before you design anything.
Unsure whether your parcel qualifies or where it can go? Our guide to lot setbacks in Arizona explains how the buildable envelope is drawn, and a builder can pull your zoning and easements in a site review.
What are the City of Scottsdale ADU rules?
Here are the core standards from the City of Scottsdale's accessory dwelling unit page (scottsdaleaz.gov). Verify current figures with Planning and Development before you design, because ordinances are amended.
Size: - The first ADU is capped at 1,000 square feet or 75% of the main home's size, whichever is smaller. - Any additional ADU is capped at 500 square feet.
Setbacks and spacing: - An attached ADU follows the main house's setbacks for its zoning district. - A detached ADU may not sit in a required front or side yard. - A detached ADU in the rear yard may be placed as close as 5 feet to a side or rear property line. - There must be at least 10 feet between the ADU and the main home.
Height: follows the underlying zoning district's maximum.
Private open space: each ADU needs its own outdoor area, a minimum of 5 feet deep and 50 square feet.
Occupancy: no more than six adults in total may live across the main home and all ADUs on the lot combined.
Owner-occupancy and rentals: an ADU may be used as a long-term or short-term rental only if the property owner lives on the premises. This is the rule most buyers miss. You cannot buy a Scottsdale lot, build an ADU, and run it as a standalone rental if you do not live there.
Utilities: each ADU needs separately metered electric and gas, with water and sewer branched from the existing tap on private property. It also needs its own entrance and a visible, unique address. ADUs cannot be sold separately or split off through a lot subdivision.
The permit path is administrative, not a public hearing: an online pre-application, a pre-application meeting with city staff, a formal administrative application for approval, then construction-document permit review. See our walkthrough of custom home building permits for how Scottsdale review works in practice.
How is a Scottsdale guest house different from an ADU?
If you only want space for visiting family, a guest house is the lighter path. The trade-offs, from the City of Scottsdale guest house page:
- Size: combined gross floor area of all guest houses on a property cannot exceed one-half the main residence's floor area. (An ADU can be up to 75% or 1,000 square feet.)
- Detached only: a guest house must be detached. An ADU can be attached or detached.
- No separate rental: a guest house "may not be rented separately from the main single-family residence." An ADU can be rented if the owner lives on site.
- Shared utilities: a guest house shares utilities with the main home. An ADU must be separately metered, which is a real cost difference.
- Deed restriction: a guest house built after January 1, 2025 must be restricted to guest-house use through a private deed restriction recorded before permit approval.
In short, a guest house is cheaper and simpler but legally limited to hosting. An ADU costs more to build and meter but gives you independent and potentially income-producing space. Pick based on how you will actually use it.
What about unincorporated Maricopa County?
If your lot is outside Scottsdale's city limits in unincorporated Maricopa County, county zoning applies instead. In December 2025 the Maricopa County Board of Supervisors approved a new zoning ordinance that allows accessory dwelling units in line with the state mandate, replacing the older county code. The size, setback, and parking specifics differ from Scottsdale's, so confirm them directly with Maricopa County Planning and Development (maricopa.gov) for your parcel. Most of metro Phoenix sits inside a city, so for Scottsdale addresses the city rules above are the ones that govern.
What does it cost to build an ADU or guest house in the Scottsdale area?
Published estimates for a new detached unit in the Scottsdale and Phoenix area generally land at $200 to $400 per square foot, which puts a typical detached casita somewhere around $150,000 to $320,000 all in. A few factors push Scottsdale toward the top of that range:
- Scottsdale premium: local cost guides put Scottsdale roughly 20% to 30% above the Phoenix metro average.
- Separate metering: an ADU's required separate electric and gas connections can add roughly $8,000 to $15,000 that a guest house, sharing utilities, avoids.
- Finish level and kitchen: a full kitchen and higher finishes move the number up fast.
- Site conditions: caliche soil, grading, and utility runs across the lot all add cost.
City permit fees are a smaller line item, reported in the range of $1,800 to $2,550 for a 500 to 1,000 square foot unit. These figures are sourced from contractor and vendor cost guides and are estimates only. For a real budget, get itemized bids and read our guides on what a custom home costs in Arizona and how to get an accurate custom home estimate.
