What drives the complete budget of an ADU

Two casitas of the same size can cost very different amounts. The difference is almost never the finishes. It is the ground, the utilities and the city. Here is the whole budget, bucket by bucket, so you can read any quote with confidence.

The five buckets

Every ADU estimate we write breaks down into the same five parts. When you compare bids, make sure each one covers all five; a low number that leaves out utilities or permits is not a low number.

Bucket	What it covers	What moves it
Design, engineering and permits	Plans, structural engineering where required, energy calculations, permit application and plan-review fees, inspections.	New structure versus conversion; Whether the city requires engineering for your roof or foundation; Plan revisions and review rounds
Building construction and finishes	Foundation or slab work, framing, roofing, insulation, drywall, doors and windows, flooring, cabinets, counters, fixtures, paint.	Square footage; Finish level: builder-grade to custom; Wet rooms: a full kitchen and bath cost more than a kitchenette
Site preparation and access	Demolition, grading, removing concrete or landscaping, protecting the existing home, getting equipment into the yard.	Where the unit sits on the lot; Side-yard access for equipment; Existing slabs, trees, walls or pools in the way
Utility connections or upgrades	Electrical panel capacity or a sub-panel, trenching for water and sewer, gas, HVAC (usually a mini-split).	Distance from the unit to the main panel and sewer line; Age and size of the existing panel; Septic versus city sewer
Optional features and contingency	Covered patio, laundry, upgraded appliances, solar readiness, and a reserve for what opens up once walls come down.	Your wish list; Age of the existing structure for conversions

Why utilities and site work decide the budget

A new unit needs power, water, sewer and usually gas or an all-electric design. If your panel is already at capacity, the unit needs a panel upgrade or a sub-panel. If the sewer line is on the far side of the house, the trench runs further. On a septic lot, the system may need review. None of this shows up in a square-foot price, which is why we check it before quoting.

Site work is the second surprise. Equipment has to reach the build area. Old slabs, mature trees, block walls and pools can all be in the way, and a sloped yard changes the foundation.

Conversions versus new structures

A garage conversion skips the foundation, framing and roof, which are large line items on a detached unit. It adds its own items: correcting slab height or drainage, insulating walls that were never meant to be living space, and closing the garage door opening. It is usually the least expensive path to a livable unit, but it is not free of structure work.

An attached addition sits in the middle. It shares a wall and often utilities with the house, so trenching is short, but it ties into the existing roof and structure, so engineering matters more.

Size and finish level

Size matters, but less than people expect, because kitchens and bathrooms cost roughly the same whether the unit is 400 or 700 square feet. The wet rooms are the expensive rooms. A kitchenette instead of a full kitchen is the single biggest optional saving on most units.

What our estimates include

Included

Permit management from application to final inspection
Licensed trades for electrical, plumbing and HVAC
A written scope with no hidden allowances (see our FAQ)
One-year workmanship warranty, with manufacturer warranties passed through

Not included

Furniture, appliances unless listed in the scope
Impact fees or utility-company charges set by the city or provider
Landscaping beyond what the build disturbs
Financing costs

Why there are no prices here

$We do not publish prices. $Every project is different, and every city in Maricopa County has its own rules, fees and review times. A number on a website would either be wrong for your lot or so wide it means nothing. After a property review and a site visit you get a written, itemized number for your project, with what it includes and what it does not. The fastest way to a real number is a property review followed by a site visit.

How to read a casita quote

Ask which of the five buckets each line belongs to. If one bucket is missing, ask why.
Ask whether permit fees, plan review and engineering are inside the number or "to be determined".
Ask what happens if the panel needs an upgrade or the sewer tie-in runs long. A good quote says who carries that risk.
Ask for the contingency as a separate line, and what triggers using it.
Ask for the warranty in writing.

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