Short answer: If you want the best ADU rules and the highest ADU rents, Costa Mesa wins: 1,200 sq ft, two stories, no parking required and up to three ADUs on one lot. If you want the lowest coastal entry price and the most buyer leverage right now, Huntington Beach wins. If you want top schools, a newer house and a long-term hold, Irvine wins, but it’s the most expensive, the thinnest ADU market, and the hardest to make pencil. None of the three cash flows at 25% down after you build. At 50% down, Huntington Beach and Costa Mesa roughly break even and Irvine still runs short.
This is the coastal and South County version of my best cities to buy a home and add an ADU list. These three cities border each other, and buyers who can spend $1.5M to $2M usually narrow it down to them. Below is how they compare on price, ADU rules, rents, market speed and the monthly payment math.
Last updated: October 2026. Dylan Serna, The ADU Realtor.
Huntington Beach vs. Costa Mesa vs. Irvine at a Glance
| Huntington Beach | Costa Mesa | Irvine | |
|---|---|---|---|
| Median sale price, all homes (Redfin, Aug–Sep 2026) | About $1,377,000 | About $1,549,000 | About $1,449,000 (mostly condos and townhomes) |
| Median asking price, homes with an ADU (my Oct. 2026 reports) | About $2,425,000 (6 active) | About $2,200,000 (7 active) | Too few listings to report |
| Max detached ADU size | 1,200 sq ft | 1,200 sq ft | 800 to 1,200 sq ft (state rules) |
| Detached ADU height | 16 ft (more in some cases) | 27 ft or 2 stories | 16 ft (18 ft with a 2-story house or near transit) |
| ADUs on a single-family lot (2026) | 1 ADU + 1 JADU | 1 detached + 1 conversion ADU + 1 JADU | 1 ADU + 1 JADU |
| ADU parking | Waived within ½ mile of transit | Optional | Up to 1 space, with state exemptions |
| ADUs finaled 2005–2025 | 354 (89 in 2025) | 206 (70 in 2025) | 59 (25 in 2025) |
| ADU rents on listings | $2,500 to $5,000 | $3,500 to $5,750 | Limited data |
| Rule that trips up buyers | Coastal Zone permit | Objective design standards on 2-story ADUs | HOAs, small lots and Mello-Roos |
Sources: Costa Mesa Municipal Code § 13-35, the Huntington Beach ADU page, Irvine Zoning Ordinance Chapter 3-26, Redfin city data, CRMLS, and ADU counts from Cal State Fullerton’s ADU report. Confirm any parcel with the city before you write an offer.
What It Costs to Get In
- Huntington Beach has the lowest citywide median of the three at about $1.38M, up 4.6% year over year. The ADU-friendly stock is 1960s and 1970s single-story tracts on 6,000 to 7,500 sq ft lots, mostly north of Adams and inland of Beach Blvd.
- Costa Mesa runs about $1.55M. Detached houses with room for an ADU usually start around $1.6M on the Westside and run well past $2M on the Eastside. The cheapest ADU home for sale this month was $1.6M, and it’s a receivership fixer.
- Irvine shows a median of about $1.45M, down 6.5% year over year, but that number is pulled down by condos and townhomes. A detached house with a real backyard in an older village like University Park, Turtle Rock or Northwood typically costs $1.9M or more.
For the payment math below, I use $1.55M for Huntington Beach, $1.7M for Costa Mesa and $1.95M for Irvine as realistic prices for a 3-bedroom house on a lot that fits a 2-bedroom ADU.
ADU Rules Compared
All three follow state ADU law, so the basics match: 4-foot side and rear setbacks, ministerial approval within 60 days, no owner-occupancy for an ADU by itself, no impact fees under 750 sq ft, and no short-term rentals. State rules are on California HCD’s ADU page. Here’s where they differ.
Costa Mesa: the most flexible ADU code in coastal OC
Costa Mesa allows a detached ADU up to 1,200 sq ft and up to two stories and 27 feet, plus a conversion ADU and a JADU on the same single-family lot. Parking is optional. That combination is rare. A two-story ADU lets you build a 2-bed, 2-bath unit on a smaller footprint and keep the backyard.
The catch is design. Second stories must sit 25 feet back from the front property line, side windows within 25 feet of a neighbor need high sills, and roof decks aren’t allowed. Neighborhood matters a lot here too. I break down the Eastside and why Halecrest wins on value in separate posts.
