Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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AfterFast, Reliable Home Additions & ADU Across Altadena
Building a room addition or ADU in Altadena means working through LA County, not a city hall, and that changes everything about your permit, your timeline, and your budget. A typical Home Additions & ADU project here runs $45,000-$130,000, while a new detached ADU lands between $90,000 and $220,000 depending on foundation conditions, fire code requirements, and utility runs. We’ve built in every corner of Altadena since we started taking this work seriously after the Eaton Fire, and we know exactly which county desk to call and which inspection will trip you up. Call (877) 610-1318 and we’ll walk your lot with you before you spend a dollar on plans.
Why Barrett & Sons Construction Is Altadena’s Preferred Home Additions & ADU Company
Tom Barrett founded this company in 1998, and his sons run the crews that show up on Altadena jobsites. That’s not a pitch, it’s just how we work. When you call, a live person answers, and the person who walks your property is someone whose name is on the truck.
Altadena homeowners have been through enough. Many of you are rebuilding after the Eaton Fire, and the last thing you need is a contractor from across town who doesn’t know that Altadena permits don’t go through Pasadena, that soil testing is a county requirement on burned lots, and that your inspector is looking for Class A roofing and ember-resistant vents whether you like it or not. We know all of that because we’ve filed those permits, passed those inspections, and re-graded those slopes.
Every scope we give you is in writing. Every change order is in writing. Every allowance is in writing. And every job carries our 90-Day Done Right Promise, written on the contract. If it’s not right, one call brings Tom back.
We publish our name, our address, and our license number. Look us up before you sign anything. Then ask anyone on your street.
Our Home Additions & ADU Services in Altadena
ADU Design & Permitting
Altadena ADUs are permitted through LA County’s Department of Public Works, not a municipal building department. That means your plans have to clear county plan check, county fire review, and the Very High Fire Hazard Severity Zone requirements that don’t apply across the border in Pasadena. We prepare drawings that anticipate every county objection before you pay for a single review cycle, and we pull every permit ourselves. No permit, no work.
New Detached ADU
A detached ADU on an Altadena lot usually means working around an existing septic system, dealing with alluvial-fan soils, and meeting WUI fire codes that dictate everything from your roof assembly to your vent screens. We’ve built 800 to 1,200 square foot detached units on lots in the Meadows, near Farnsworth Park, and up against the mountain front. The $90,000 to $220,000 range reflects real conditions on the ground here, not a brochure number.
Garage Conversion ADU
Converting an existing garage is the most cost-effective ADU path in Altadena, typically $30,000 to $80,000. But many pre-fire garages in the 91001 and 91003 zip codes are wood-framed structures that won’t pass fire inspection without significant upgrades. We handle the structural evaluation, fire-rated assembly requirements, and utility separation so your conversion doesn’t stall at final inspection.
Junior ADU & Interior Conversion
A JADU converts existing interior space into a small, attached unit, which keeps you out of the most expensive foundation and fire-code territory. In Altadena, JADUs still route through LA County review, and we see a lot of 1940s and 1950s homes where the electrical panel and water lines need upgrading before the conversion can be signed off. We scope all of that in writing before we quote you.
What happens when you call
- 1
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 don’t install materials we wouldn’t put on Tom’s own house. For Altadena ADUs and additions, we regularly work with Techo-Bloc and Cambridge Pavers for hardscape and patio connections, and Quikrete products for the foundation work that matters most in this soil. We carry these brands because they hold up to Altadena’s sun, wind, and fire-season conditions, and because you can look them up yourself. No mystery brands off a van.
Common Home Additions & ADU Problems We See in Altadena Homes
- Burned-out slabs and contaminated soil. The Eaton Fire left ash and burned building material that leaches heavy metals and VOCs into the ground. Skipping LA County’s soil contamination testing stalls your foundation permit and can force a costly re-excavation after you’ve already paid for grading.
