Short answer: Filter for single-family homes on lots of 6,000+ square feet with a small house (living area under about 25% of the lot). Then search listing remarks for access keywords like “RV access,” “detached garage,” “corner lot,” and “alley.” Screen every hit on satellite view and the county parcel map before you tour. Finally, watch expired, withdrawn, and price-cut listings, because that’s where the best ADU lots sit the longest.
Every week someone sends me a listing that says “ADU potential” in the headline. Most of the time, the lot is 4,800 square feet, the house already covers half of it, and there’s a pool right where the ADU would go.
The opposite also happens. The best ADU lot I’ll see all month is listed as “charming starter home, great backyard,” and never says the word ADU once.
That’s the problem. There is no filter on Zillow, Redfin, or the MLS that finds homes that can fit an ADU. You have to build the search yourself. Here’s how I do it.
Step 1: Set Your Buy Box Before You Search
If you start scrolling without numbers, every big backyard looks like a deal. Decide these four things first:
| Buy box item | What I recommend for a detached ADU play |
|---|---|
| Lot size | 6,000 sq ft minimum, 7,000+ preferred |
| House size | Under ~1,600 sq ft (small house, big lot) |
| Total budget | Purchase price + $250K to $400K for the build |
| Target cities | 2 to 4 cities with strong rents and deep sales data |
The budget line is the one buyers underestimate. The house is only part of the cost. I walk through every dollar, from down payment to first rent check, in what it really costs to buy a home and add an ADU in Orange County.
A quick note on lot size: 6,000 square feet is my practical floor, not a legal one. State law says a city can’t use lot size, lot coverage, or floor area rules to block an ADU of at least 800 square feet with 4-foot side and rear setbacks. So smaller lots can legally get an ADU. They just usually get a cramped one that rents for less.
Step 2: Build the Search Filters (Zillow, Redfin, or MLS)
Here are the exact filters I set up for investors.
Core filters:
- Property type: Single-family detached
- Lot size: 6,000 sq ft minimum
- Home size: Max 1,600 sq ft (this forces “small house, big lot”)
- Year built: Optional, but 1940s to 1960s tracts in OC and LA tend to have the deepest, most regular lots
The house-to-lot ratio trick: Divide the home’s living area by the lot size. If it’s under 20% to 25%, there’s usually room for a detached ADU with yard left over for both units. A 1,100 sq ft house on a 6,500 sq ft lot is 17%. That’s what you want.
Keyword searches: Most portals and the MLS let you search listing remarks. These are the words that actually signal ADU room:
| Keyword | Why it matters |
|---|---|
| “RV access” or “RV parking” | A 10 to 12 foot side yard for construction and a tenant entrance |
| “Detached garage” | Usually means a side driveway, plus a garage you might convert |
| “Corner lot” | Second street frontage for a separate entrance |
| “Alley” or “alley access” | Rear access without touching the side yard |
| “Long driveway” or “gated driveway” | Same as above, often missed |
| “Oversized lot” or “deep lot” | Depth matters more than total square footage |
| “Bonus room” or “converted garage” | Possible JADU or existing unit to legalize |
| “SB9” or “lot split” | Seller already looked into density |
Skip “ADU potential” as your main keyword. Agents use it on almost everything, and it filters in more bad lots than good ones.
A real example from Lakewood: a 1947 home on Hayter that closed in September 2026 for $1,030,000 mentioned a “long gated driveway… possible boat or RV parking” deep in the description. That’s exactly the language that tells you the backyard is reachable. It never appeared in the headline.
For more on why lot depth, corner position, and garage placement matter, see my earlier guide on how to search for homes with ADU potential without wasting time on the wrong lots.
Step 3: Run a 10-Minute Desk Screen Before Every Tour
Filters get you a list. This screen tells you which ones are worth driving to. I run every property through these six checks from my laptop.
1. Satellite view (2 minutes). Look at the backyard. Is there a pool, a big tree, or a slab of hardscape where the ADU would go? Is there a side driveway or gate? If both side yards are narrow with a fence, access will cost you.
2. County parcel map (2 minutes). Confirm lot size and shape. In Orange County, use the OC Assessor’s property information and parcel maps. In LA County, use the LA County Assessor portal. A 6,000 sq ft lot that’s 50′ x 120′ works very differently from one that’s 75′ x 80′.
3. Zoning (1 minute). For properties in the City of Los Angeles, ZIMAS shows zoning, hillside status, and overlays in one place. For OC cities, check the city’s zoning map. You want single-family residential zoning, or multifamily if you’re looking at a multi-unit lot.
4. Fire hazard zone (1 minute). Check the state fire hazard severity zone map. Very High zones can add fire-rated construction, insurance cost, and in some cities, extra ADU restrictions.
5. Flood zone (1 minute). Pull the address on FEMA’s Flood Map Service Center. Parts of Seal Beach, Huntington Beach, and Long Beach sit in flood zones that change foundation requirements and insurance.
6. Coastal zone (1 minute). If the property is near the coast, check whether it falls inside the California Coastal Zone boundary. Coastal zone lots can require a coastal development permit, which adds review time.
If a property passes all six, it’s worth a tour. If it fails one, find out how much that failure costs before you write off the property. A flood zone is a cost. A pool in the only buildable spot is often a dealbreaker, though not always. Here’s what to do when an ADU-potential property has a pool.
