Home Additions & ADU in Downey - One Fixed Price, Permits Handled

Fast, Reliable Home Additions & ADU Across Downey

A new room addition or detached ADU in Downey typically runs $45,000-$130,000 for an addition and $90,000-$220,000 for a new detached ADU, with most projects spending 3-6 months from permit to final inspection. That’s the honest range before we walk your property. Before you commit to any number, though, you need to understand what Downey’s own Building & Safety Division will require, because in this city those requirements hit harder than almost anywhere else in the LA Basin.

Call (877) 610-1318

Barrett & Sons Construction has been building additions and ADUs since 1998, and we know Downey’s 1950s ranchers, its permit sequencing, and its drainage quirks. Call (877) 610-1318 and we’ll scope your project properly, pull the permit history, and hand you a written price before a single board gets cut. Tom Barrett runs the crews personally, and his sons are on-site most days.

Why Barrett & Sons Construction Is Downey’s Preferred Home Additions & ADU Company

We’re not a franchise dispatching strangers to your door. Tom Barrett founded this company in 1998, and the name on the truck is the name on the contract. When you call (877) 610-1318, a live person answers, not a voicemail box or an out-of-state call center. That matters when you’re five figures into a project and want a straight answer.

More than anything, we understand the houses Downey is built on. The neighborhoods east of Lakewood Blvd, west of the 605, and north of Firestone were thrown up in a hurry between 1948 and 1968 for aerospace workers at the old North American Aviation plant. Those homes, mostly 1,100-1,600 sq ft stucco ranchers on raised cripple-wall foundations, are now hitting 60-75 years old simultaneously. What that means for you: aging galvanized drain lines, undersized 100-amp panels, and foundations that were never bolted to the mudsill. We pull Downey permit history before we quote, so the number we give you is the number it costs. Every change order arrives in writing before work proceeds. That’s not a slogan, it’s how we’ve stayed in business 29 years.

We also publish Tom’s name, address, and license number. Look it up before you sign anything. Ask anyone on your street, or check the L.O.C.A.L. values we operate by: Local roots, On time, Community first, Accountable, Loyal.

Our Home Additions & ADU Services in Downey

Our Home Additions & ADU team handles the full scope, from the first permit drawing to the final inspection sign-off. Here’s what we focus on for Downey homeowners:

ADU Design & Permitting

Jumping into an ADU build without understanding Downey’s permit triggers is the quickest way to blow a budget. On nearly any structural permit here, the city’s reviewers look at your original foundation first. If that 1950s cripple wall was never bolted to the mudsill, expect a mandatory seismic retrofit before your ADU plans get approved. We handle that workflow, not just the floorplan. We draw the plans, submit to Downey Building & Safety, schedule every inspection in sequence, and stand next to you when the inspector walks the site. The permit inspector works for you, not for me, that’s why I like him.

Garage Conversion ADU

Converting a garage into an ADU in Downey doesn’t mean just hanging drywall. The original garage slab is often uninsulated and thinner than current code requires, and the existing electrical panel in a 1950s home is almost always 100 amps, too small to feed a new living unit. Prices for a garage conversion ADU in Downey run $30,000-$80,000, depending on whether we’re cutting new footings, upgrading the panel to 200 amps, or replacing old galvanized supply lines. We scope all of it before quoting, not after you’ve signed.

New Detached ADU

A new detached ADU on a Downey lot gives you a separate address, a separate meter, and real rental value without touching your house. But on flat, low-lying parcels, especially near the Rio Hondo channel corridor, site prep and drainage are the invisible budget items. We test soil before we pour, grade so water moves away from both structures, and size the foundation for the seismic loads Downey will require. A detached ADU here runs $90,000-$220,000, with the spread driven mostly by foundation complexity, utility trenching, and finish level.

Junior ADU & Interior Conversion

A junior ADU, typically 500 sq ft or less carved out of existing square footage, is often the most cost-effective path in Downey because it triggers fewer structural reviews than a detached unit. Think of converting a large dining room or underused family room into a self-contained unit with its own entrance, kitchenette, and bath. It still requires permitting, and it still triggers the same panel and drain evaluation on older homes. But it skips the foundation work entirely, which is where costs climb fastest in this city.

Trusted Brands We Service in Downey

We don’t install mystery materials off a van. On window packages for additions and ADUs in Downey we install Simonton, Ply Gem, and PGT, brands you can look up, with published spec sheets and real warranties. The same rule applies across every trade we touch. If the brand isn’t printed on the box and traceable to a manufacturer’s warranty, it doesn’t go into a Barrett & Sons job. For Downey clients, that means windows rated for inland LA Basin heat and Santa Ana wind-driven rain, not coastal glass specs that underperform where you live.

Common Home Additions & ADU Problems We See in Downey Homes

• Unbolted cripple walls on 1950s raised foundations. East of Lakewood Blvd, the original builders rarely bolted sill plates to the foundation. Downey Building & Safety now flags this on nearly every structural permit, and the retrofit, typically $8,000-$20,000 depending on access and condition, becomes a line item before your addition or ADU can proceed.
• 100-amp electrical panels on post-war homes. Most Downey ranchers built in the 1950s carry 100-amp service, sized for a family with a refrigerator and a few lamps. Add a second unit with a range, laundry, and HVAC and you’re looking at a panel upgrade to 200 amps, usually $3,500-$6,000, before the ADU rough-in inspection will pass.
• Galvanized and cast-iron drain lines reaching end of life. We regularly open walls on Downey additions and find original galvanized supply lines narrowed by 60 years of mineral buildup, or cast-iron drains cracked at the hub. Replacing the affected runs before closing walls saves you a demolition bill later.
• Drainage stress on flat parcels near the Rio Hondo channel. Streets in the 90240 and 90241 zip codes that sit low and flat need real grading attention when you add foundation area. Water that used to sheet across the backyard now hits a new wall. We grade and, where needed, add area drains so your permit passes and your slab stays dry.

Pricing for Home Additions & ADU in Downey, CA

We Also Serve Cities Near Downey

Our crews work throughout the neighboring communities, including Bell Gardens, Santa Fe Springs, Paramount, and Pico Rivera. If you’re just outside the Downey city line, check our Home Additions & ADU in Downey page for scope details, or call us directly. We’ll tell you honestly whether your address falls under Downey’s Building & Safety Division or another authority, and what that changes for your permit.

FAQs - Home Additions & ADU in Downey