ADU Constructionin Calabasas, CA
ADU construction in Calabasas starts with state law, because HCD found the City's 2020 ADU ordinance out of compliance in 20 numbered ways on May 4, 2026. State law sets a 60 day review clock, 4 foot setbacks and an 800 square foot floor. City rules may differ or have changed, so confirm with Planning before you draw.
About 60 percent of Calabasas homes, 5,617 of 9,431, are detached single-family houses, and 38.2 percent were built before 1980. The city incorporated on April 5, 1991, and the median owner-occupied home is valued at $1,504,500. Lots that large in value make a backyard unit a serious option, but the rulebook behind it has been shaky since the state's housing department wrote to the City.
This page covers which rules apply, how to build an ADU step by step, garage and pool house conversions, size and the SB 9 alternative, oaks and canyon overlays, hillside and fire limits, and fees. The City's website and the official code site refused our tools, so the Municipal Code text comes from a third-party mirror, and we could not confirm whether the City has adopted a new ADU ordinance since May 2026. Price ranges and phases are on our ADU construction page.
Calabasas Planning and Building rules that apply to ADU construction
Where adu construction permits come from in Calabasas: City of Calabasas Community Development Department, Building and Safety Division.
- California HCD's letter of May 4, 2026 reviewed Calabasas ADU Ordinance 2020-382 and found it fails to comply with state ADU law in 20 numbered findings, including the zoning clearance requirement, the ban on separate sale, size as a percentage of the main house, the 16 foot height cap, the design conformance rule, the missing appeal right and the missing parking exception for ADUs built with a new home, and it asked the City for a written response by June 3, 2026, either amending the ordinance or adopting it with findings that explain why it complies. State law therefore governs where the two conflict, and any written ADU page must tell readers to confirm the rules in force.
- HCD's earlier technical assistance letter (December 5, 2025) said the ordinance on file for Calabasas dates from 2020 and may be outdated, and that under the 2025 ADU Handbook a homeowners association cannot influence the approval of an ADU application and an ADU cannot carry a deed restriction. The letter also says that, as of 2025, owner occupancy is required for a JADU that shares sanitation facilities with the main house and not for a JADU with its own.
- Municipal Code 17.12.170, as last amended by Ordinance 2020-382, allows one ADU or one JADU on a legal lot in the RS, RM, RR, HM, RC, PD and OS zones subject to a zoning clearance. The text sets 4 foot side and rear setbacks, a 10 foot gap to the main dwelling for a detached unit, a 16 foot one-story limit for a detached unit, a 220 square foot minimum, a 500 square foot JADU limit, and a 1,200 square foot or 50 percent of the main house limit for an attached unit, and several of these are the items HCD flagged.
- The same section lets one ADU be built entirely inside the existing building envelope of a legal house or accessory structure (with up to a 150 square foot addition for access) with exterior access independent from the house, and lets an ADU of 800 square feet or less, no taller than 16 feet and with at least 4 foot side and rear setbacks go ahead despite the size and coverage table.
- Under Municipal Code 17.12.170(F) the community development director reviews an ADU application ministerially within 60 days of a complete submission, 17.12.170(H) says no development impact fees apply to an ADU under 750 square feet and larger ADUs pay proportionally, and utility connection and capacity fees are not charged for an ADU unless it is built with a new home. Parking is one extra space with listed exceptions (half mile of transit, existing structure, historic district, permit parking not offered, car share).
- Short-term and transient rental of an ADU for less than 30 days is prohibited (Municipal Code 17.12.170(C) and 17.12.175), and the code says an ADU cannot be sold separately from the primary dwelling, a rule HCD says conflicts with the state's limited separate-sale allowance.
- Chapter 17.84 (Ordinance 2022-398) sets a ministerial design review permit for SB 9 projects on RS, RR and RC parcels, limited to no more than two units of 800 square feet or less each, not in a historic district or on a historic resource, with drawings by a licensed architect, exterior materials, colors, windows and roofing matching the existing home, no roof decks, a new or separate utility connection and undergrounded services, and a shadow study if a neighbor has solar.
