Adding an accessory dwelling unit to a Manhattan Beach property has gotten meaningfully easier — and more specific — in the last few years. The city passed a revised ADU ordinance in April 2025 (effective May 1, 2025), bringing Manhattan Beach’s local rules in line with California’s expanded ADU laws while adding its own standards on top.
If you’re a homeowner thinking about adding a unit, or a buyer evaluating a property with ADU potential, here’s what the current rules actually allow.
What Changed in May 2025
On April 1, 2025, the Manhattan Beach City Council adopted Ordinance No. 25-0004, amending MBMC Chapter 10.74 (Accessory Dwelling Units). The revised regulations took effect May 1, 2025.
The ordinance also creates local ADU rules for the Coastal Zone — but those are pending certification by the California Coastal Commission (CCC). Until the CCC certifies the amendments, ADUs in the Coastal Zone are governed by state law only.
How Many ADUs Can You Add?
- Single-family lot: 1 ADU + 1 Junior ADU (JADU)
- Multi-family property: 2 new detached ADUs + conversion ADUs up to 25% of the existing unit count
ADU Types and Size Limits
| ADU Type | Max Size | Notes |
|---|---|---|
| Junior ADU (JADU) | 220–500 sq ft | Must be within existing structure; includes kitchenette |
| Studio or 1-bedroom ADU | 850 sq ft | Applies to attached and detached |
| 2+ bedroom ADU | 1,200 sq ft | Detached or attached |
| Attached ADU | 850 sq ft | Also cannot exceed 50% of main dwelling size |
Which Section Makes ADU Most Feasible?
Not all of Manhattan Beach is equally suited for ADU construction — and lot size is the primary constraint.
Sand Section: Lots typically run ~2,700 sq ft. The size is tight, and most existing coverage leaves little room for a detached structure. Garage conversions (creating a JADU from existing space) are the most viable option in the Sand Section. A full detached ADU is possible on some lots, but requires careful analysis.
Tree Section: Lots are larger — typically 5,000–7,500 sq ft — giving more room to work with. Detached ADUs in the backyard are more feasible here, and garage conversions are also common.
Hill Section: Lot sizes are more varied (sometimes significantly larger), and the topography introduces complexity. Detached ADUs are possible on many parcels, but hillside conditions affect construction cost and require careful evaluation.
East Manhattan Beach (Mira Costa, Liberty Village, The Village): Lots in this section are often among the largest in Manhattan Beach — 7,500+ sq ft is not unusual in Mira Costa. ADU construction here has some of the best feasibility in the city, particularly for full detached builds.
Coastal Zone Note
If your property is in the Coastal Zone (primarily the Sand Section, west of approximately Highland Avenue), the city’s new local ADU standards are still pending California Coastal Commission certification. Until that approval comes through, only state ADU law applies to Coastal Zone parcels — which is actually permissive. Contact the Planning Division to confirm what applies to your specific address.
Permit Process
An ADU requires building permits regardless of type. The process involves submitting plans through the Community Development Department for Planning and Building review.
Key items typically required for plan submittal:
- Site plan, floor plan, elevations
- Structural plans and calculations (for new construction)
- California Title 24 energy compliance documentation
- CAL Green compliance
- Geotechnical report if new footings are involved
Contact: Manhattan Beach Planning Division — (310) 802-5520 | planning@manhattanbeach.gov
Hours: Monday–Thursday, 8am–5pm; Friday, 8am–4pm
What Does an ADU Cost to Build in Manhattan Beach?
Construction costs in Manhattan Beach are consistent with coastal LA generally — high. Realistic ranges:
| ADU Type | Estimated Cost | Notes |
|---|---|---|
| JADU / garage conversion | $80,000–$150,000 | Lower cost — using existing structure |
| Attached ADU | $150,000–$300,000+ | Depends on size and finish |
| Detached ADU (new build) | $250,000–$500,000+ | Full new construction; higher in coastal areas |
Permit fees are based on project valuation. For a full detached ADU build, budget $5,000–$10,000+ in permit fees on top of construction costs. For the exact fee schedule, contact the Permit Center at (310) 802-5533.
Does an ADU Make Financial Sense in Manhattan Beach?
The math depends on section, project type, and your goals.
Manhattan Beach long-term rental rates are strong. A well-designed 700–800 sq ft ADU in the Tree Section or East MB could realistically command $3,000–$4,500/month in rent. At those rates, a $250,000–$300,000 garage conversion or attached ADU can produce a respectable return over time.
In the Sand Section, where lot constraints favor JADUs and garage conversions over full detached builds, the calculus is tighter — but the rental demand is there given proximity to the beach.
A few things that affect the financial case:
- Your existing lot coverage — a preliminary planning consultation tells you quickly what’s buildable
- Design quality — a well-designed ADU adds more resale value than a utilitarian conversion
- Short-term vs. long-term rental — STVRs are only permitted in the Coastal Zone with a business license; see MB STVR rules
- Timeline — permitting and construction typically runs 12–18 months from start to occupancy
Manhattan Beach vs. Hermosa Beach for ADUs
If ADU income is a key part of your investment evaluation, Hermosa Beach offers some advantages. Hermosa has larger lots (especially in the Valley section — Poets Knoll lots run up to 24,000 sq ft), more physical space for detached builds, and a city-wide short-term rental program that creates additional flexibility for how you use the ADU. For a comparison, see the Hermosa Beach ADU guide.
That said, Manhattan Beach ADUs still have strong fundamentals — school district access (MBUSD covers every MB home) creates consistent long-term tenant demand that you don’t find everywhere.
Questions? Let’s Talk
Important: City regulations and fee schedules change. Before starting an ADU project, verify current requirements directly with Manhattan Beach Planning at (310) 802-5520. This guide is informational — the city has final say on what’s allowed for your specific property.
ADU potential is increasingly part of how buyers evaluate properties here — both for the income and the flexibility it adds. If you’re buying in Manhattan Beach and want to understand what questions to ask about a specific property, or need a referral to a local architect or contractor who works with ADU projects, feel free to reach out.
Cecilia Agraz | Stroyke Properties Group
310-803-9338 | cecilia@manhattanhermosahomes.com
DRE #01974999
Also reading: ADU Guide for Hermosa Beach | Short-Term Rentals in Manhattan Beach | Manhattan Beach for Real Estate Investors
Cecilia Agraz
South Bay neighbor and Realtor® focused on clear guidance and low‑stress moves in Manhattan Beach & Hermosa Beach.