Where we build · Altadena
Your ADU builder in Altadena
We were building steel-framed ADUs in Altadena before the Eaton fire, and one of ours survived it. Here is what we build here, how permitting works in an unincorporated community, and what the fire-rebuild rules mean for your lot.
Last updated July 2026 · Reviewed by Richard Corral, ADU Concepts · Licensed California general contractor (CSLB #1018294)
ADU Concepts is a licensed general contractor (CSLB #1018294) that designs and builds ADUs in Altadena. Because Altadena is unincorporated Los Angeles County, your permits run through the county, not a city hall, and we manage that process. State law allows up to three accessory units on a single-family lot, and on Eaton fire rebuild lots an ADU can receive its certificate of occupancy before the main house. We have built here: a steel-framed ADU we completed on Palm Street survived the Eaton fire.
We've built here
The ADU on Palm Street that survived the Eaton fire
About four years before the fire, we designed and built a 1,200 square foot ADU at a property on Palm Street in Altadena. When the January 2025 Eaton fire swept the neighborhood and the main residence on the property was lost, the ADU we built survived. It is one of the clearest examples we have of what light-gauge steel construction can mean for a family in a high fire risk area.
We say this carefully: no construction method makes a building fireproof, and every fire behaves differently. But a non-combustible steel frame, and the details that come with building for California conditions, gave this building a real chance, and it came through.
We also have an active single-family project on West Las Flores Drive in Altadena, and completed projects across Los Angeles County.
Our crews setting a panelized steel ADU frame on a Los Angeles County build.
Rebuilding after the Eaton fire? An ADU can come first.
Thousands of Altadena families are rebuilding. If your lot is one of them, state law now works in your favor: under AB 462, on lots covered by the Governor's disaster declaration, the county can issue a certificate of occupancy for a new ADU before the rebuilt main house receives its own. In practice, that means a family can build the ADU first, move in, and live on their own property while the main home goes up, instead of paying rent somewhere else for the length of the rebuild.
We design the ADU and the rebuild sequence together, and because our ADUs are panelized steel erected on site, the structure goes up quickly once the foundation is in. Framed in non-combustible light-gauge steel as standard, at no upcharge.
How ADU permitting works in Altadena
The single most important thing to know: Altadena has no city government, so the rules and the counter are Los Angeles County's. Here is what that means for your project.
Your permits go through LA County, not a city hall
Altadena is an unincorporated community, so there is no Altadena city government. ADU planning review runs through Los Angeles County, and your plans are checked and inspected by county Building and Safety. We manage that process for you, the same way we handle each city's process elsewhere.
State law sets the clock, everywhere in California
Since January 2026, the county must confirm within 15 business days that your ADU application is complete, and must approve or deny it within 60 days. If it misses that window, the ADU is deemed approved. ADU approval is ministerial: no hearings, no discretionary review.
Fire rebuild lots got a special ADU rule in 2025
Under AB 462, on lots covered by the Governor's disaster declaration, which includes Eaton fire lots, the county can issue a certificate of occupancy for a new ADU before the rebuilt main house gets its own. Families can live on their property in the ADU while the main home is still under construction.
What you can build on an Altadena lot
State ADU law applies in unincorporated LA County the same way it does statewide. On a single-family lot you can add up to three accessory units as of right: one ADU converted from existing space, one Junior ADU within the main house, and one new detached ADU of up to 800 square feet. A single detached ADU can reach 1,200 square feet under the statewide default, with 4-foot side and rear setbacks. There is no owner-occupancy requirement for a standard ADU.
Multifamily properties in Altadena have their own track: up to 8 new detached ADUs, capped at the number of units already on the lot, plus interior conversions of non-livable space.
What an ADU costs in Altadena
Altadena pricing follows our Southern California ranges: construction alone starts from about $172,000 for a compact studio, and most one or two bedroom backyard ADUs land in roughly the $290,000 to $410,000 range including design, engineering, and permitting. County fees, utility runs, and site conditions on your specific lot are budgeted separately, and hillside and fire-rebuild lots deserve a real site walk before anyone quotes you a number.
FAQ
Altadena ADU questions
Who issues ADU permits in Altadena?
Los Angeles County. Altadena is unincorporated, so there is no city building department; planning review and building permits run through the county. ADU Concepts manages county submittals, corrections, and inspections as part of every Altadena project.
Can I build an ADU while rebuilding my house after the Eaton fire?
Yes, and in many cases you can occupy it first. Under AB 462, effective October 2025, a local agency can issue the ADU's certificate of occupancy before the fire-damaged main home on the same lot receives its own. That lets a family live on their property during the rebuild instead of renting elsewhere. We can design the ADU and the rebuild sequence together.
How much does an ADU cost in Altadena?
The same ranges as the rest of Southern California apply: construction alone starts from about $172,000 for a compact studio, and most one or two bedroom backyard ADUs land in roughly the $290,000 to $410,000 range including design, engineering, and permitting. County fees and your site conditions are budgeted separately. See our California ADU cost guide for starting prices on every layout we build.
How many ADUs can I add to an Altadena lot?
On a single-family lot, state law lets you add up to three accessory units as of right: one ADU converted from existing space, one Junior ADU inside the main house, and one new detached ADU of up to 800 square feet. A single detached ADU can go up to 1,200 square feet under the statewide default that applies in unincorporated LA County.
Is a steel-framed ADU better in a fire area like Altadena?
Light-gauge steel framing is non-combustible: the frame itself does not ignite or feed a fire the way wood framing can. The ADU we built on Palm Street in Altadena survived the Eaton fire that destroyed the main residence on the same property. No construction method makes a building fireproof, and defensible space, vents, roofing, and openings all matter, but a non-combustible frame is a meaningful head start. Steel is our included standard, not an upcharge.
Have you actually built in Altadena?
Yes. We designed and built a 1,200 square foot ADU on Palm Street about four years before the Eaton fire, and it survived the fire. We also have an active single-family project on West Las Flores Drive. You can see our completed projects across Los Angeles County on our projects map.
Talk to a contractor who has built in Altadena
Tell us about your lot, whether it's a fire rebuild, a backyard ADU, or both. We'll walk you through what the county allows and give you a straight, itemized number.
Explore next: ADU cost guide, California ADU laws, or our projects map.