ADU builder · Altadena, CA
ADU builder in Altadena.
Design, permits, financing and construction from one local team. 600+ ADUs delivered across greater LA, including projects in and around Altadena.
Licensed & insured · Construction from $275/sq ft · 5.0★ rated
Building an ADU in Altadena
The Eaton Fire in January 2025 destroyed thousands of homes and buildings in Altadena, and a lot of the ADU work here now is part of rebuilding. Some families want a smaller unit to live in while the main house goes back up. Others are adding a second home for parents or a rental, and owners of multifamily lots ask whether they can add more than one ADU. ADU permits in Altadena jumped to roughly 270 in 2025, up from about 60 to 80 in each of the two years before, based on our count of state housing report data for unincorporated LA County.
ADU Resource Center designs, permits and builds ADUs with one in-house team. In Altadena we built a two-story stucco ADU with a wide sliding door that opens onto a new concrete patio, set against the property's old stacked-stone retaining wall. Our other nearby work is in Pasadena and Sierra Madre, including a 3-bedroom cottage ADU and a detached 2-bedroom unit that went up where a failing garage stood.
You'll see the full construction price in a fixed quote before work starts, and one project manager stays with you from design to final inspection. We can also help you line up financing, which matters when insurance money and a rebuild budget have to stretch across two buildings.
ADUs in Altadena: quick facts
Updated November 2026
- Who issues ADU permits
- Los Angeles County: Public Works Building and Safety, with Regional Planning
- Our construction rates
- $275, $300 or $325 per sq ft (basic, mid-range, luxury); garage conversions $235–$285 per sq ft
- Example cost
- A 600 sq ft one-bedroom runs about $165K–$195K in construction
- Size limits under state law
- Detached ADUs up to 1,200 sq ft on many lots; junior ADUs up to 500 sq ft inside the home
- Permit decision
- State law requires a decision within 60 days of a complete application
- Who builds it
- ADU Resource Center: design, permits and construction by one team, 600+ ADUs delivered, office in Glendale
ADU rules change. We confirm the current rules for your lot on the free consultation.
Real projects in and around Altadena
Our work in and around Altadena.
Hear it from our clients
Homeowners on building their ADU with us
More stories on our testimonials page.
Local know-how
What to know before building in Altadena.
LA County is your permit office
Altadena has no city government, so ADU permits come from LA County Public Works Building and Safety, with zoning review by Regional Planning. Fire-affected owners can use the county's Altadena One-Stop Permit Center. We submit the plans and handle the corrections.
Rebuild rules keep changing
Since the Eaton Fire the county has added rebuild options such as like-for-like rebuilds and pre-approved plans, and those programs keep getting revised. Check LA County's recovery site and bring your questions to the consultation.
Fire hazard maps grew in 2025
CAL FIRE's 2025 update expanded the very high fire hazard severity zone in Altadena beyond the old ring along the foothills. Lots in that zone need ignition-resistant roofing, vents and siding, and we design to it from the first drawing.
Slopes and older site walls
Lots closer to the mountains often slope, and many have old retaining walls like the one beside our Altadena project. Grading and new walls add cost, so we look at them early. Our cost calculator gives a quick starting number for the building itself.
What it costs
ADU cost in Altadena
We build at a flat rate per square foot: $275 (basic), $300 (mid-range) and $325 (luxury) finishes. Here's what that means for common sizes. Construction only; design, permits and city fees are quoted separately on your consultation.
| ADU size | Basic | Mid-range | Luxury |
|---|---|---|---|
| 400 sq ft studio | ~$110K | ~$120K | ~$130K |
| 600 sq ft 1-bedroom | ~$165K | ~$180K | ~$195K |
| 800 sq ft 2-bedroom | ~$220K | ~$240K | ~$260K |
| 1,000 sq ft 2–3 bedroom | ~$275K | ~$300K | ~$325K |
Get a number for your exact size: ADU cost calculator · Browse ADU floor plans · Converting a garage? See garage conversion cost.
Free consultation
Start your Altadena ADU.
Tell us about your property. We'll confirm what's buildable, give you a real price range and walk through financing within 1 business day.
Questions
Altadena ADU questions, answered.
Still have a question? Ask us during your free consultation.
Who issues ADU permits in Altadena?
Altadena is unincorporated, so there is no city hall to apply to. ADU plans go to LA County: Public Works Building and Safety handles the building permit, and Regional Planning reviews zoning. For Eaton Fire properties, the county runs a one-stop permit center in Altadena. We prepare the plans, submit them to the county and answer the plan-check corrections.
Can I build an ADU while I rebuild after the Eaton Fire?
Many owners are looking at it, and county filings show rebuild projects that pair a replacement house with a new detached ADU. The county's rebuild rules and fee programs have changed several times since January 2025, so check LA County's recovery site (recovery.lacounty.gov) for the current options. On a consultation we look at your lot and tell you what we'd plan around today.
Can I build more than one ADU on a multifamily lot in Altadena?
Often, yes. State law lets many multifamily lots add more than one ADU. Whether yours qualifies depends on its zoning, size and access, which we confirm before design. Multi-family ADU projects are quoted individually.
How much does an ADU cost in Altadena?
Our construction rate is a flat $275, $300 or $325 per sq ft for basic, mid-range or luxury finishes, so a 600 sq ft one-bedroom comes to roughly $165K–$195K. Garage conversions run $235–$285 per sq ft. Sloped foothill lots, fire-resistant materials and utility work can move the fixed quote, and we price those before you sign.
Does fire zone status change how an Altadena ADU is built?
If your parcel is mapped as a very high fire hazard severity zone, the ADU needs ignition-resistant construction such as rated roofing, ember-resistant vents and noncombustible siding. CAL FIRE updated its maps in 2025 and the very high zone grew in Altadena, so we check the current map for your address before the first drawing.
Free consultation
Ready to build your ADU in Altadena?
Tell us about your property and we'll confirm what's buildable, give you a real price range and lay out financing on one free call.
