ADUs and what they do to your property

On the rules themselves: state ADU law has changed repeatedly, and the relevant Government Code sections were renumbered in 2024. What is permitted on your specific parcel depends on current state law and your local ordinance. Start with California HCD and your city or county planning department. We are brokers - we will not guess at code, and you should be wary of an agent who does.

What follows is the part we can speak to: what an ADU does to value, appraisal, lending and a future sale.

Permitted and unpermitted are different assets

This is the single most consequential distinction, and the two are often physically indistinguishable on a walkthrough.

• A permitted ADU appears in the property record, can be described as a dwelling unit in a listing, is generally counted by an appraiser, and its rent can often be considered by a lender.
• An unpermitted conversion — a garage turned into a studio, a bootlegged back unit — cannot properly be advertised as a legal unit, is treated cautiously or ignored entirely by appraisers, and can create real problems in escrow.

Owners frequently believe the second one is worth what the first one is. It is generally not, and the gap widens the moment a buyer needs financing.

The disclosure problem when you sell

Unpermitted work is a disclosure matter. Hoping a buyer does not notice is not a strategy — appraisers, inspectors and neighbors all notice, and a concealed unpermitted unit discovered mid-escrow is how transactions collapse and how sellers end up in disputes after closing.

Handled openly it is usually manageable. Buyers discount for it, price it in, and proceed. The damage comes from concealment, not from the condition itself. Tell us early and we will tell you how it is likely to be received.

Appraisal is the part people do not anticipate

An ADU does not automatically add its construction cost to appraised value. Appraisers work from comparable sales, and in areas where few comparable properties have ADUs there may be limited data to support a large adjustment. It is entirely possible to spend substantially on a unit and see a smaller change in appraised value — particularly early in a market's adoption.

That is not an argument against building one. It is an argument against assuming the money returns as value on paper. The return is often better measured in rent than in appraisal.

Financing, both directions

Financing construction, and financing the purchase of a property that already has one, are separate questions and both have moved in recent years — including how much prospective ADU rental income a lender will count toward qualifying.

Because Juliet is a licensed mortgage broker as well as a real estate broker (NMLS ID 316166), this is a question we can answer inside the firm against current lender guidelines rather than sending you off to find out. Ask before you build, not after.

What it means for a future sale

• Your buyer pool shifts. A property with a legal second unit appeals to buyers wanting rental income or multigenerational space, and less to those wanting a straightforward single-family home.
• Keep the paperwork. Permits, final sign-off and plans are what let a listing describe the unit accurately and let an appraiser credit it. Lost paperwork costs real money at sale.
• Improvements affect your tax basis. A permitted ADU is generally a capital improvement, which raises basis and can reduce taxable gain later. Keep the receipts. More on that →
• Expect a partial reassessment. New construction typically triggers reassessment of the added value — the existing home's base is not usually disturbed, but the new unit is assessed. Confirm with your county assessor.

What an HOA can and cannot do about it

This is widely misunderstood, including by agents. On a lot zoned for single-family residential use, California law makes void and unenforceable any governing-document provision that effectively prohibits or unreasonably restricts the construction or use of an ADU or junior ADU. "Use" includes renting it.

So an HOA in a single-family planned development generally cannot simply ban you from renting a compliant ADU. What it can still do is impose reasonable restrictions, and it can bar short-term rentals of under 30 days.

The limit worth knowing: this protection is written for lots zoned single-family. Condominiums and multifamily-zoned property are a different question and should not be assumed to carry the same protection. If that is your situation, get it checked rather than relying on the general rule.

Unpermitted units now have a legalization path

Worth knowing before you assume an unpermitted conversion is simply a liability. California has created a route to legalize unpermitted ADUs built before 2020, under which a local agency generally cannot require correction of nonconforming zoning or building standards unless there is an actual health-and-safety problem, and impact and utility-connection fees are largely barred.

That materially changes the calculation on an older unpermitted unit - from "discount it and disclose" to "find out whether it can be legalized first". Ask your local planning department, and get the specifics confirmed for your property before making a decision either way.

If you rent it out, the tax picture changes

An ADU you rent creates exactly the complications that make a later sale more expensive: depreciation on the rented portion cannot be excluded when you sell, and part of the property stops being purely your principal residence. How that works → Worth understanding before you build, not when you sell.

If you are buying a property that has one

Ask for the permit and the final inspection sign-off, not just an assurance that it was done properly. Confirm whether the unit is reflected in the assessor's record. And have your inspector look at it as carefully as the main house — converted spaces frequently have the electrical, drainage and ventilation shortcuts you would expect.