Building a casita in Surprise: the rules, fees and the math

Surprise is covered by Arizona's 2024 casita law, so an attached and a detached unit are allowed by right on a single-family lot with no owner-occupancy or extra parking requirement. Below is how Surprise wrote that into its own code, read from the city's ordinance on October 7, 2026, and what the resale market here does to the decision.

The rules in Surprise

Ordinance / code	Ordinance 2025-43; Municipal Code Chapter 106, Article XI (Sections 106-11.1 to 106-11.7)
Adopted	December 17, 2024
Units allowed	One attached and one detached per single-family lot of any size; one attached and two detached on an acre or more with an affordable unit. Not on duplex or multifamily lots.
Maximum size	Up to 75% of the main home's gross floor area or 1,000 sq ft, whichever is less.
Larger lots	No size increase. Lots of an acre or more: one attached and two detached if one unit is restricted affordable for 30 years.
Setbacks	The house's setbacks, except rear and side need be no more than 5 ft; front as for the house. Same lot coverage and frontage as the house.
Height	The same height limits as a single-family home in the district.
Parking	No additional parking space or in-lieu fee.
Renting it out	The code defers to the state statute's long-term rental definition and sets no owner-occupancy requirement. We found no ADU-specific short-term rental restriction.
Permit process	Administrative review and approval by the Community Development Director with no hearing, then a building permit. The city must determine an application complete within 30 days (15 days on resubmittal). A denial can be appealed.
Plan review time	Completeness determination within 30 days; substantive review time is not published.

The code as read excludes lots on tribal land or near a military airport (Luke Air Force Base), a general aviation airport or a public airport, which is broader than the 65-decibel standard the state adopted in 2025; parcels near Luke should be checked individually. Surprise adopted the 2024 building codes effective January 1, 2026. Permit, impact and utility fee schedules were not retrievable; fees are confirmed per address.

Source: City of Surprise: Municipal Code Chapter 106, Article XI, Accessory Dwelling Units. Read October 7, 2026.

Fees in Surprise

Surprise does not publish a simple ADU fee figure. Permit fees are set by valuation, impact fees depend on the fee district, and water and sewer fees depend on the provider; we pull the exact numbers for your parcel during the property review.

In June 2026 the state capped the development (impact) fees a city may charge an ADU for services other than water and sewer at the lesser of 25% of the single-family fee or the unit's proportionate share, and limited water and sewer fees to the unit's added demand (HB 2946, signed June 5, 2026). Most cities had not yet re-published schedules when we read them; Glendale's 25% ADU line is the first we found. Expect ADU impact fees to fall toward that cap. Governor's announcement.

What the state law guarantees here

Whatever the local code says, in Surprise these points come from A.R.S. § 9-461.18 and the city cannot be stricter:

At least one attached and one detached ADU on any lot with a single-family home, as a permitted use (no public hearing, no variance)
A unit up to 75% of the main home's gross floor area or 1,000 sq ft, whichever is smaller (cities may allow larger)
A third, detached unit on lots of one acre or more if one unit is deed-restricted affordable
Separate long-term rental of either the house or the ADU (leases of 90 days or more, or month to month)

The math in Surprise

Redfin's median sale price in Surprise is $230 per square foot. A new casita builds for about $265 to $280 per finished foot and a garage conversion for about $120. That puts Surprise in the "Conversion territory" tier: one square foot of new casita, at the typical $272 build cost, comes out −$99 at a 75% appraiser credit and −$42 at full credit. A conversion clears at either credit.

The target areas page explains the tiers and the math page has the calculator. Rent is the other half: see rental math.

Owners and investors in Surprise

Homeowners get a by-right unit for family, guests or long-term rent, with the same appraisal and lender rules as anywhere in the Valley.
Investors can treat the casita as the piece that moves a house out of its neighborhood's price band at resale, as our two Maryvale sales show on the case studies, and as monthly income in the meantime. Surprise's rental rules above say whether both units can be let separately.
Either way the lot decides: setbacks, utilities, sewer depth and easements. Request a property review and we confirm the current Surprise rules for your address.

Other city pages: Phoenix, Mesa, Chandler, Gilbert, Scottsdale, Tempe, Glendale, Peoria, Goodyear, Buckeye.

Rules were read from Surprise's published ordinance and planning material on October 7, 2026 and summarized in plain terms; this is not legal advice. Cities amend codes, and some parcels sit in zones the state law excludes (near military airports, in airport noise zones, on tribal land). We confirm the rules that apply to your parcel during the property review.

Request a property review

Find out what your property can hold.

Send the address and your goal. Anthony Alexander Lopez or Juan M Lopez Solano will review zoning, setbacks and utilities and reach out within one business day. No obligation, and no city approval implied: it is our professional read of your lot.

Prefer to talk? (602) 386-6623 · See completed projects