Huntington Beach: good rules, one big coastal caveat
Huntington Beach allows a detached ADU up to 1,200 sq ft at 16 feet, plus a JADU. The city also offers a free pre-approved 490 sq ft ADU plan that can save months of design time. Two things to know:
- The Coastal Zone. Roughly a third of the city is in it. A lot there may need a Coastal Development Permit on top of the building permit. Check before you pay for drawings. Details are in my Huntington Beach ADU guide.
- The city’s fight with the state. HB has lost its housing law case at every level, including the U.S. Supreme Court. That fight has mostly confirmed that state ADU law applies in HB. I explain what it means in Huntington Beach’s housing law fight and ADU buyers.
HB also has the most ADU history of the three: 354 finaled since 2005 and 89 in 2025 alone. More finished ADUs means better comps when you appraise or sell.
Irvine: the rules got better, the lots didn’t
Irvine’s old ADU ordinance required owner-occupancy, a 5,000 sq ft minimum lot and a 15.5-foot height cap. The state found it out of compliance, and Irvine re-adopted its ADU chapter in September 2025 to follow state law. Today you get 1 ADU plus 1 JADU, 16 feet (18 feet next to a 2-story house) and an 800 sq ft unit the city can’t zone out.
The real limits in Irvine are physical and financial:
- Small lots. Newer villages are often built on 3,500 to 5,000 sq ft lots with little backyard. Older villages have the lots that work.
- HOAs. Almost every Irvine home is in one. Under California Civil Code § 4751, an HOA can’t ban an ADU or unreasonably restrict one, but it can add architectural review. Budget time for it.
- Mello-Roos. Many newer Irvine neighborhoods carry a special tax on top of the base property tax. Check the tax bill, not just the price.
Irvine finaled only 59 ADUs from 2005 to 2025, fewer than Costa Mesa builds in a single year. That means thin appraisal comps.
What changes in 2027
Starting January 1, 2027, AB 956 allows two detached new-construction ADUs on a single-family lot, and SB 1117 limits impact fees to the space above 750 sq ft. That helps Huntington Beach and Irvine catch up to Costa Mesa on unit count, if the lot is big enough. My breakdown is in what AB 956 and SB 1117 mean for ADU owners.
What ADUs Rent For
| ADU type | Huntington Beach | Costa Mesa | Irvine (estimate) |
|---|---|---|---|
| Studio or JADU | $2,000 to $2,500 | $2,100 to $2,600 | $2,200 to $2,600 |
| 1 bed / 1 bath | $2,500 to $3,100 | $2,700 to $3,300 | $2,800 to $3,300 |
| 2 bed / 2 bath | $3,200 to $3,800 | $3,500 to $4,500 | $3,300 to $4,000 |
| Large new 1,100 to 1,200 sq ft unit | $4,750 to $5,000 | $5,000 to $5,750 | Not enough data |
Huntington Beach and Costa Mesa ranges come from rented ADUs on listings in my October Huntington Beach report and October Costa Mesa report, including a new 1,187 sq ft Costa Mesa ADU leased at $5,750. Irvine has too few rented ADUs on the MLS to report, so those numbers are my estimates based on Irvine apartment rents.
Costa Mesa has the strongest ADU rents of any city I track, driven by South Coast Plaza, John Wayne Airport jobs and the beach. Irvine’s rents are high too, but ADUs compete with a huge supply of new apartments.
How Fast ADU Homes Are Selling
- Huntington Beach: 6 active, 5 of 6 have cut price, and both September sales closed about $200,000 under asking with seller credits. This is the most buyer-friendly market of the three.
- Costa Mesa: 7 active, median 35 days, 4 of 7 cut price. But a home with a rented 1,187 sq ft ADU sold in 5 days for $150,000 over asking, all cash. Good ADUs still get bid up.
- Irvine: Homes overall take about 61 days to sell, the slowest of the three, and prices are down year over year. Very few listings have a permitted ADU.
The Payment Math: Buy a House, Build a 2-Bedroom ADU
Same method as all my posts: total monthly payment (principal, interest, taxes and insurance) against total rent. The scenario is identical in each city. Buy a 3-bedroom house and pay cash for a 2-bedroom detached ADU at about $350,000 all-in, then rent both.
