Building a guest house or an Accessory Dwelling Unit (ADU) within the city limits of Tucson involves a number of legal and practical considerations. Here’s an overview of what’s involved, the limitations, and what the law currently allows.
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Guest House vs. ADU: What’s the Difference?
In Tucson, there is a distinction between a guest house and an accessory dwelling unit (commonly called a casita). The key difference is the presence of a kitchen.
A guest house is a detached structure that can include sleeping and bathroom facilities, but it cannot include a kitchen. This means no stove or oven and no full cooking capabilities. A wet bar or mini fridge is typically allowed, but anything that supports independent living is not.
An ADU, on the other hand, is a separate housing unit. It can include a full kitchen, making it suitable for long-term independent living. ADUs are permitted under city law and can be rented out, unlike guest houses.
Legal Requirements and Zoning Rules
If you are building either a guest house or an ADU, your property must meet certain zoning and lot size requirements.
For a guest house:
Your property must be zoned to allow single-family residential use.
The lot typically must be at least 4,000 square feet in area.
You are allowed only one guest house per lot.
It must be located at least three feet away from the main house and meet all setback requirements (how far it must be from the property lines).
It must share the same utility connections (water, electric, etc.) and access point (driveway) as the main house.
It cannot be rented out or used as an independent living unit. It’s strictly for non-paying guests or family members.
For an ADU:
You may build one ADU per residential lot, provided it meets zoning code.
The size of the ADU is limited to 1,000 square feet or 10% of the lot size, whichever is less—but never less than 650 square feet on most lots.
The height of the unit may not exceed 12 feet, or the height of the main house on two-story properties.
ADUs must be placed at least 5 feet from the rear and side property lines.
In most cases, you must provide one off-street parking space, but this requirement can be waived if you’re close to public transit or other qualifying factors.
The ADU must be built on a permanent foundation—tiny homes on wheels or RVs don’t qualify.
The unit must use a “cool roof” material, which reflects more sunlight and helps reduce energy use, in accordance with Tucson’s climate goals.
ADUs can be rented, though typically only for long-term leases (30 days or more, depending on local and state rules).
Permits and Process
All new structures—including guest houses and ADUs—require a permit from the City of Tucson’s Planning & Development Services Department.
You’ll need to submit building plans through the city’s Tucson Development Center (TDC) Online.
Your plans will be reviewed for compliance with zoning laws, building safety, fire codes, floodplain restrictions, and more.
Detached structures larger than 200 square feet require full architectural drawings.
Once approved, construction must be completed by licensed contractors or under owner-builder provisions.
Fees and Costs
When building an ADU, you may be subject to impact fees, which are one-time charges for the infrastructure costs associated with the new dwelling unit. As of 2025:
A smaller ADU (up to 750 square feet) incurs around $2,750 in impact fees.
A larger unit (up to 1,000 square feet) may cost around $4,300.
There are also normal permitting and inspection fees. However, Tucson has programs that provide grants or financial assistance to qualifying homeowners—particularly low-income residents or those converting existing structures into legal ADUs.
State Law Considerations
In 2024, Arizona passed a law (HB 2720) that ensures cities cannot unreasonably restrict ADUs on single-family lots. Under this law:
Cities must allow at least one ADU per residential property.
Local regulations cannot be more restrictive than those applied to the main house in terms of setbacks, height, or lot coverage.
Cities may not prohibit kitchens, unless the structure is intended as a non-rentable guest house.
This means Tucson’s ADU ordinance must conform to this state law. However, cities can still enforce design guidelines, permit rules, and building code requirements.
Neighborhood and HOA Restrictions
Even if the City of Tucson allows an ADU or guest house on your property, you still need to consider any homeowners’ association (HOA) rules or deed restrictions. Many neighborhoods have private covenants that may forbid secondary structures, limit rentals, or require approval for architectural changes.
These rules are enforceable independently of city or state law, so always review your CC&Rs (covenants, conditions & restrictions) if you live in an HOA.
Final Notes
Guest houses are simpler but limited in use and cannot be rented.
ADUs offer more flexibility and rental income potential but are subject to more regulations and higher costs.
The city’s ADU pilot ordinance currently runs through 2026, but all approved ADUs built before that will remain legal, even if the law changes later.
Each property is unique. It’s highly recommended to verify your parcel’s zoning, lot size, and neighborhood overlay status before beginning design or permitting.