Accessory dwelling units — ADUs — have become one of the most talked-about topics in Hermosa Beach real estate over the past few years, and for good reason. California law has made it significantly easier to add a second unit to your property, and Hermosa Beach has followed suit. If you own a home here and you’re wondering whether an ADU makes sense, here’s what the city actually requires, what it realistically costs, and when it pencils out financially.
What Is an ADU?
An ADU is a secondary dwelling unit on a single-family or multi-family residential lot. In Hermosa Beach, this can take a few different forms:
- Detached ADU — a separate structure in your backyard (the classic “granny flat”)
- Attached ADU — an addition to your existing home with its own entrance
- Garage conversion — converting an existing attached or detached garage into living space
- Junior ADU (JADU) — a smaller unit (max 500 sq ft) carved from existing interior space, typically with a kitchenette
Each type has different size limits, setback requirements, and permit implications — which is why it matters to understand the specifics before you hire a designer or contractor. Our Hermosa Beach homeowner resources page has links to all the related guides.
Hermosa Beach ADU Rules (Key Points)
California state law (AB 68 and subsequent legislation) sets a baseline that cities must comply with, but cities can add their own local standards on top. Here’s what matters most in Hermosa Beach:
Size Limits
- Detached ADU: up to 850 sq ft (studio or one-bedroom) or 1,000 sq ft (two-bedroom) — Hermosa Beach’s local code is stricter than the state baseline of 1,200 sq ft (HB Municipal Code Ch. 17.21)
- Junior ADU: maximum 500 sq ft, must be within existing structure
- Garage conversions: typically match the existing footprint
Setbacks
- State law requires cities to allow at least 4-foot side and rear setbacks for detached ADUs
- Hermosa Beach applies local setback rules in some zones — the Planning Division (310-318-0242) can tell you your specific parcel’s requirements before you design anything
Height
- Detached ADUs: limited to 16 feet for a one-story structure on a single-family lot (confirmed per HB Municipal Code Ch. 17.21)
- If you’re building above a garage, height exceptions may apply — this is where the Height Limit Exception permit ($5,082) may come into play
Owner Occupancy
- California permanently eliminated owner-occupancy requirements via AB 976, effective January 1, 2024 — you do not have to live on the property to build or rent an ADU. This is permanent law with no sunset date (Gov. Code § 66315)
Parking
- If you convert a garage, you generally do not have to replace the parking — state law protects this
- ADUs within half a mile of public transit also typically don’t require additional parking
What Permits Does an ADU Require in Hermosa Beach?
Yes — you need permits. An ADU is a new dwelling unit and requires building, plumbing, mechanical, and electrical permits through the city’s Building and Safety Division. Our Hermosa Beach permit guide covers the full permit process in detail.
Hermosa Beach offers a Concurrent Development Review Process — meaning Planning, Building, and Public Works review your plans simultaneously rather than in sequence. This can meaningfully speed up your approval timeline.
The plan submittal process typically requires:
- Site plan, floor plan, roof plan, and elevations
- Structural plans and calculations (if structural changes are involved)
- Energy code compliance documentation (California Title 24)
- CAL Green Code compliance
- Geotechnical/soil report if new footings are being poured
- LA County Fire approval if building within 5 feet of a property line
- Water Efficient Landscape Ordinance (WELO) determination
You can also request a Preliminary Planning Review (approximately $200) before submitting full plans — this is worth doing if you’re still in the design phase and want to confirm feasibility before spending money on architecture drawings.
Contact: Hermosa Beach Community Development — Building and Safety: 310-318-0235, Monday–Thursday 7am–6pm. Email: CommunityDevelopment@hermosabeach.gov
What Does an ADU Cost to Build in Hermosa Beach?
Construction costs in coastal LA are high — there’s no way around it. For a detached ADU in Hermosa Beach, here’s a realistic range:
| ADU Type | Estimated Construction Cost | Notes |
|---|---|---|
| Garage conversion (JADU) | $80,000–$150,000 | Lower cost — using existing structure |
| Attached ADU addition | $150,000–$300,000+ | Depends on size and finish level |
| Detached ADU (new construction) | $250,000–$500,000+ | Full build; higher in HB due to lot constraints and coastal premium |
Permit fees are calculated based on project valuation. For a project valued at $100,000–$200,000, you’re looking at building permit fees of roughly $1,600–$2,500 plus plan check (80% of permit fee), plus plumbing, mechanical, and electrical permits on top of that. Budget approximately $5,000–$10,000+ in permit fees for a full detached ADU build. Our complete Hermosa Beach permit fee breakdown has the exact numbers by project type.
Note: Illegal construction in Hermosa Beach is subject to quadruple permit fees — so skipping the permit process is not a financially sound shortcut.
The Density Bonus Program
If your property is a multi-family parcel or if you’re developing at higher density, Hermosa Beach participates in California’s Density Bonus Program, which can allow additional units beyond what base zoning permits in exchange for including affordable units. This is more relevant for developers than typical single-family homeowners, but worth knowing if you’re evaluating a larger project.
Does an ADU Make Financial Sense in Hermosa Beach?
Here’s the honest answer: it depends on your specific lot, your goals, and your timeline.
Hermosa Beach rents are strong. A well-designed 600–800 sq ft ADU in a desirable part of Hermosa can realistically command $2,800–$4,000/month in long-term rent — or more as a short-term rental (with a separate STVR permit). At those rental rates, a $250,000 garage conversion could generate a 13–18% annual cash return before expenses, which is compelling in any market.
The variables that can make or break the math:
- Lot size and existing coverage — many Hermosa lots are constrained, though properties in the Valley and Hills sections tend to have the largest lots and most ADU potential. A preliminary planning review will tell you quickly what’s buildable.
- Design quality — a thoughtfully designed ADU adds more resale value than a generic conversion
- Short-term vs. long-term rental — STVR permits in Hermosa require a separate application ($2,173 initial) and come with usage restrictions
- Your timeline — permitting and construction typically takes 12–24 months from start to first rent check
If you’re considering an ADU as part of a home purchase decision, I’m happy to walk through the numbers for a specific property. It’s one of the more interesting value-add conversations in this market right now.
How to Get Started
- Request a Preliminary Planning Review from Hermosa Beach Community Development ($200) — this tells you what’s buildable on your specific parcel before you invest in design
- Hire a local architect who has done ADU projects in coastal LA — the permitting nuances matter
- Get contractor bids after design is complete, not before — cost estimates without plans are not reliable
- Submit for building permit — use the Concurrent Development Review Process to speed up the timeline
Questions? Let’s Talk
Important: City regulations and fee schedules change. Before starting an ADU project, verify current requirements directly with Hermosa Beach Community Development at 310-318-0235. This guide is informational — the city has final say on what’s allowed for your specific property.
ADU feasibility is one of the things I find myself discussing more and more with buyers who are evaluating Hermosa Beach properties. If you’re thinking about adding a unit, buying a property that already has one, or just want to understand the options, feel free to reach out.
Cecilia Agraz | Bayside Real Estate Partners / Stroyke Properties Group
310-803-9338 | cecilia@manhattanhermosahomes.com
Cecilia Agraz
South Bay neighbor and Realtor® focused on clear guidance and low‑stress moves in Manhattan Beach & Hermosa Beach.