Fast, Reliable New Detached ADU Across Altadena
A new detached ADU in Altadena typically costs $280,000 to $420,000 all-in for a custom 1-bedroom unit, drawings through final inspection, and the county planning timeline currently runs five to seven months from submittal to permit issuance. Those numbers change fast when the parcel sits in a High Fire Hazard Severity Zone or when the project folds into an Eaton Fire rebuild package. We handle both cases routinely. If you’re weighing a detached ADU on your Altadena lot, call (971) 497-2402 and we’ll give you a written price before any work starts.
Altadena is not Pasadena. That sounds obvious to anyone who lives here, but it matters for permitting in a way most contractors learn the hard way. Our crews work Altadena weekly, from the flats near Woodbury Road up into the foothills above Loma Alta Drive, and we know what the County wants to see before the first inspection is ever scheduled.
Why Ellery ADU Studio Is Altadena’s Preferred New Detached ADU Company
Since 2015, Ellery ADU Studio has designed, permitted, and built more than 900 ADUs under a single design-build contract. Our New Detached ADU team has handled projects across Altadena’s unincorporated county parcels, including post-Eaton Fire rebuilds where the ADU and the primary home are permitted as one coordinated package. That matters here specifically because Altadena has no city hall. ADU permits route through LA County Public Works Building & Safety at the Alhambra office, and the plan check process, fee structure, and inspector relationships are entirely different from what a Pasadena-based contractor encounters three miles south.
Nadia Ellery founded the studio the year California’s ADU permitting landscape shifted, and she built the practice around a simple rule: the permit set is the product, not an afterthought. Every Altadena client gets written drawings, a written scope, a written price, and a written warranty. The 365-Day Done Right Promise, spelled out in your contract before construction begins, says if the finished ADU isn’t built to the permitted drawings, we make it right. In writing.
Our New Detached ADU Services in Altadena
Custom Built ADU
Custom built detached ADUs in Altadena run $300,000 to $480,000 depending on square footage, site conditions, and fire-zone requirements. We design and build studio, 1-bed, and 2-bed units, and we draft every permit set to LA County standards, including Chapter 7A ignition-resistant detailing when your parcel sits in the High or Very High Fire Hazard Severity Zone above Lake Avenue. You get a single contract covering design, engineering, Title 24, permit submittal, construction, and final inspection.
Prefab ADU Installation
For Altadena lots with tight access or owners who want a shorter on-site build window, we specify and coordinate prefab systems from Cover, Dvele, and Mighty Buildings. A prefab 1-bedroom detached ADU in Altadena typically runs $220,000 to $320,000 including foundation, site prep, utility connections, and county final sign-off. The prefab panelized or modular shell arrives ready for assembly, and we handle every county correction letter, every inspection, and every warranty claim under the same single contract.
Modular ADU
Modular detached ADUs work well on Altadena’s larger lots, especially the 8,000 to 12,000 square foot parcels common in the President Streets and Country Club areas. Because modular units are built off-site in a controlled factory, they compress the county inspection timeline meaningfully, which matters when you’re coordinating an ADU with a fire-rebuild primary home. Budget $240,000 to $340,000 for a modular 1-bed ADU, utility connections included.
Studio ADU
A studio detached ADU in Altadena, roughly 400 to 500 square feet, runs $200,000 to $280,000. These are the most common first-phase units we build for owners who want rental income while the primary home rebuild continues on the same parcel. The studio floor plan keeps the kitchen, bath, and living space efficient, which helps keep the county fees, materials, and construction time under control.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in Altadena
We specify and coordinate prefab and modular systems from Cover, Dvele, Mighty Buildings, and Boxabl, plus fiber cement siding from James Hardie when fire-zone Chapter 7A requirements apply. For Altadena customers, that means we don’t hand you a parts list and walk away. We handle the manufacturer coordination, the county plan check submittal, and the on-site assembly under one written contract. If a panel arrives damaged or a module is out of tolerance, that’s our schedule problem, not yours.
Common New Detached ADU Problems We See in Altadena Homes
- Stop-work orders for non-ember-resistant vents. A builder-grade ADU installed under a standard county plan check without accounting for High Fire Hazard Severity Zone requirements gets flagged because the crawlspace or attic vents aren’t ember-resistant. The correction requires swapping materials after rough-in, which costs time and money that a proper plan check would have caught.