- In the Old Topanga and Calabasas Highlands overlay zones, the ADU table says ADU additions and freestanding ADUs must comply with the zoning code standards for those overlays (Table 2-4 in Municipal Code 17.12.170).
What does HCD's May 2026 letter mean for an ADU in Calabasas?
It means state law controls wherever the City's ordinance disagrees with it. California's housing department, HCD, wrote on May 4, 2026 that Ordinance 2020-382 fails state ADU law in 20 numbered findings. They include the zoning clearance requirement, the ban on separate sale, size as a percentage of the main house, the 16 foot height cap, the design conformance rule, the missing right to appeal and the missing parking exception for an ADU built with a new home. HCD asked for a written response by June 3, 2026, either amending the ordinance or adopting it with findings that explain why it complies.
An earlier technical assistance letter, dated December 5, 2025, said the ordinance on file dates from 2020 and may be outdated. It added that, under the 2025 ADU Handbook, a homeowners association cannot influence approval of an ADU and an ADU cannot carry a deed restriction.
Search results mention Planning Commission notices in 2026 about rescinding and replacing Section 17.12.170, but we did not open them or find a Council vote. Treat any number from the old ordinance as a possible former rule, and ask Planning what it applies today.
How to build an ADU in Calabasas, from site check to building permit
Start with the lot. The code text allows one ADU or one junior ADU on a legal lot in the RS, RM, RR, HM, RC, PD and OS zones, and most single-family lots are RS, but RR, RC and the canyon overlays change the numbers, so confirm your zoning. Then draw a site plan with every structure, easement and oak.
The review clock comes from the state. Government Code section 66317 gives the City 15 business days to say whether an application is complete and 60 days after that to approve or deny, with a denial listing every defect; silence past 60 days means deemed approval. The code text has the community development director reviewing ministerially within 60 days, which matches. HCD still listed the zoning clearance step among its findings, so ask Planning what, if anything, it requires first.
After approval comes the building permit, inspections and a certificate of occupancy that cannot precede the main house's. We found no City ADU web page we could read, so the application packet, fee table and plan check times are all unconfirmed.
- Is the lot in the RS zone, or in an RR, RC or overlay area?
- Which structures, trees and utility lines will the survey show?
- Does Planning still require a zoning clearance for an ADU?
Garage, workshop or pool house: converting existing space to an ADU
A conversion is the most protected route. State law requires a city to approve an ADU and a junior ADU created inside an existing house or accessory structure such as a garage, with up to 150 square feet added only for entry and exit, and it allows no replacement parking when a garage is converted. The City's code text lists parking exceptions that include existing structures and half a mile from transit.
Calabasas adds a rule for the building that already stands. Section 17.12.170(E) calls for a safety inspection by the building official and the fire department when an unpermitted structure becomes an ADU, and the applicant must fix items such as a 7 foot ceiling, light and ventilation in each habitable room, hot water to the kitchen and bath, a strapped and vented water heater and a sewer connection. State law limits when a city can deny a pre-2020 unpermitted ADU, so ask Planning which path your room fits. Our guide to garage conversion permit steps shows the sequence in Los Angeles.
A pool house or studio needs a warning. Section 17.12.165(M) bars a kitchen in an accessory workshop, studio or pool house, so a kitchen there makes it a second dwelling that has to qualify as an ADU or junior ADU.
How big can an ADU be in California, and is SB 9 an alternative in Calabasas?
State law caps a city's minimum at 800 square feet with 4 foot side and rear setbacks, and no city may set a maximum below 850 square feet, or 1,000 if the unit has more than one bedroom. A detached unit may go up to 1,200 square feet. The City's code text uses its own limits, including a percentage of the main house for attached units, and HCD listed that as a finding, so we do not state the local numbers as current.
A junior ADU is capped at 500 square feet inside the single-family house, and per HCD's December letter owner occupancy applies only when it shares sanitation with the main house. Short-term rental of an ADU under 30 days is barred in the code text (17.12.170(C) and 17.12.175), and state law lets a city require rentals longer than 30 days.
