Does an ADU increase property value?

Does an ADU increase property value?

In California, homes with ADUs appraise for more. Federal Housing Finance Agency data on appraisals for Fannie Mae and Freddie Mac purchase loans put the 2023 median at $1,064,000 for homes with an ADU, against $715,000 for homes without one. From 2013 to 2023, values for homes with ADUs grew 9.34% a year, compared with 7.65%.

That gap isn't the value an ADU adds. Homes with ADUs tend to sit on bigger lots in pricier areas, and FHFA itself says the faster growth “requires further analysis.” What the data does show is that buyers and lenders in California deal with ADUs every day: 2.9% of the state's purchase appraisals in 2023 included one. For the full appraisal and listing picture, see what an ADU means in real estate.

Whether your ADU adds value comes down to two things: whether it's legal, and whether nearby buyers have paid more for homes with one. Freddie Mac tells appraisers that if the comparable sales show no market reaction to ADUs, they may give the unit no value. They can't ignore it, though: skipping an ADU just because there are no sales to compare is “an unacceptable appraisal practice.”

How much does an ADU add to property value?

There's no fixed percentage. Appraisers and owners use three methods, and they rarely agree.

• Comparable sales. This is the method that counts for a mortgage. Fannie Mae has appraisers report a detached ADU on its own line rather than adding its square footage to the house, then adjust for it based on what similar homes with ADUs sold for. Freddie Mac requires at least one comparable sale with an ADU for a zoning-compliant unit, using an older sale or a nearby market if nothing recent exists.
• Income. What the unit could rent for, turned into a value. Fannie Mae requires the income approach only for two- to four-unit properties, and says it may suit one-unit neighborhoods with a substantial rental market. It never accepts an appraisal that relies on income alone.
• Cost. What it would take to build the unit, less wear. Fannie Mae doesn't require it except for manufactured homes, and won't accept an appraisal built only on cost.

Builders add their own rule of thumb. Snap ADU, a San Diego builder, says a new ADU adds about 100 times its monthly rent, so roughly $350,000 for a unit renting at $3,500. That's a seller's estimate, not an appraisal method, but it's a useful check against cost.

On these numbers, the ADU returns somewhere between 80% and 93% of its cost in value, before any rent you collect while you own it. A flat lot with good comps could do better; a steep lot in a neighborhood with few ADU sales could do much worse. Price your own project with the ADU cost calculator or see what an ADU costs in San Diego.

Why ADU value isn't the same as cost

Buyers pay for what they can see and use: a second home, rent, space for family. They don't pay for the money you spent getting there. Three kinds of spending tend to fall through the gap:

• Site work. Snap ADU puts a separate SDG&E meter at $10,500 to $15,000, retaining walls at $20,000 to $30,000 or more, and a sewer pump at about $5,000. A buyer sees the same ADU whether your lot needed them or not.
• Fees and design. Permits, plan checks and school fees are real costs with no resale line of their own.
• Finishes above the neighborhood. The San Diego County Assessor names this an “over improvement for the area,” where construction cost exceeds the market value added. Appraisers see it the same way.

What drives ADU value

Two ADUs that cost the same can appraise very differently. These are the factors appraisers and lenders write about.

The classification row matters more than it looks. Fannie Mae has the appraiser decide whether a property is one unit with an ADU or a two- to four-unit property, based on things like separate utility meters, a unique postal address and whether the unit can be legally rented. As a two-unit property, the income approach becomes required and different loan rules apply. Neither is better; just know which one a buyer's lender will see. The condo route is covered in selling an ADU separately.

How lenders count an ADU

Lenders care about two numbers: the appraised value, which caps what they'll lend, and the ADU's rent, which can help you qualify. The major programs now count ADU rent, with limits.

Value matters most when you borrow to build. For a Fannie Mae HomeStyle renovation loan, the lender sizes the loan on the “as completed” appraised value: on a purchase, the lesser of that value or the price plus renovation costs, and on a refinance, renovation costs can't exceed 75% of it. If the appraiser gives your planned ADU less value than it costs, you can borrow less. Compare loan types in the ADU financing guide and run payments in the ADU loan calculator.

ADU value when you sell

A permitted ADU widens your pool of buyers: families with a parent to house, buyers who want rent to help with the mortgage, and investors. A few things change hands with it.

• The buyer's property tax resets. A sale is a change in ownership, so the whole property is reassessed to market value, ADU included. Buyers who run the numbers will price that in. Our ADU property tax guide explains how the assessor treats the unit while you own it.
• Your capital gains exclusion may not cover the ADU. IRS Publication 523 says you generally can't exclude gain on a separate part of your property used to produce rental income, and gives a duplex with one unit rented as an example. Depreciation you claimed on a rental can't be excluded either. Ask a tax preparer before you list.
• A lease can help the buyer qualify. If a lease transfers to the buyer, their lender needs the signed lease to count the ADU rent on the purchase.

Disclosure, unpermitted units and the listing details buyers check are covered in our guide to ADUs in real estate.

Protecting the value you build

• Close the permit. In the City of San Diego, the final inspection is your approval to occupy. A permit history is the first thing a buyer's agent and appraiser look for. See how ADU permits work in San Diego.
• Design for your market. Fannie Mae wants an appraisal to show the improvements are acceptable for the market. Match the size, bedroom count and finishes to what nearby renters and buyers expect.
• Keep every record. Plans, permits, invoices, warranties and the certificate of final inspection help an appraiser and reassure a buyer.
• Hire a licensed builder. Shoddy or unfinished work drags value down fast. Read how to hire an ADU contractor, check a contractor's license, or start with our verified ADU builders in San Diego.

Common questions