ADU Constructionin Alhambra, CA
ADU construction in Alhambra goes through a ministerial building permit review, decided within 60 days of a complete application, with no separate Planning hearing. The October 2026 Zoning Code guarantees an 800 square foot unit with 4 foot side and rear setbacks, and a garage conversion needs no replacement parking.
Alhambra's lots are a natural fit for a second unit. The Census Bureau's 2020 to 2024 estimates count 41.3 percent of the city's 32,751 homes as detached houses, put the median owner-occupied home value at $857,800 and show 49.5 percent of the housing built before 1960, so many backyards hold an older garage that a conversion would reuse.
This page covers the process the City actually runs, the size and setback limits in its new Zoning Code, garage conversions, site work, listed fees and rental rules. Cost ranges and the phase timeline sit on our ADU construction page.
Alhambra Planning and Building rules that apply to an ADU
Where adu construction permits come from in Alhambra: City of Alhambra Community Development Department, Building Division.
- Alhambra reviews ADU and JADU building permits ministerially: within 60 days of a complete application (30 days for a detached ADU on a pre-approved plan), with a completeness notice within 15 business days. No separate Planning application is needed, but tree removal permits, grading permits and the other building permit requirements still apply, and denials or completeness decisions can be appealed to the Planning Commission (AMC 23.22.040.M).
- On a lot with a single-unit dwelling, Alhambra allows one ADU within existing or proposed space, one new detached ADU and one JADU. On multi-unit lots it allows up to 2 detached ADUs with a proposed multi-unit building or up to 8 with an existing one (not more than the number of units), plus conversion ADUs in non-livable space capped at 25 percent of existing units (23.22.040.C).
- Size limits in 23.22.040.D: a detached ADU on a single-unit lot up to 1,200 square feet, a detached ADU on a multi-unit lot 850 square feet (1 bedroom or less) or 1,000 square feet (more than 1 bedroom), an attached ADU up to 50 percent of the main dwelling or 850 or 1,000 square feet, whichever is greater, and a JADU up to 500 square feet. The code guarantees an 800 square foot ADU with 4-foot side and rear setbacks regardless of lot coverage, floor area ratio, open space or front setback limits.
- ADU setbacks and height: 4 feet minimum at the side and rear for new attached or detached ADUs, no setback for an ADU in existing living area or an existing accessory structure or rebuilt in the same location and dimensions (if fire and safety allow), 5 feet eave to eave between buildings, 2 stories and 25 feet maximum height, and an ADU placed in front of the main dwelling must meet the zone's front setback.
- A new ADU must use the same exterior materials, roof covering, colors and architectural details as the main dwelling unless it is built from a City pre-approved plan or qualifies under Government Code 66323 (23.22.040.E.8). ADUs and JADUs may not be used as short-term rentals under Chapter 5.92.
- ADU parking is one open or enclosed space, tandem on an existing driveway allowed, but none is required within half a mile of a public transit stop, on a parcel on a historic register, for an ADU within the existing home or an existing accessory structure, where on-street permits are required but not offered to the occupant, within one block of a car-share hub, or for a 66323 unit. Replacement parking is not required when a garage or carport is converted or demolished for an ADU (23.22.040.G).
- There is no owner-occupancy requirement for an ADU. For a JADU either the JADU or the main home must be owner-occupied unless it has its own sanitation facilities, and a deed restriction must be recorded with Los Angeles County before occupancy (23.22.040.H). Impact fees cannot be imposed on an ADU of 750 square feet or less, and the City may not deny a permit for certain unpermitted ADUs built before January 1, 2020 (23.22.040.J and N).
- The City's ADU guide says an ADU building permit is applied for in the Permit Portal as an ADU Permit (each detached ADU needs its own permit, and an address assignment application is also required), then the plans go in GoPost; the first review takes 2 to 4 weeks, with the Building Division reviewing on behalf of Public Works, Planning and Fire and Utilities reviewing at the same time. Los Angeles County Sanitation District approval and fees, and Alhambra Unified School District fees for new ADUs and for conversions of 500 square feet or more, must be paid before permit issuance.
