ADU Constructionin Hermosa Beach, CA
ADU construction in Hermosa Beach is governed by Municipal Code Chapter 17.21, which reviews every ADU and junior ADU ministerially, with no hearing, and decides a complete application within 60 days. A building permit is also required, and coastal review can apply. We read the code on a mirror, so confirm sizes, heights and setbacks with Planning.
Hermosa Beach is built on small lots. A 2016 Coastal Commission report describes a 2,250 square foot lot on The Strand, and Municipal Code 17.08.040 has its own standards for lots of 2,100 square feet or less. Of the city's 10,385 homes, 4,809 are detached houses, the lot type state ADU law is written around, and another 961 are attached houses. About 29.5 percent were built in 1980 or later, so most of the garages and back yards an ADU would use belong to older buildings.
This page covers which ADU class fits a lot, whether a unit will fit on a small lot, coastal review, garage conversions and parking, the design rules that govern windows and screening, fees, and how the job runs. The City's website returned an access error to our tools, and its ADU and permit pages were not opened, so we read Chapter 17.21 on the GoCodebook mirror and quote it as printed. Confirm every number with Planning before you design. Price ranges and phases are on our ADU construction page.
Hermosa Beach Planning and Building rules that apply to ADU construction
Where adu construction permits come from in Hermosa Beach: City of Hermosa Beach Community Development Department, Building and Safety Division.
- Every ADU and JADU in Hermosa Beach needs both an ADU permit and a building permit, reviewed ministerially without a hearing (17.21.040). The City must tell the applicant within 15 business days whether the application is complete, must approve or deny a complete application within 60 days, and if a Coastal Development Permit is needed a complete CDP application must be part of the ADU application and the CDP must be decided within 60 days. The processing fee is set by council resolution (not opened).
- Class 1 (state-regulated) ADUs under 17.21.050(A) include one converted ADU plus one JADU on a single-family lot (inside existing space, plus up to 150 square feet for access) and one new detached ADU of up to 800 square feet with at least 4 foot side and rear setbacks. A detached ADU may not exceed 16 feet in height (18 feet within half a mile walking distance of a major transit stop or high quality transit corridor, and up to 20 feet to match the roof pitch of the main house); an attached ADU is limited to 25 feet or the zone height limit and two stories (17.21.060).
- Class 2 (locally regulated) ADUs in 17.21.070 may be up to 850 square feet for a studio or one bedroom and 1,000 square feet for two or more bedrooms (an attached ADU is capped at 50 percent of the main house floor area, but no standard may force an ADU below 800 square feet), may not push the lot's floor area ratio above 50 percent, must meet 4 foot side and rear setbacks and, as the code prints it, 25 foot front setbacks, and must be one story unless attached.
- Class 2 ADU parking in 17.21.070(G): one off-street space per ADU or per bedroom, whichever is less, which may be in a setback or tandem, with exceptions within half a mile walking distance of public transit, inside a historic district, when the ADU is part of the main house or an accessory structure, when permits are required for on-street parking but not offered to the ADU occupant, and when a car share stop is within one block; no replacement is required for a garage or parking space that is demolished or converted.
- Design standards for a Class 2 ADU in Hermosa Beach (17.21.070): exterior materials, colors and roof slope must match the main house, windows and doors may not have a direct line of sight to an adjoining residential property, windows less than 30 feet from a non-street lot line must be clerestory with the glass bottom at least 6 feet above the floor or use frosted or obscure glass, evergreen screening is required (one 15-gallon plant per 5 linear feet of ADU wall or one 24-inch box plant per 10 feet, at least 6 feet tall when planted, or a 6 foot solid fence), all drought-tolerant from the City's approved plant list, and an ADU on or within 600 feet of a California Register of Historic Resources property must not be visible from a public right of way.
- ADU fees (17.21.080): no impact fee for a JADU or an ADU under 750 square feet, and for an ADU of 750 square feet or more any impact fee must be proportional to the main house floor area. A converted ADU on a single-family lot needs no new utility connection or capacity charge, while other ADUs need a separate utility connection. ADUs may not be rented for fewer than 30 days or sold separately from the lot except as state law allows, a JADU generally requires owner occupancy, and fire sprinklers are required in an ADU only if the main house needs them (17.21.060).
