Finance · 2 min read · April 22, 2026 · 335 words
How much does an ADU add to your home's appraised value?
Appraisers don't always credit an ADU dollar-for-dollar. Here's what actually moves the comp.
Key takeaways
- If you spend a meaningful sum to build an ADU, your home's appraised value will go up — but rarely dollar-for-dollar with build cost.
- How much of the build cost gets credited depends on which valuation method the appraiser uses, and whether the ADU has verified rental income by the time the appraisal happens.
- This guide explains the three valuation approaches appraisers use and how to feed each one.
On this page
If you spend a meaningful sum to build an ADU, your home's appraised value will go up — but rarely dollar-for-dollar with build cost. How much of the build cost gets credited depends on which valuation method the appraiser uses, and whether the ADU has verified rental income by the time the appraisal happens. This guide explains the three valuation approaches appraisers use and how to feed each one.
Sales comparison: the weakest method for ADUs
The default approach looks for recently-sold homes with an ADU in your neighborhood. The problem: ADU-equipped comps are sparse in most markets, so the appraiser falls back to a 'gross living area' adjustment that under-credits a separate, rentable unit. If your appraisal comes in low, ask for the income approach as a secondary support.
Income approach: where ADUs shine
Required by Fannie Mae since 2023 for properties with ADUs producing rental income. The appraiser uses a gross rent multiplier or direct capitalization on the verified rent stream, so the valued contribution depends on the actual rent your ADU commands and the cap rate the appraiser selects for your market. To use this, you need a 12-month lease and bank-deposit records; ask the appraiser which rent figure and cap rate they applied so you can check it against current comparable listings for your neighborhood and unit size.
Cost approach: the floor
Replacement cost minus depreciation. For a 1-year-old ADU this is essentially your build cost. Useful as a sanity floor when the sales comparison comes in unreasonably low.
Sources
- Fannie Mae Selling Guide — ADU appraisal · Fannie Mae
- Appraisal Institute — ADU valuation guidance · Appraisal Institute
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