Sources for these rules
How do you build an ADU in Alhambra? Permit Portal, plan check and a 60 day clock
Alhambra reviews ADU and junior ADU building permits ministerially, which means the City checks the plans against objective standards without a hearing. It has 60 days from a complete application to act, or 30 days for a detached ADU built from a City pre-approved plan, and it owes you a completeness notice within 15 business days. We found no list of the City's pre-approved plans, so ask Planning whether one fits your lot.
No separate Planning application is needed for the ADU itself. You apply as an ADU Permit in the Permit Portal, each detached unit gets its own permit plus an address assignment application, and the plans go into the plan check portal. First review takes 2 to 4 weeks, with the Building Division reviewing for Public Works and Planning while Fire and Utilities review at the same time. A denial or an incomplete notice can be appealed to the Planning Commission under AMC 23.22.040(M).
State law backs the clock: Government Code section 66317 requires approval or denial within 60 days and treats silence as approval. The Planning Division still confirms zoning first, and the City's ADU page lists the forms. Our guide to ADU versus JADU rules explains the two unit types.
How big can an ADU be in Alhambra, and how close to the fence can you build?
On a lot with one house, the October 2026 code allows a detached ADU up to 1,200 square feet. An attached ADU can reach 50 percent of the main dwelling or 850 square feet for one bedroom or 1,000 for more, whichever is greater, and a junior ADU stops at 500 square feet. The code also guarantees an 800 square foot ADU with 4 foot side and rear setbacks regardless of lot coverage, floor area ratio, open space or front setback limits.
New attached or detached units need 4 feet at the side and rear and 5 feet eave to eave from other buildings, and they top out at 2 stories and 25 feet. A unit placed in front of the main house must meet the zone's front setback. Converting existing living space or an existing accessory structure needs no new setback, and a rebuild on the same footprint keeps its old one if fire and safety allow.
A new ADU must match the main house in exterior materials, roof covering, colors and architectural details unless it comes from a City pre-approved plan or qualifies under Government Code section 66323. Parking is one space, tandem on an existing driveway allowed, and none is required in a long list of cases, including a lot within half a mile of a public transit stop and a parcel on a historic register.
Garage conversion ADU in Alhambra: change of use, fire walls and escape windows
Converting a permitted garage is a change of use from U to R-3, so the space has to meet current code for fire-resistant construction, light, ventilation, heating, ceiling height, bathroom space, egress and alarms, according to the City's ADU guide. Replacement parking is not required when a garage or carport is converted or demolished for an ADU, which answers the question that stops most owners.
The guide's wall rules are specific. A non-sprinklered conversion wall less than 5 feet from the property line, or less than 3 feet if sprinklered, must be 1-hour fire-resistance rated, no openings are allowed in exterior walls less than 3 feet from the line, and openings between 3 and 5 feet are limited to 25 percent of the wall area. A sleeping room needs an emergency escape opening that is at least 24 inches high and 20 inches wide.
If the slab has no vapor retarder, the guide lists approved alternate membranes, and each dwelling unit needs its own heating unit. In a garage from the era of the city's 1960 median year built, we check the slab and footings before promising a floor plan. Our garage conversion permit steps post walks through a Los Angeles version of the sequence.
Build an ADU in Alhambra: grading, utilities, sewer approval and protected trees
A new detached ADU brings site work that a conversion avoids. The City's guide requires a separate grading and drainage plan and permit when 50 cubic yards or more of earth is moved, or when an excavation leaves a slope over 5 feet high and steeper than 2 to 1, and the building permit cannot issue until Planning approves and stamps those plans. Whether a lot crosses that line depends on footing and trench depths, so we measure before we say so.
Utilities come next. The guide says Los Angeles County Sanitation District approval and fees, plus Alhambra Unified School District fees for new ADUs and for conversions of 500 square feet or more, must be paid before the permit issues. The state's HCD ADU handbook adds that a newly built detached ADU needs solar panels under the Energy Code, while conversions and additions do not.