Chapter 17.84, adopted as Ordinance 2022-398, adds a ministerial design review for SB 9 projects on RS, RR and RC parcels: no more than two units of 800 square feet or less each, not in a historic district, drawings by a licensed architect, matching materials, no roof decks and undergrounded services. Whether SB 9 or an ADU fits better depends on the lot, and our ADU versus JADU guide compares the unit types.
Oak trees and canyon overlays: what can stop an ADU before a building permit
In Old Topanga, Calabasas Highlands and Park Moderne, a detached ADU of 400 square feet or more of habitable area counts as a major construction project, which needs a Public Works encroachment permit before the building permit can issue (Municipal Code 17.18.020(E) and 17.90.020). The code limits active encroachment permits to three at a time in each overlay. The ADU table also says freestanding ADUs and additions in Old Topanga and Calabasas Highlands must meet those overlays' zoning standards. State law allows only objective standards, so ask the City how the two fit together.
Oaks come next. Section 17.32.010 requires a permit to alter any oak or scrub oak habitat, and the director can approve an encroachment of up to 10 percent of a protected zone, such as a fence or a trench. Larger work goes to the Planning Commission with an arborist's report, mitigation can run to one inch of new oak for each inch removed with five years of monitoring, and a violation can bring a stop-work order and a building moratorium of up to 10 years that follows the property.
So walk the lot with the oaks mapped before you place the unit, because the location decides whether a hearing is needed.
Building an ADU on a Calabasas slope in a Very High fire hazard zone
Hillside rules apply on any site over 10 percent slope or with a ridgeline (Section 17.20.150), with graduated grading limits and fire-retardant roofing. On a lot averaging 20 percent slope or more, Section 17.20.140(D) limits total building height to 15 feet, which sits below the state's 16 foot floor for detached ADUs. We did not research which controls, so put the question to Planning in writing.
Fire is the other filter. The County's GIS copy of CAL FIRE's map returned Very High at 95 of 99 sample points across the city, a sample and not a parcel check. Development within 500 feet of native vegetation must meet with the County Consolidated Fire District before a building permit for a new occupied structure under Section 17.20.130. State law bars an ADU from triggering sprinklers in the main house, and from needing them itself if the main house has none.
Soils matter too. In the same sample, 10 of 99 points fell in state-mapped liquefaction zones and 45 of 99 in earthquake-induced landslide zones, so a soils report is likely on a slope. Section 17.20.130 asks for site-specific soils studies with new development permits.
ADU fees, utilities and construction hours in Calabasas
State law exempts an ADU of 750 square feet or less from impact fees, and larger units pay in proportion to the main house. The code text agrees (17.12.170(H)) and adds that utility connection fees are not charged unless the ADU is built with a new home. The state treats connection and capacity charges as separate from the impact fee exemption, so ask the water and sewer districts. School fees can apply above 500 square feet.
A new detached ADU must carry solar under the Energy Code, but a conversion or addition does not, per HCD's handbook. Chapter 8.28 makes the owner certify stormwater controls before a building or grading permit issues, keeps soil piles bermed or covered from October 1 to April 15 and bars concrete wash water from the storm drain. Construction runs 7 a.m. to 6 p.m. weekdays and 8 a.m. to 5 p.m. Saturday, never on Sundays or federal holidays (17.20.160(C)).
MDG Builders, CSLB #1040337, designs the unit, handles the permits and manages the schedule, while licensed firms do the foundation, framing, plumbing and electrical work and each one's license and insurance certificate is yours to request.
ADU photos from Calabasas and nearby homes
ADU scenes tied to Calabasas and the communities around it, from garage conversions and slabs to finished studios. Tap a photo to enlarge it.
