How Do ADU Appraisals Work?

An ADU appraisal works by having a licensed appraiser evaluate what the finished unit adds to your property’s overall value, looking at its size, its rentability, and how comparable sales in your area have treated similar ADUs. It’s not a simple construction-cost tally. It’s a judgment call grounded in local market data.

The short version: An appraiser weighs your ADU’s square footage, its potential as rental income, and nearby comparable sales to estimate how much value it adds to your property, and that number can vary a fair amount by neighborhood and appraiser.

What the appraiser is actually looking at

Three factors tend to carry the most weight.

Size and usability. A fully permitted, livable ADU with its own kitchen and bathroom reads differently than a small studio or a converted garage. Bigger, more functional units generally support a stronger value add, up to the point of diminishing returns.

Rentability. If the ADU could realistically be rented out, appraisers often factor in that income potential, especially for investment-minded buyers. A unit that’s private, well laid out, and easy to rent tends to appraise more favorably than one that feels like an afterthought.

Comparable sales. This is often the biggest variable. Appraisers look at recent sales of similar properties with ADUs in your area. If ADUs are common and well documented in your market’s sales data, the appraiser has more to work with. If they’re still rare in your specific neighborhood, the appraiser may have to pull comps from farther away or rely more heavily on income-based reasoning instead.

Why the answer isn’t a fixed formula

There’s no statewide multiplier that says “an ADU adds X percent to your home’s value.” Appraisal methodology varies by property, by appraiser, and by how active the local ADU market is. A well-built ADU in a neighborhood full of comparable examples will typically appraise more predictably than one in an area where ADUs are still uncommon.

This is also why the appraisal that matters for your loan or refinance can differ from a rough estimate you might get from an online tool or a real estate agent’s gut sense. If you’re relying on the ADU’s added value for financing, get a real appraisal from a licensed professional rather than assuming a specific number.

For the fuller breakdown, including how ADU appraisals interact with resale value, financing, and what to do if an appraisal comes in lower than expected, see our complete guide: ADU appraisal and resale value.

Where Framework First fits in

The appraisal happens after your ADU is built, but the decisions that shape appraisal value start at design. A well-built, properly permitted unit with a functional layout gives an appraiser more to work with than a bare-bones build. Every Framework First model comes with a project price from $180,000 to $557,000 that builds in a permitting budget along with plans, foundation, the factory build, delivery, utility hookups, appliances, and final inspection. Exact permit costs are set by your city and get confirmed in your feasibility study, so what you build is a fully finished, appraisal-ready unit from day one.

If you’re weighing whether an ADU pencils out for your property, a feasibility study is the right starting point. It looks at your specific lot before you commit to a model.

Frequently asked questions

Does a bigger ADU always mean a bigger value add?

Not necessarily on a straight line. Bigger, more functional units generally support more value, but there’s a point of diminishing returns where added square footage stops moving the appraisal much. An appraiser weighs size alongside usability and how it compares to similar units that have actually sold nearby.

Can I get an accurate appraisal estimate before I build?

Not a formal one. A licensed appraiser typically appraises the completed, permitted unit, since comparable sales data and usability are part of the evaluation. Before building, a feasibility study is a better tool. It looks at what’s buildable on your specific lot, which is a different question than what a finished ADU will appraise for.

Does a rented ADU appraise higher than a vacant one?

Rentability itself, not necessarily current occupancy, is often what appraisers factor in. A unit that’s private, well laid out, and realistically rentable can support a stronger value add than one that isn’t, whether or not it happens to have a tenant in it at the moment of appraisal.

Why would two similar ADUs appraise differently in different cities?

Because comparable sales data drives so much of the process. In an area where ADUs are common and well documented in recent sales, an appraiser has solid comps to work from. In an area where ADUs are still rare, the appraiser may have less direct data and more room for judgment, which can produce a wider range of outcomes for otherwise similar units.

Where can I read more about ADU appraisals and resale value?

Our full guide, ADU appraisal and resale value, covers the deeper mechanics, including how appraised value interacts with financing and resale, and what your options are if an appraisal comes in lower than you expected.

---

Curious what your lot could support? Start with a feasibility study or browse our ADU models to see what fits your budget.