Trees are the other site question. Under the October 2026 code, protected trees must be preserved in place for an ADU unless an arborist report and replacement are provided: two 24-inch box trees per 10 inches of trunk for oaks and California natives, one per 10 inches for mature trees, with at least half planted on the site. A slab edge or trench that crowds an oak can turn into a tree permit.
ADU on an older Alhambra lot: historic review, matching the house and the old garage
Alhambra grew fast in the 1920s: the Census counts 9,096 residents in 1920 and 29,472 in 1930, and the Historical Society places Arts and Crafts, Spanish and storybook houses in tracts such as Ramona Park, Wuest-Bushnell and Lindaraxa. If your lot has an older detached garage, that structure is what a conversion would reuse, and its age is the first thing we check.
The City's survey flagged 865 properties as potentially eligible for historic listing and formally designated none, according to the City's page. An ADU on a parcel on a historic register needs no parking, and the new unit still has to match the main house in materials, roof and colors, which on a Craftsman or Spanish house is a design job, not a default.
We did not check which individual properties sit on the City's inventory, so ask Planning about yours before drawing. A potentially eligible house needs a historic resource assessment by a qualified professional if review is triggered, and the Historic Preservation Commission can delay demolition of a historic resource for up to 180 days. A backyard unit that leaves the street-facing house alone is a different question from an addition to it.
ADU fees in Alhambra: what the City's guide lists and why to confirm each amount
State law bars impact fees on an ADU of 750 square feet or less, and on a junior ADU of 500 square feet or less, under Government Code section 66311.5, and the City's code repeats the 750 square foot line. Utility connection charges are separate from that exemption.
The City's ADU guide lists dollar amounts, but it is undated and still cites the 2019 codes, so treat each as a 2019-era figure to confirm: Public Works plan check $120.25, Fire plan check $293.46, Planning plan check $120.00, Utilities plan check $69.00, address assignment $124.33 per building, a $2,000 new construction tax per new unit, a $73.98 issuance fee per permit, a General Plan fee of 0.5 percent of valuation with a $30 minimum and a plan maintenance fee of 2 percent of permit fees. The utilities improvement charge is $448 without a new water meter and $7,222 with one.
Three amounts are missing from that list: the building permit and plan check fees, which follow project valuation, the Sanitation District charge and the school district fee. The district's 2025 worksheet on the City's forms page is a scanned image we could not read, so we print no school fee and no permit fee, and the proposal lists what the counter quotes for your address.
Renting an ADU in Alhambra: owner occupancy, short-term rentals and fire sprinklers
No owner-occupancy requirement applies to an ADU. A junior ADU needs either the unit or the main home to be owner-occupied unless the JADU has its own sanitation facilities, and a deed restriction must be recorded with Los Angeles County before anyone moves in. State law lets a city require rental terms of 30 days or longer.
Alhambra bars using an ADU or JADU as a short-term rental under Chapter 5.92 of its code, so the Airbnb question has a clear local answer. A long-term tenant is the legal use, and with 58.9 percent of the city's households renting, that is a familiar arrangement here. We found no Alhambra rent study and print no income estimate.
Fire sprinklers are required in the ADU only if the main dwelling must have them, under section 23.22.040.I of the October 2026 code. The City's older ADU guide reads differently on sprinklers, so we ask the Building Division which standard it applies to your plans. An ADU cannot be sold apart from the main house except through the state's limited exceptions in Government Code sections 66341 and 66342.
MDG Builders, CSLB #1040337, designs, permits and manages the job as a general contractor, and licensed subcontractors do the trade work. You can ask to see each license and insurance certificate.
ADU photos from Alhambra and nearby homes
ADU scenes tied to Alhambra tracts and neighboring communities, from slab and framing to finished interiors. Tap a photo to enlarge it.