- Septic setbacks that kill the ADU placement. Many Altadena lots in 91001 and 91003 sit on aging septic systems, and a detached ADU has to respect the drain field and required setbacks. Design one over or too close to that field without a geotechnical survey and the county sends your plans back.
- Wood framing and asphalt shingles that fail fire inspection. The VHFHSZ Wildland-Urban Interface code doesn’t care what your original house was built with. New construction and major additions need fire-resistant assemblies, Class A roofing, and ember-resistant vents. We’ve seen additions torn apart by inspectors over standard materials that would have passed in Pasadena.
- Older foundations under second-story loads. Altadena’s pre-fire housing stock was largely 1920s to 1950s wood-frame construction. A second-story addition on a 1950s ranch requires a structural engineer to verify the existing footings and slab before you ever order lumber. We get that answer in writing before we quote, so you’re not guessing.
Pricing for Home Additions & ADU in Altadena, CA
Here’s what honest numbers look like for this market:
| Project | Typical Altadena Range |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
What moves the number in Altadena more than anything is what’s under your feet and what the county makes you do before you build. A lot that needs soil remediation, retaining wall replacement, or a full geotechnical re-evaluation will push you toward the higher end. A clean lot with an existing foundation that can take an addition, and a simple utility tie-in, lands you lower. We quote with a line-item scope and written allowances, so you see exactly where every dollar sits. Call (877) 610-1318 for a free estimate. No trip charge inside the county.
We Also Serve Cities Near Altadena
We work throughout Altadena and across the nearby communities: Pasadena, La Cañada Flintridge, East Pasadena, and San Marino. Each has its own permit office and quirks, but the same crews, the same written change orders, and the same 90-Day Done Right Promise follow the work.
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 - Home Additions & ADU in Altadena
Altadena ADU permits go through LA County’s Department of Public Works, not through the City of Pasadena and not through any Altadena city hall, because Altadena is an unincorporated community. That single fact changes your plan check process, your inspection schedule, and your timeline. We file with the county, track every review, and schedule inspections so you’re not waiting on a desk you don’t know exists. Call (877) 610-1318 and we’ll explain the county path for your specific lot.
The VHFHSZ Wildland-Urban Interface code requires your attached addition to use fire-resistant exterior assemblies, Class A roofing, and ember-resistant vents, even if the original house predates all of those requirements. That means standard wood framing and asphalt shingles can fail inspection and force a tear-off. We design for the code from the first drawing, so your addition passes on the first pass. Call (877) 610-1318 for a free estimate on a code-compliant addition.
No, and you shouldn’t try. A detached ADU has to respect the drain field and required setbacks under LA County rules, and building over it will get your plans rejected and can compromise the system that already handles your waste. We bring in a survey and geotechnical review before we place the ADU footprint, then design the unit around what your lot can actually do. Call (877) 610-1318 and we’ll tell you what your lot will hold.
Burned lots in Altadena require soil contamination testing for heavy metals and VOCs before the county will approve any foundation permit, and many also need retaining wall and grading re-evaluation because fire suppression water shifted alluvial-fan soils. We handle the testing, the remediation if it’s needed, and the geotechnical report as part of our written scope, so you’re not surprised by a re-excavation halfway through the job. Call (877) 610-1318 to get your lot evaluated before you spend money on plans.
A second-story addition on a 1920s to 1950s Altadena home requires a structural engineer to verify the existing footings, foundation condition, and load path before you order a single board. Some older foundations can take the load with minor upgrades. Others can’t. We get the engineering answer in writing, include it in your quote, and never build a second story on a guess. Call (877) 610-1318 for a free estimate that includes the engineering review.
If you’re ready to talk about an addition or ADU on your Altadena lot, call (877) 610-1318. We’ll walk the property with you, explain exactly what LA County is going to require, and hand you a written scope with real numbers. No surprises, no phone quotes that morph into bigger bills, no permits skipped. Just a contractor who lives twenty minutes away and answers his own phone.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Altadena and the surrounding communities since 1998.