What adu construction costs around Calabasas
Budget about $100,000 to $200,000 for a garage conversion to a studio or one bedroom and about $200,000 to $400,000 for a new detached unit of 400 to 800 square feet, the ranges on our ADU construction page. Three independent reads support those ranges: the UC Berkeley survey of Los Angeles County ADUs finished or applied for in 2018 and 2019 (median $100,000, garage units $90,000, detached units $180,000), the Terner Center's 2020 estimate of $148,000 for Los Angeles, and Remodeling magazine's 2025 Cost vs. Value job cost of $178,536, with 39.9 percent recouped at resale. None is a Calabasas quote, and grading, oak work, fire-hardening and soils reports on a canyon lot can add lines that a flat Los Angeles lot would not have. We could not read the City's fee schedule, so permit and plan check fees appear as separate lines in a written proposal. The ADU cost guide covers the details. Neighboring cities apply the same state law their own way, so compare ADU construction in Santa Monica, Santa Clarita, Burbank and Los Angeles. A bathroom in the unit is on our Calabasas bathroom page, a larger attached addition on the Calabasas room addition page, and the Calabasas 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 |
Calabasas ADU questions, answered
Can I build an ADU in Calabasas?
Yes, state law lets you build an ADU on a residential lot with an existing home, and the City's code text allows one in its residential zones. HCD found the City's 2020 ordinance out of compliance in May 2026, so state law controls where they differ. Confirm today's local rules with Planning before you hire a designer.
How big can an ADU be in Calabasas?
State law protects an 800 square foot detached ADU with 4 foot setbacks, allows detached units up to 1,200 square feet and bars a city from setting a maximum below 850 square feet. The City's own size limits were among HCD's findings, so ask Planning what applies. Hillside and overlay lots may add limits.
How much does it cost to build an ADU in California?
A garage conversion lands near $100,000 to $200,000 and a new detached unit of 400 to 800 square feet near $200,000 to $400,000 in our sourced ranges. Those rest on 2018 to 2020 surveys and a 2025 job cost from elsewhere in Los Angeles County, so only a written proposal after a site visit gives a Calabasas figure.
Do I need to provide parking for my ADU?
Often not. State law asks for no more than one space per ADU or per bedroom, bars replacement parking when a garage is converted, and requires none within half a mile of transit, in a historic district or when the ADU sits inside existing space. HCD flagged a missing parking exception in the City's ordinance.
What is the difference between an ADU and a JADU?
An ADU is a complete unit with its own kitchen and bathroom, attached or detached, while a junior ADU is up to 500 square feet carved from inside the house, with an efficiency kitchen and a separate entrance. A JADU may share a bathroom with the main house, and then owner occupancy applies.
Can I sell my ADU separately from my main house?
Generally no. State law bars separate sale except through a qualifying nonprofit buyer program or a city-adopted condominium ordinance. The City's code also bans separate sale, and HCD said that rule conflicts with the state's limited allowance. Ask a real estate attorney and Planning before you build for resale.
Can I rent my ADU on Airbnb or only long term?
Only long term in Calabasas, as the code text reads. Municipal Code 17.12.170(C) and 17.12.175 prohibit short-term and transient rental of an ADU for less than 30 days, and state law lets a city require terms longer than 30 days. No owner occupancy may be required for an ADU.
How long does it take to get an ADU permit?
The state clock is 15 business days for a completeness check and 60 days to approve or deny a complete application, with deemed approval if the City is silent. We found no published Calabasas time for building plan check, so we do not promise one. Oak, overlay or soils reviews can add time.
Can my HOA stop me from building an ADU?
Not by itself. HCD's letters say that under the 2025 ADU Handbook a homeowners association cannot influence approval of an ADU, and HCD's handbook says covenants that effectively prohibit or unreasonably restrict one are void. Reasonable architectural rules may still apply. Read your CC&Rs and ask HCD or an attorney if a board objects.
Do I need a permit to convert my garage into an ADU?
Yes. A garage that gains a kitchen and bathroom becomes a dwelling and needs a building permit with plumbing, electrical and mechanical inspections. In Calabasas an unpermitted structure also needs a safety inspection by the building official and the fire department before it can become an ADU.
Tell us about your Calabasas ADU plans
Tell us the neighborhood, whether you are weighing the garage or the backyard, how steep the lot is and where the oaks stand, and we will plan the first visit around the City's rules and state law.