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

The rules in Mesa

A separate independent entrance is required, with no internal connection to the house. A partial or full kitchen is allowed. Manufactured homes, RVs, trailers and tiny homes on a chassis may not be used as a unit. The 2025 amendment removed ADUs from the detached accessory building size cap.

Source: City of Mesa: Accessory Dwelling Units; library.municode.com; mesaaz.gov. Read October 7, 2026.

Fees in Mesa

• Permit and plan review. Valuation-based residential rate table in the Development Services fee schedule (base fee plus a per-$1,000-of-valuation charge).
• Impact fees. Public safety impact fee of $402 per single-residence dwelling unit under the FY 2025–26 report; other categories are not clearly ADU-applicable and there is no ADU line.
• Utility connection and capacity. Water and wastewater capacity fees per the utility rate book. Separate meters or sub-meters are permitted; the unit must use the same utility providers as the house.

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 Mesa 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 Mesa

Redfin's median sale price in Mesa is $257 per square foot. A new casita builds for about $265 to $280 per finished foot and a garage conversion for about $120. That puts Mesa in the "Conversion territory" tier: one square foot of new casita, at the typical $272 build cost, comes out −$79 at a 75% appraiser credit and −$15 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 Mesa

• 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. Mesa'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 Mesa rules for your address.

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