Assumptions: 7.75% investment rate on a 30-year loan, property tax at 1.15% of purchase price plus build cost (no Mello-Roos), and $250 a month for insurance. Main-house rents are my estimates for a 3-bedroom in each city. ADU rents are mid-range from the table above.
| Huntington Beach | Costa Mesa | Irvine | |
|---|---|---|---|
| Purchase price | $1,550,000 | $1,700,000 | $1,950,000 |
| Main house rent + ADU rent | $5,000 + $3,400 = $8,400 | $5,200 + $3,800 = $9,000 | $5,500 + $3,600 = $9,100 |
| 25% down: cash in (down + build) | $737,500 | $775,000 | $837,500 |
| Monthly PITI | About $10,400 | About $11,350 | About $12,930 |
| Rent minus PITI | About -$2,000 | About -$2,350 | About -$3,830 |
| 50% down: cash in (down + build) | $1,125,000 | $1,200,000 | $1,325,000 |
| Monthly PITI | About $7,620 | About $8,300 | About $9,440 |
| Rent minus PITI | About +$780 | About +$700 | About -$340 |
How I read this table:
- These are appreciation plays. At 25% down, all three run $2,000 to $3,800 a month short. You’re buying land near the coast or in a top school district and letting the ADU carry part of the cost.
- At 50% down, Huntington Beach and Costa Mesa turn slightly positive. Irvine still doesn’t cover its payment, and Mello-Roos would widen that gap.
- Costa Mesa can beat this table. Add a conversion ADU or JADU, which Costa Mesa allows alongside the detached unit, and a third rent can close most of the 25%-down gap.
- Living in the main house changes everything. If you live in the front and rent the ADU, your out-of-pocket cost drops by the ADU rent, and you can buy with far less than 25% down.
These are planning numbers, not quotes. Rate, insurance, HOA dues, any Mello-Roos and your build bid will change them. I re-run this for every property a client is serious about.
Which City Fits Your Plan?
Choose Huntington Beach if…
- You want a beach city at the lowest entry price of the three.
- You want to negotiate hard. Sellers are cutting price and paying buyer credits right now.
- You’re buying inland of the Coastal Zone, or you’re willing to run the coastal permit.
Choose Costa Mesa if…
- You want the highest ADU rent and the most units on one lot.
- You want the option of a two-story ADU with no required parking.
- You can move fast when a well-priced home with ADU room hits the market.
Choose Irvine if…
- Schools and a newer home matter more to you than monthly cash flow.
- You’ll live in the main house and use the ADU for family or partial rent.
- You can find an older-village lot with real backyard space and a cooperative HOA.
Whichever city you pick, verify permits, the Coastal Zone, HOA rules and the tax bill during your inspection period with my escrow ADU verification checklist.
Frequently Asked Questions
Which is cheaper for an ADU investment: Huntington Beach, Costa Mesa or Irvine?
Huntington Beach. Its median sale price is about $1.38M, compared with about $1.55M in Costa Mesa. Irvine’s median is about $1.45M, but detached houses with room for an ADU there usually cost $1.9M or more.
Can I build a two-story ADU in Costa Mesa, Huntington Beach or Irvine?
Costa Mesa allows detached ADUs up to two stories and 27 feet. Huntington Beach and Irvine generally cap detached ADUs at 16 feet, with some exceptions for taller main houses or transit areas.
Can my HOA in Irvine stop me from building an ADU?
No. California Civil Code § 4751 makes HOA rules that prohibit or unreasonably restrict ADUs void. The HOA can still require architectural review and reasonable design standards.
Do I need a coastal permit for an ADU in Huntington Beach?
Only if the property is in the Coastal Zone, which covers roughly a third of the city near PCH, the beach and the wetlands. Check the city’s zoning map before you buy.
Where do ADUs rent for the most?
Costa Mesa. ADUs on current listings and recent sales rent for $3,500 to $5,750 a month, compared with $2,500 to $5,000 in Huntington Beach.
Can I rent an ADU on Airbnb in these cities?
No. All three require long-term rentals for ADUs: 31 days minimum in Costa Mesa and for newer ADUs in Huntington Beach, and at least 30 days under state law everywhere.
Compare Real Properties, Not Averages
Tell me your budget and whether you’ll live there or rent both units. I’ll pull homes in Huntington Beach, Costa Mesa and Irvine that fit a permitted ADU, with projected rents, build cost, HOA and tax details for each one.
👉 Book a buyer ADU consult call to go through your options with Dylan
Prefer to talk now? Call Dylan Serna, ADU Realtor at 714-860-2868.
Dylan Serna | The ADU Realtor | eXp Realty | DRE #02217359
This post is general information, not legal, tax or financial advice. Prices, rents and payments are estimates based on October 2026 MLS data and public sources. Confirm ADU rules, HOA rules and coastal requirements for any specific property.