- The Fire Code amendment 110HB in 15.20.030 charges a fire protection improvement fee of $0.09 per square foot of net floor area for residential construction and $0.115 for nonresidential, paid before a building permit for any new structure or expansion, with floor area counting garages, structural decks and balconies and, for additions, only the net increase. Whether the fee applies to a given ADU was not confirmed and should be asked of the Building Official.
- Two-unit projects in the R-1 zone (17.08.050, under Government Code 65852.21) are approved ministerially by the Community Development Director, only for individual property owners (not companies), on a legally subdivided lot with a Subdivision Map Act certificate of compliance, and not on a historic property, in a delineated earthquake fault zone without compliance, or in a 100 year flood hazard area without FEMA floodplain compliance.
Build an ADU in Hermosa Beach: Class 1 and Class 2 units, the junior ADU and the two-unit option
Chapter 17.21 sorts units into two classes. Class 1 follows state law and covers one converted ADU plus one junior ADU on a single-family lot, using existing space plus up to 150 square feet for access, or one new detached ADU of up to 800 square feet with at least 4 foot side and rear setbacks. Class 2 follows local standards, with up to 850 square feet for a studio or one bedroom and up to 1,000 for two or more bedrooms, a floor area ratio no higher than 50 percent, and one story unless attached.
Heights differ by type. A detached unit tops out at 16 feet, 18 feet within half a mile walking distance of a major transit stop, and up to 20 feet to match the roof pitch of the main house, while an attached unit is limited to 25 feet or the zone limit and two stories. An attached ADU cannot exceed 50 percent of the main house floor area, though no standard can push a unit below 800 square feet.
Section 17.08.050 adds a third path in the R-1 zone, a two-unit project approved by the Community Development Director for individual owners only, on a legally subdivided lot, and not on a historic property or in a flood hazard area without floodplain compliance.
Will an ADU fit on a small Hermosa Beach lot? Setbacks, the 25 foot front setback and floor area
Side and rear setbacks of 4 feet are the same under both classes. The front setback is the number to check. Section 17.21.070 prints 25 foot front setbacks for a Class 2 unit, and we quote that as the code reads. It looks high against the 5 to 10 foot front yards that R-1 lots carry under 17.08.030, so do not treat it as a rule of thumb until Planning confirms how it applies to your lot.
The floor area ratio is the second squeeze. A Class 2 ADU may not push the lot above 50 percent, and lots of 2,100 square feet or less use the small-lot variations in 17.08.040, such as 70 percent lot coverage and 300 square feet of open space. Maximum height on R-1 lots is 25 feet, and the code measures it from a certified topographic survey, so the survey comes before the sketch.
Many buildings here no longer meet today's setback or parking rules. Chapter 17.52 limits how a nonconforming structure can change, so ask whether the house on the lot is one before you plan an attached unit. Which zone a lot sits in is on the City's zoning map, and the code text does not say which neighborhoods are R-1 or R-2.
Does an ADU in Hermosa Beach need coastal review? The Coastal Clearance step
Possibly, and it depends on the address. Roughly the western half of the city sits in the California Coastal Zone, based on a 92-point sample in which 44 points, 47.8 percent, fell inside the Commission's polygon. That is a sample, not a parcel map. Hermosa Beach has no certified Local Coastal Program, so the Coastal Act is the standard of review, and Chapter 17.78 requires a Coastal Clearance from Community Development before a permit issues for development in the zone.
The ADU chapter folds that step into the clock. If a Coastal Development Permit is needed, a complete application for it must be part of the ADU application, and the permit must be decided within 60 days. We could not read the exemption text, so we make no claim about which ADUs are exempt, and we leave coastal questions to the City.
The ground matters as well. The state seismic layer flagged 13 of 92 sample points, 14.1 percent, for liquefaction, and the County tsunami layer flagged 12, both on the beach side of town. The amended Residential Code also asks for a signed risk acknowledgment on structures with a portion below street grade, so a slab or a sunken garage floor needs a soils answer early.
