An AVM, an automated valuation model that predicts value from property records and nearby sales, misses most of what decides how a permitted ADU affects a Claremont property: whether the unit is in the record at all, where its square footage was counted, whether it was permitted, how it is finished, and what local buyers have paid for similar lots with a second unit. A model cannot open the permit file or walk into the unit. The estimate it produces is an automated estimate, and it is not an appraisal.
This article belongs to the online estimates vs. appraisals series. The general method is in what an automated valuation model is and is not; this page stays with the ADU.
What is a permitted ADU in Claremont?
The City of Claremont describes an accessory dwelling unit, "commonly referred to as a granny flat, back house, or garage conversion," as a residential unit that "provides complete independent living facilities for one or more persons." A junior ADU, in the city's words, "is a unit that is no more than 500 square feet in size" and is "created within the walls of a proposed or existing single-family residence." Applications go through the city's Planning Division, which also offers "three pre-approved plans for the construction of Accessory Dwelling Units."
Permitted means the unit went through that process and was signed off. In Claremont these units can sit behind older houses near the Village and the Colleges, and on the wider lots of the postwar ranch tracts north of Foothill Boulevard, where garage conversions and the permit history on additions already shape the comparison.
Five things an AVM misses on an ADU
1. Whether the unit is in the record at all
An AVM reads the public record, the facts the county holds about a parcel such as recorded building area, lot size, year built and recorded sales, plus whatever listing data it has. A recently finished ADU may not show there yet, or may show as a line with no detail. If the model has no ADU, its number is for a lot with one house.
2. Where the square footage went
Sometimes the unit's area is folded into the house's total. That overstates the main house to the model, and the model then compares it with larger single houses. For loans sold to Fannie Mae, its Selling Guide, section B4-1.3-05, tells appraisers that the living area of an ADU "should not be included with the finished above-grade square footage calculation of the primary dwelling" and that "It should be reported and adjusted for on a separate line in the grid, unless the ADU is contained within or part of the primary dwelling with interior access and above grade." An appraiser keeps the gross living area, the finished, heated space above grade in the main house, apart from the unit. Whether an ADU is part of gross living area covers that measurement in depth.
3. Whether it was permitted
A record line that says "second unit" or "converted garage" does not carry the permit history. A model cannot tell a permitted ADU from a garage conversion done without permits. The appraiser asks for the permit and final sign-off, describes the unit as found, and states in the report how it was treated.
4. What the market pays for it
The question is contributory value, what an improvement adds to the whole property in the market. It is not the construction cost. In any one Claremont pocket there may be few recent sales of houses with a similar second unit, so the appraiser searches for them on purpose and explains the radius and each adjustment. Fannie Mae's guide says that "When there is an ADU, the appraisal report must include a description of the ADU and analysis of any effect it has on the value or marketability of the subject property." A model gives no such analysis. How an ADU is appraised: permits and contributory value walks through it.
5. Finish, condition and layout
Two ADUs of the same size can differ in kitchen, bath, separate entrance, ceiling height and quality of finish. Fannie Mae's eligibility section, B2-3-04, says an ADU "must provide for living, sleeping, cooking, and bathroom facilities." Opendoor says its estimate "may not reflect recent renovations, current condition, or unusual features," and HomeLight says its tool "may not fully account for recent upgrades, additions, or the unique characteristics of your home."
The blank comparable grid, ADU lines
A comparable sale is a closed sale of a similar property that a buyer of the subject would have weighed. In the report the appraiser sets the subject beside its comparable sales line by line. The grid below is blank on purpose: every figure is a dash.
Line in the gridWhat an AVM usually hasSubjectComparable 1Comparable 2Comparable 3
Main house gross living area
A recorded figure, sometimes with the ADU folded in
-
-
-
-
ADU living area, on its own line
Often missing
-
-
-
-
ADU permit status
Not known
-
-
-
-
ADU kitchen, bath and entrance
Not observed
-
-
-
-
ADU condition and quality
Not observed
-
-
-
-
Adjustments and reasoning
None shown
-
-
-
-
The appraiser fills each row from what was seen, measured and documented.