Step 4: Study What Already Sold With a New ADU
The fastest way to learn what lots work in a city is to look at homes where someone already did it.
Search closed sales from the last 12 months with “ADU” in the remarks and a year-built on the ADU of 2023 or later. Then pull up the satellite view and compare the before and after. You’ll quickly see which lot sizes, shapes, and layouts the city approves.
Here’s one from Lakewood that shows the model clearly:
| 5867 Adenmoor Ave, Lakewood | |
|---|---|
| Lot size | 6,019 sq ft |
| Main house | 864 sq ft, built 1941 |
| House-to-lot ratio (before ADU) | ~14% |
| ADU added | 669 sq ft, 2 bed / 2 bath, detached, completed 2025 |
| List price | $999,000 |
| Closed price | $1,070,000 (September 2026) |
| Days on market | 15 |
That’s the textbook small-house, big-lot property. A 14% ratio left plenty of room for a detached 2/2 with its own address, and the finished property sold over asking in two weeks. If you find a lot that looks like the “before” version of this, you’ve found your target. Lakewood is full of them, which is why I call it the city with the most ADU potential in LA County.
Closed sales also give you rent data. Once you know what size ADU fits, check what comparable ADUs rent for in that city to see if the numbers work.
Step 5: Look Where Other Buyers Aren’t Looking
The best ADU lots often aren’t the new listings. They’re the ones other buyers already scrolled past.
Expired and withdrawn listings. A seller whose home didn’t sell is often more flexible on price and terms. Ask your agent to pull expireds in your target cities with lots over 6,000 sq ft.
Listings with 45+ days on market and price cuts. Right now, this is a big pool. In my October 2026 updates, homes in Anaheim are sitting two-plus months, and price cuts are showing up across most OC cities. With rates above 7%, buyers have real leverage on ADU properties this fall.
Probate and trust sales. Older owners who bought in the 1960s and 1970s often have exactly the kind of small, original house on a big lot that investors want. These sales tend to be priced for condition, and the condition doesn’t matter much when your plan is the backyard.
Homes with dated or “needs TLC” descriptions. Owner-occupant buyers skip these. Investors who care about the lot shouldn’t.
RV access lots. These are a niche of their own. The wide gated side yard does double duty as construction access and a private tenant entrance.
Step 6: Set Alerts, Move Fast, Then Verify in Escrow
Once your filters and keywords are dialed in, save the search and turn on instant alerts. Good ADU lots priced right still move quickly. The Adenmoor property above went under contract in about two weeks.
When you find one, don’t rely on the listing’s description. Use your contingency period to confirm what you can build. That means calling the city’s planning counter, pulling the permit history, checking for easements on the preliminary title report, and getting a rough site plan if the numbers are tight. I lay out the full process in how to verify ADU potential while you’re in escrow.
Pay close attention to unpermitted additions on the main house. They can hold up your ADU permit until they’re resolved. Here’s the unpermitted addition problem nobody warns you about.
Red Flags That Knock a Listing Out
| Red flag | Why it matters |
|---|---|
| Pool in the backyard’s only open area | Removal adds $15K to $40K+ and may still leave too little room |
| Both side yards under 5 ft, no alley | Hard construction access, no separate tenant entrance |
| Utility or drainage easement across the back | You can’t build on it |
| Steep slope or hillside designation | Grading, retaining walls, and engineering costs |
| Unpermitted additions on the main house | Can delay or block your ADU permit |
| Main house covers most of the lot | No room for a detached unit (JADU or conversion only) |
What’s not a red flag: an HOA. Under California law, HOAs can’t prohibit or unreasonably restrict ADUs on single-family lots. They can still apply reasonable design rules, so read the CC&Rs.
For the full statewide rule set, the HCD ADU Handbook is the official reference every city has to follow.
Frequently Asked Questions
Can I search Zillow or Redfin for homes that can fit an ADU?
Not directly. There’s no ADU potential filter. Use a 6,000+ sq ft lot minimum, a maximum home size around 1,600 sq ft, and keyword searches like “RV access,” “detached garage,” “corner lot,” and “alley.” Then screen each result on satellite view.
What size lot do I need to fit an ADU?
Legally, almost any single-family lot can take some type of ADU. For a detached, multi-bedroom ADU that leaves both units a usable yard, 6,000 sq ft is a practical minimum, and 7,000+ gives you more options.
What is a good house-to-lot ratio for adding an ADU?
Under 20% to 25%. For example, a 1,200 sq ft house on a 6,000 sq ft lot is 20%, which usually leaves room for a detached ADU.
Are listings that say “ADU potential” reliable?
No. Many listings use the phrase loosely. Verify lot size, access, easements, utilities, and city rules yourself, ideally during your escrow contingency period.
Where do investors find the best ADU lots?
Often in expired, withdrawn, and price-reduced listings, probate and trust sales, and older homes with dated descriptions. These get less competition from owner-occupant buyers.
Can an HOA stop me from building an ADU?
No. California Civil Code Section 4751 prevents HOAs from prohibiting or unreasonably restricting ADUs on single-family lots, though reasonable design rules can apply.
Want Me to Run the Search for You?
Tell me your budget and target cities, and I’ll set up an ADU lot search with these filters, screen every hit before it reaches you, and flag the expireds and price cuts other buyers are missing. Every property I send has been checked for lot size, access, and red flags first.
Call Dylan Serna, ADU Realtor at 714-860-2868.