Garage conversion ADU in Hermosa Beach: parking, the existing slab and the two-space rule
A garage conversion is the lightest-touch route on a built-out lot, and the Class 1 rules treat it that way: one converted ADU plus one junior ADU, inside existing space. No replacement parking is required for a garage or parking space that is demolished or converted. The catch is the base requirement. A one-family dwelling needs two off-street spaces plus one guest space under 17.44.020, so a lot that loses its garage may fall short of that rule even where the ADU itself owes nothing.
Class 2 parking is one off-street space per ADU or per bedroom, whichever is less, and it may sit in a setback or in tandem. Exceptions cover half a mile walking distance of public transit, a historic district, a unit that is part of the main house or an accessory structure, an area where on-street permits exist but are not offered to the occupant, and a car share stop within one block.
Section 17.44.120 asks for at least 6 inches of portland cement concrete under parking spaces and driveways, so inspect the existing slab for thickness, cracks and drainage before you price a conversion. Ask your engineer what the slab must carry once it becomes a bedroom floor.
Windows, screening and materials: the design standards for a Class 2 ADU
Class 2 units carry design rules of their own. Exterior materials, colors and roof slope must match the main house. Windows and doors may not have a direct line of sight to an adjoining residential property, and windows less than 30 feet from a lot line that is not on a street must be clerestory windows, with the bottom of the glass at least 6 feet above the floor, or use frosted or obscure glass.
Screening is required too: one 15-gallon plant per 5 linear feet of ADU wall, or one 24-inch box plant per 10 feet, at least 6 feet tall when planted, or a 6 foot solid fence. Plants come from the City's approved list and must be drought tolerant. An ADU on or within 600 feet of a California Register of Historic Resources property must not be visible from a public right of way. The Preservation Ordinance, Chapter 17.53, separately protects landmarks.
On a narrow lot those rules can decide the floor plan before the kitchen does, so draw the window wall first. The same privacy logic shows up on our Hermosa Beach window page.
ADU fees, utility connections and the fire protection fee in Hermosa Beach
Section 17.21.080 allows no impact fee for a junior ADU or an ADU under 750 square feet, and for a unit of 750 square feet or more any impact fee must be proportional to the main house floor area. A converted ADU on a single-family lot needs no new utility connection or capacity charge, while other units need a separate connection. The processing fee is set by council resolution, which we did not open, so no dollar amounts appear here.
The Fire Code amendment in 15.20.030 charges a fire protection improvement fee of $0.09 per square foot of net floor area for residential construction, paid before a building permit for any new structure or expansion. Whether it applies to an ADU was not confirmed, so ask the Building Official. Fire sprinklers are required in an ADU only when the main house needs them.
Use rules matter for budgets. ADUs may not be rented for fewer than 30 days or sold separately from the lot except as state law allows, and a junior ADU generally requires owner occupancy. Our ADU cost guide shows how the utility and soft-cost lines build up.
From application to final: the order of an ADU job in Hermosa Beach
Every ADU and junior ADU needs both an ADU permit and a building permit, reviewed without a hearing under 17.21.040. The City must say within 15 business days whether the application is complete and must approve or deny a complete one within 60 days. Section 17.60 gives a plain zoning clearance 15 days. The code mirror does not print a plan check time for the building permit itself, so ask for one.
Once permits issue, the site follows the City's rules: construction runs weekdays from 8:00 a.m. to 6:00 p.m. and Saturdays from 9:00 a.m. to 5:00 p.m., never on Sundays or national holidays. Every site needs 6 foot protective fencing with screening, and demolition, shoring or other work that may affect adjoining property needs 5 days of written notice to every owner and occupant within 100 feet. Debris is separated under Chapter 15.16.
MDG Builders, CSLB #1040337, is the general contractor on an ADU: we draw the unit, file the applications and schedule the trades, and licensed firms for grading, framing, plumbing and electrical build it. You can ask each firm for a license number and certificate of insurance. Contractors and subcontractors also need a Hermosa Beach business license before a building permit issues.
ADU photos from Hermosa Beach and nearby homes
ADU scenes tied to Hermosa Beach and the beach cities around it, from garage conversions and slabs to finished cottages. Tap a photo to enlarge it.