What should a Claremont owner have ready?
- The city permit and final sign-off for the unit, and the approved plans if you have them.
- The date the unit was completed, and any later work on it.
- Access to the unit on inspection day; if it is rented, arrange the tenant's access in advance.
- Notes on utilities, entrance and parking.
The inspection runs 30 to 60 minutes for a standard single-family home, longer for hillside, custom, multi-family or homes with additions. How to prepare for a home appraisal in Claremont lists the rest of the paperwork. If you plan to fix the unit's facts on a portal first, read what correcting home facts changes.
Four numbers that are not appraisals
An automated estimate is not an appraisal. An agent CMA, the comparative market analysis a licensed real estate agent prepares to suggest a list or sale price, is not an appraisal. A county assessment, the taxable value the Los Angeles County Office of the Assessor sets for a Claremont parcel under California's assessment rules, is not an appraisal. A cash offer, the price a buyer will pay on stated terms, is not an appraisal. The appraisal vs. estimate page sets all five side by side, and why three estimators give three numbers explains why a lot with a rear unit often draws a wide spread.
Next step
When someone else will rely on the value of a lot with a permitted unit, new construction and ADU appraisal describes the assignment, and the Claremont area page describes the pockets where these units sit. The pillar, what an online estimate cannot see in Claremont, covers the other blind spots. You can request an appraisal or call (909) 324-6122. The fee is set by the scope of the assignment and quoted before work begins, and it does not depend on the value.
Sources
- City of Claremont, Accessory Dwelling Units (definition of an ADU and a junior ADU; Planning Division application) (accessed November 6, 2026)
- City of Claremont, Accessory Dwelling Units Pre-Approved Designs (accessed November 6, 2026)
- Fannie Mae Selling Guide B4-1.3-05, Improvements Section of the Appraisal Report (06/04/2025) (accessed November 6, 2026)
- Fannie Mae Selling Guide B2-3-04, Special Property Eligibility Considerations (11/04/2026) (accessed November 6, 2026)
- Opendoor, home value estimator (accessed November 6, 2026)
- HomeLight, home value estimator (accessed November 6, 2026)
- Zillow, Zestimate page (attempted November 6, 2026; the page refused automated reading, so it is not quoted)
- Los Angeles County Office of the Assessor (accessed November 6, 2026)
- The Appraisal Foundation, Uniform Standards of Professional Appraisal Practice (USPAP), 2024 edition (accessed November 6, 2026)
- California Bureau of Real Estate Appraisers, license lookup for Gordon Hall (accessed November 6, 2026)
Gordon Hall, California Certified Residential Real Estate Appraiser, BREA No. AR003877 (lookup: https://www2.brea.ca.gov/breasearch/faces/party/view.xhtml?id=23601). Reports are prepared in conformity with the Uniform Standards of Professional Appraisal Practice (USPAP). Nothing here is legal or tax advice; admissibility is always the court's decision.
Frequently asked questions
Does an online estimate include my permitted ADU?
Sometimes, and you usually cannot tell. An automated estimate reads the public record and listing data. A recently finished ADU may not be in the record yet, may appear as a line with no detail, or may have its area folded into the main house. None of these tells the model whether the unit was permitted or how it is finished.
Is an ADU counted in the main house's square footage on an appraisal?
Generally not. For loans sold to Fannie Mae, its Selling Guide section B4-1.3-05 says ADU living area should not be included with the primary dwelling's finished above-grade square footage, and should be reported and adjusted for on a separate line in the grid, unless the ADU is part of the primary dwelling with interior access and above grade.
Is an ADU worth what it cost to build?
Not necessarily. An appraisal measures contributory value, what an improvement adds to the whole property in the market, which is read from sales of comparable properties, not from construction cost. The report describes the unit, analyzes its effect on value or marketability and explains the comparable sales used.
What should I give the appraiser about my Claremont ADU?
The City of Claremont permit and final sign-off, approved plans if you have them, the completion date and any later work, notes on entrance, utilities and parking, and access to the unit on inspection day. If the unit is rented, arrange the tenant's access in advance.