What adu construction costs around Alhambra
Our ADU construction page puts a garage conversion to a studio or one-bedroom at about $100,000 to $200,000 and a new detached unit of 400 to 800 square feet at about $200,000 to $400,000. Those ranges rest on a 2021 UC Berkeley survey of 2018 and 2019 projects, a 2020 Terner Center estimate and the 2025 Cost vs. Value report for Los Angeles, which lists $178,536 for its reference unit and 39.9 percent recouped. Construction costs have climbed since the surveys, and we found no Alhambra price study, so the written proposal sets the real figure with agency fees on their own lines. Read our ADU cost guide for the drivers, or weigh a unit against more rooms with the room addition vs ADU guide. Rules differ across the city line, so compare ADU construction in Pasadena, El Monte, Glendale and Los Angeles. A new unit often pairs with a bathroom remodel in the main house or a room addition, and our Alhambra overview lists every local page.
| 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 |
Alhambra ADU questions, answered
How do I build an ADU in Alhambra, step by step?
Start with Planning to confirm what the lot allows, then draw plans, apply for an ADU Permit in the online Permit Portal, upload the plans to the plan check portal, answer any correction notice and pay the agency fees. Build through portal-scheduled inspections and finish with the final. Each detached unit gets its own permit and an address assignment application.
How long does it take to get an ADU permit?
Alhambra has 60 days to act on a complete application, or 30 days for a detached ADU on a City pre-approved plan, after a completeness notice due within 15 business days. The first plan check review takes 2 to 4 weeks. Design time before filing and agency approvals such as the Sanitation District add to that, so the full path runs longer than 60 days.
How big can an ADU be in Alhambra?
A detached ADU on a single-house lot can reach 1,200 square feet. An attached ADU can reach 50 percent of the main home or 850 to 1,000 square feet, whichever is greater, and a junior ADU is capped at 500 square feet. The code also guarantees an 800 square foot unit with 4 foot side and rear setbacks, whatever the lot coverage.
Can I convert a garage to an ADU?
Yes, a permitted garage can become an ADU. It counts as a change of use from U to R-3, so the space must meet current code for fire resistance, light, ventilation, heating, ceiling height and egress, and a wall close to the property line may need a 1-hour rating. Alhambra does not ask for the garage parking to be replaced.
Do I need to provide parking for my ADU?
Usually one space, but none is required in many cases. Exemptions include a lot within half a mile of a public transit stop, a parcel on a historic register, a unit inside the existing home or an accessory structure, and a unit where on-street permits are required but not offered to the occupant. Tandem parking on an existing driveway counts.
Do I need to live on the property to build or rent an ADU?
No, not for an ADU. Alhambra sets no owner-occupancy requirement for ADUs. A junior ADU is different: either the JADU or the main home must be owner-occupied, unless the JADU has its own bathroom and sanitation facilities, and a deed restriction is recorded with Los Angeles County before occupancy.
Can I rent my ADU on Airbnb or only for long-term rentals?
Only long term. Chapter 5.92 of Alhambra's code bars using an ADU or JADU as a short-term rental, and state law lets a city require rental terms of 30 days or longer. Confirm the current wording with the City before you build a financing plan around rental income.
How much does it cost to build an ADU in Los Angeles County?
Expect roughly $100,000 to $200,000 for a garage conversion and $200,000 to $400,000 for a new detached ADU of 400 to 800 square feet, based on county studies and the 2025 Cost vs. Value report. Those are regional ranges, not Alhambra quotes, and the City's agency fees appear as separate lines in a written proposal.
Can I sell my ADU separately from the main house?
Generally no. State law bars selling an ADU apart from the main house, with two exceptions: a qualified low-income buyer through a qualifying nonprofit under Government Code section 66341, or a city-adopted condominium ordinance under section 66342. We did not confirm that Alhambra has adopted a condominium ordinance, so ask Planning.
Tell us about your Alhambra ADU
Share the street, whether you want a garage conversion or a new backyard unit, the age of the existing garage and house, and any trees near the build area, and we will prepare for the site visit.