[[OWNER-CONFIRM]] David: does BQB publish a typical price-per-square-foot range or starting budget for a Scottsdale-area ADU or guest house, and does BQB offer a fixed menu of pre-approved casita plans at a set price? If so, we can state real BQB numbers here instead of only the sourced ranges above.
How long does it take, and can it attach to a main-home build?
Timeline depends on whether the ADU stands alone or rides along with a new main home.
Built with a new main home. If you are already building a custom home, folding a detached ADU or guest house into the same set of plans is the most efficient route. One design phase, one permit submittal, one mobilization of crews and utilities. It adds to the overall schedule but far less than doing it as a separate project later.
Built as a standalone addition. On an existing lot, the clock runs through the city's administrative steps: pre-application, pre-application meeting, administrative approval, then construction-document permit review, followed by the build itself. Design and permitting typically take a few months before ground breaks, and build time runs from there depending on size and finishes. Caliche, utility hookups, and change orders are the usual delay drivers in the Valley.
One way to compress the build window is the structural system. We build with steel structural insulated panels (AirLight panels), which arrive engineered and go up faster than site-framing a small structure. That shortens the framing phase on a compact footprint like an ADU.
[[OWNER-CONFIRM]] David: what start-to-finish timeline does BQB commit to for a detached ADU or guest house in Scottsdale, standalone versus bundled with a main-home build? We are describing general phases only and have not stated a BQB-guaranteed duration.
How do you decide which one to build?
Run your situation through three questions:
- Will you rent it or house an independent occupant? If yes, you need an ADU, and you must live on the property to rent it. If it is only for guests, a guest house is simpler and cheaper.
- How big do you need it? Up to 1,000 square feet or 75% of your home points to an ADU. Under 50% of your home and purely for guests fits a guest house.
- Standalone or part of a bigger build? If you are planning a new custom home anyway, design the extra unit into the same plans from the start.
Whatever you choose, the lot, the zoning, the setbacks, and the utilities need to be checked before you fall in love with a floor plan. A builder who knows Scottsdale's process can tell you in a short site review exactly what your parcel allows.
Thinking about an ADU, guest house, or casita on your Scottsdale property? See how we approach custom work as a Scottsdale custom home builder, and browse detached casita floor plans for layout ideas.
FAQ
Is a casita the same as an ADU in Scottsdale?
Not necessarily. "Casita" is a local nickname with no legal definition. If the casita has a full kitchen and could be lived in or rented, Scottsdale treats it as an ADU. If it is only for guests and cannot be rented separately, it is a guest house. The classification controls the rules you must follow.
Can you rent out an ADU in Scottsdale?
Yes, but only if the property owner lives on the premises. Scottsdale allows an ADU to be used as a long-term or short-term rental solely when the owner resides at the property. You cannot build an ADU on a lot where you do not live and run it as a standalone rental.
How big can a guest house be in Scottsdale?
The combined gross floor area of all guest houses on a property cannot exceed one-half of the main residence's floor area. By contrast, a first ADU can be up to 1,000 square feet or 75% of the main home, whichever is smaller.
How many ADUs can I have on one Scottsdale lot?
One attached ADU and one detached ADU per single-family property. A third detached ADU is allowed on lots of one acre or more if at least one of the units is a qualifying affordable housing unit.
What are the setbacks for a detached ADU in Scottsdale?
A detached ADU may not sit in a required front or side yard. In the rear yard it may be as close as 5 feet to a side or rear property line, and it must be at least 10 feet from the main home. Height follows the underlying zoning district.
How much does it cost to build a casita in the Scottsdale area?
Sourced cost guides put new detached units at roughly $200 to $400 per square foot, or about $150,000 to $320,000 all in, with Scottsdale running 20% to 30% above the Phoenix average. An ADU's required separate utility metering can add $8,000 to $15,000 over a guest house. These are estimates; get itemized bids for a real number.
Last updated: October 29, 2026. Rules summarized from the City of Scottsdale accessory dwelling unit and guest house pages (scottsdaleaz.gov), Arizona A.R.S. section 9-461.18, and Maricopa County Planning and Development (maricopa.gov). Verify current figures with the city or county before you design or buy. This article is general information, not legal or professional advice.