- HOA removal notices in newer enclaves. Owners in Altadena’s newer master-planned developments assume HOA approval is optional and start construction without the required architectural review, triggering a removal notice from the development’s management. The county permit is separate from HOA approval, and both are mandatory.
- Contractors routing to Pasadena’s permit counter. Contractors who only know Pasadena’s city permit desk route to the wrong office, causing weeks of delay and triggering a second plan check fee they didn’t budget for. Altadena permits go through the Alhambra Building & Safety office.
- Setback variance surprises on older lots. Altadena’s 1920s through 1960s housing stock often has odd lot shapes or existing structures that push the new ADU closer to the property line than the county’s standard setback allows. We identify the variance, file it correctly the first time, and avoid the correction letter cycle.
Pricing for New Detached ADU in Altadena, CA
A new detached ADU in Altadena, CA, realistically runs $200,000 to $480,000 depending on size, site access, fire-zone requirements, and whether the project is standalone or bundled into an Eaton Fire rebuild. A studio unit starts near the bottom of that range. A custom 2-bed with Chapter 7A materials, a new utility trench, and slope work runs toward the top. Every quote we give in Altadena is a written price before any work starts, per Haven Standard Clause 1. No door-side upsells, no change orders you didn’t approve in writing. Call (971) 497-2402 to schedule your free written estimate.
| ADU Type | Typical All-In Range, Altadena |
|---|---|
| Studio (400-500 sq ft) | $200,000 - $280,000 |
| Prefab 1-Bed | $220,000 - $320,000 |
| Modular 1-Bed | $240,000 - $340,000 |
| Custom 1-Bed | $280,000 - $380,000 |
| Custom 2-Bed | $350,000 - $480,000 |
We Also Serve Cities Near Altadena
While this page focuses on New Detached ADU in Altadena, our crews also serve Pasadena, South Pasadena, San Gabriel, and Alhambra. Each jurisdiction has its own plan check office and inspector assignments, so we handle each city’s permitting separately. If your property sits in a neighboring city, call and we’ll tell you which office your submittal goes to.
Serving Altadena, CA - Our Local Coverage Area
We’re based in the Altadena area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs - New Detached ADU in Altadena
A new detached ADU in Altadena typically takes five to seven months from plan check submittal to permit issuance through the Alhambra Building & Safety office, which is roughly one to two months longer than a comparable Pasadena city submittal due to county correction-letter cycles and inspector district scheduling. We quote realistic timelines at the start so you don’t lose a tenant season to an office you didn’t know existed. Call (971) 497-2402 for a written estimate and a timeline specific to your parcel.
Only if your parcel is mapped in the High or Very High Fire Hazard Severity Zone, which covers much of Altadena above Lake Avenue up toward the San Gabriel Mountain foothills but does not blanket the flatter neighborhoods below Woodbury Road. We check your parcel’s fire-zone designation during the feasibility phase and tell you in writing whether Chapter 7A materials are required before you spend a dollar on plans.
Yes, and this is the dominant project type we’re seeing across central and eastern Altadena right now. The county’s expedited fire-rebuild pathway allows an ADU-integrated primary-home reconstruction package to go through as one coordinated submittal, which saves plan check time and often reduces total permit fees compared to two separate filings. We handle the combined drawings and shepherded the package through the Alhambra office.
Yes. The LA County permit covers building code and zoning, but an HOA’s architectural review is a separate private approval, and building without it can trigger a removal notice even after the county signs off. We prepare the architectural package your HOA requires, and we don’t start construction until both approvals are in writing.
The first upgrade worth making is the exterior cladding, because under Chapter 7A rules in the foothill fire zones, builder-grade siding often doesn’t meet ignition-resistant standards and switching to James Hardie fiber cement early avoids a tear-off later. Leave the interior finishes at standard level if this is a rental unit; spending $15,000 on upgraded cabinets won’t move the rent in Altadena, but it will move your cash. Call (971) 497-2402 for a written price on your specific scope.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Altadena since 2015.