Where a new casita clears its cost: the target areas

How the tiers are set

The margin column in each table is the value added minus the cost for one square foot of new casita, at the typical build cost of $272: first at a 75% credit, then at full credit. Multiply by your unit's square footage. Fees, financing and site conditions are not included; the math page covers those.

Clears even at a discounted appraisal (10 areas)

Resale is at least $374 per square foot, so a new casita beats the top of the build range even if the appraiser credits only 75% of the main-house rate. These are the areas where the resale case alone carries the project.

Clears at full credit (10 areas)

Resale is at least $280 per square foot, above the top of the build range. A new casita adds more than it costs when the appraiser credits the space at the full rate; at a 75% credit it falls short, and rent or the casita-home premium has to make up the difference.

At the line (5 areas)

Resale sits inside the $265 to $280 build range. New construction is a coin flip on resale alone; a conversion, or a lot in the pricier part of the area, decides it.

Conversion territory (15 areas)

Resale is below the build cost of new construction. A garage conversion at about $120 per square foot still clears easily (it needs only $160 per foot at a 75% credit). A new casita here is a rental or family decision first, and a resale decision second.

About Maryvale, where we have renovated and sold

Maryvale's median of $221 per square foot puts it in conversion territory on paper. Our own sale there says the paper understates it: 3802 N 48th Dr, a 1956 home with a converted-garage studio, sold in July 2025 for $399,000 on the 1,289 square feet the appraiser counted, which is $310 per counted foot, 40% above the neighborhood median and above the cost to build new. One sale is not a statistic, but it is the pattern we would expect: a complete, permitted unit moves a West Phoenix home out of the neighborhood's price band. In Maryvale and the areas like it, the conversion is the sure thing and the new build is the upside case. The case study has the record.

How to read your own address

1. Find your area above, or look up your neighborhood's median sale price per square foot on Redfin; the city median hides a wide spread.
2. If it is above $280, a new casita is created below market value. If it is above $374, that holds even with a cautious appraiser.
3. If it is below $265, start with the garage if you have one. Then run the rental math; rent carries a new unit in every area on this page.
4. Whatever the tier, the lot decides: setbacks, utilities, sewer depth and easements. That is the property review.