ADU Not Counted in Your Appraisal? Here's Why and What To Do

A friend of mine spent eighteen months building a backyard ADU. Permitted, inspected, rented out for $1,400 a month. When she refinanced, the appraiser barely mentioned it. The value came back far below what she had expected. She called me wondering what went wrong.

ADU valuation is one of the trickiest parts of residential appraisal right now. The short version: appraisers often struggle to value ADUs accurately because there are not enough comparable sales with ADUs in most markets. That is a data problem, and it can cost you real money.

Why ADUs Get Undercounted

Fannie Mae updated its ADU guidelines in 2022 to make it easier for lenders to count ADU rental income and reflect ADU value in appraisals. But the guidelines are only as good as the data available. If your neighborhood does not have many ADU sales, the appraiser has nothing to compare yours to.

The result is often an under-adjustment. The appraiser adds something for the ADU, but not enough. Or they classify the space incorrectly, treating a legal permitted ADU like a storage room or a bonus space.

Check the Report Carefully

Pull your appraisal report and look for how the ADU is described. Is it listed as a legal conforming accessory unit? Or is it described in a way that minimizes it? Check whether the appraiser noted its permit status. Check whether they included any rental income analysis.

If the ADU is permitted and occupied, it should be treated as a legal income-producing unit. If the report does not reflect that, you have an error to dispute.

Finding the Right Comps

The hardest part of an ADU dispute is finding comparable sales. You may need to look at a wider geographic area or at sales from the past twelve months instead of six. If you can find two or three homes with ADUs that sold at prices reflecting that extra unit, you have the foundation of a reconsideration of value.

Check county records, Zillow, Redfin, and any local MLS data you can access. Look for listings that specifically mention "ADU," "in-law suite," "guest house," or "accessory dwelling." Save those addresses and sale prices.

How to Write the Dispute

Your ROV letter should document the ADU clearly. Include its square footage, permit number, year built, and current rental status. Attach the permit documentation if you have it. Then present the comparable sales you found and explain why they are more relevant than what the appraiser used.

Keep the tone factual. You are not attacking the appraiser. You are providing information they may not have had access to.

If you want to make sure you are reading your appraisal correctly and not missing anything, worthmore.ai is built specifically to help homeowners spot these gaps and put together a strong ROV.