What adu construction costs around Hermosa Beach
Our ADU construction page shows roughly $100,000 to $200,000 for turning a garage into a studio or one-bedroom unit, and roughly $200,000 to $400,000 for building a new detached unit of 400 to 800 square feet. Three independent sources support those ranges: a UC Berkeley survey of Los Angeles County households that finished or applied for an ADU in 2018 and 2019, with a $100,000 median and $180,000 for detached units; the Terner Center's 2020 estimate of $148,000 for Los Angeles; and a 2025 job cost of $178,536 from Remodeling magazine's Cost vs. Value report. None is a Hermosa Beach quote, and a narrow beach lot with coastal review, soils work and tight access can run higher. The garage conversion guide and the ADU versus JADU guide go deeper. Neighboring cities apply the state law their own way, so compare ADU construction in Manhattan Beach, Redondo Beach, Torrance and Los Angeles. A bathroom inside the unit is on our Hermosa Beach bathroom page, a larger attached project on the Hermosa Beach room addition page, and the Hermosa Beach area page lists every trade we cover in the city.
| What it covers | Typical range |
|---|---|
| Garage conversion to a studio or one bedroom | $100,000 to $200,000 |
| New detached ADU, 400 to 800 sq ft | $200,000 to $400,000 |
| UC Berkeley survey, Los Angeles County median, 2018 and 2019 projects | $100,000 overall. $90,000 garage. $180,000 detached. |
| Terner Center and Berkeley CCI, 2020 | $148,000 Los Angeles estimate. $167,000 statewide average. |
| Remodeling Cost vs. Value 2025, Los Angeles | $178,536 job cost |
| Electrical and plumbing, Angi Los Angeles, January 2026 | Electrical $2,600 to $7,800. plumbing $3,900 to $10,400. |
| City permit and plan check fees | Not priced here |
Other work we manage in Hermosa Beach
Hermosa Beach ADU questions, answered
Can I build an ADU in Hermosa Beach?
Yes. Chapter 17.21 of the Municipal Code allows ADUs and junior ADUs and reviews them without a public hearing, though a building permit is also required. We read the chapter on a code mirror, so ask Planning for the current standards and the application checklist before you draw anything.
How big can an ADU be in Hermosa Beach?
Under the code as printed, a Class 1 detached unit may be up to 800 square feet, and a Class 2 unit up to 850 square feet for a studio or one bedroom and 1,000 for two or more bedrooms. Floor area ratio, height and setbacks also limit what fits. Confirm the numbers with Planning.
How much does it cost to build an ADU in California?
Our working figures are about $100,000 to $200,000 for a garage conversion and about $200,000 to $400,000 for a new detached unit of 400 to 800 square feet. The inputs are surveys from 2018 to 2020 and one 2025 job cost, and none covers Hermosa Beach, so only a written proposal after a site visit gives a real figure.
Do I need to provide parking for my ADU?
Sometimes. A Class 2 unit needs one off-street space per ADU or per bedroom, whichever is less, with exceptions near transit, in a historic district, inside an existing structure, or within one block of a car share stop. No replacement is required for a converted garage, but the house itself still owes its base spaces.
What is the difference between an ADU and a JADU?
An ADU is a full independent unit that can be attached or detached, while a junior ADU is a small unit made from space inside the house. Hermosa Beach lets a junior ADU share a bathroom with the main house if it has an interior entrance, and generally requires owner occupancy for it.
Can I rent out my ADU or sell it separately?
You can rent it, but not for fewer than 30 days, and it generally cannot be sold apart from the lot except as state law allows. A junior ADU generally requires the owner to live on the property. Short-term rental rules are separate, and we did not research them for this page.
How long does it take to get an ADU permit?
The City must tell you within 15 business days whether the application is complete, then decide within 60 days of a complete one, and the coastal permit, if needed, runs inside that same 60 days. We found no published plan check time for the building permit, so ask the City for its current figure.
Do I need a permit to convert my garage into an ADU?
Yes. A converted garage becomes a dwelling unit, and chapter 17.21 requires both an ADU permit and a building permit for every ADU. Work started before a permit issues can be charged up to four times the normal permit fee under 15.02.080, so wait for the permit before you demolish anything.
Tell us about your Hermosa Beach ADU plans
Tell us the lot size, whether you are weighing the garage or the back yard, how old the house is and which part of town you are in, and we will plan the first visit around the setback and coastal questions.