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

Fast, Reliable Home Additions & ADU Across Downey

Home additions and ADU construction in Downey typically run $45,000 to $130,000 for a room addition, and $90,000 to $220,000 for a new detached ADU. Most projects take four to ten months from permit submission to final inspection, depending on whether you’re converting a garage or building from scratch. Our Home Additions & ADU team knows Downey’s post-war housing stock, the Building & Safety Division’s review quirks, and what it takes to keep a growing family in the home they already love. Call (877) 610-1318 for a free estimate, and we’ll walk the property with you before you sign anything.

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

We’re not a franchise that sends a different crew every week. Barrett & Sons is owner-operated and has been since 1998. Tom Barrett and his sons run the crews themselves, and they’re on-site most days. That means the person you shake hands with at the estimate is the same person you’ll see framing your addition. For Downey homeowners, that predictability matters. A lot of you have told us you’ve been burned before, quoted one price over the phone and handed a different bill at the door. We put every scope, every allowance, and every price change in writing as a change order before work proceeds. No surprises waiting at the end.

We also understand the city’s review process. Downey has its own Building & Safety Division, and pulling a structural permit here often triggers a conversation about seismic requirements on older homes. We handle that conversation so you don’t have to. Our crews are background-checked and uniformed, and a live person answers our phone around the clock. Look up Tom Barrett’s name, address, and license number before you sign anything with us or anyone else. We publish it because we stand behind it.

Our Home Additions & ADU Services in Downey

ADU Design & Permitting

State law made ADUs easier to permit, but Downey still has its own zoning and setback rules. We handle the design, the plot plan, the energy calculations, and the permit submittal. If your house sits east of Lakewood Blvd on a raised foundation from the 1950s, expect the city to ask about cripple-wall bracing and foundation bolting before approving structural work. We plan for that from day one, so your permit doesn’t stall in review. A typical design-and-permitting package in Downey runs $8,000 to $20,000 depending on the complexity of the site and the level of drawings required.

Garage Conversion ADU

Downey has thousands of detached garages built in the 1950s and 1960s, many of them underused. Converting one into an ADU usually costs between $30,000 and $80,000, and it’s often the fastest path to a rentable unit because the shell is already there. The catches are the usual ones: the slab may not meet current insulation requirements, the original electrical feeder is probably undersized, and the roof structure might need reinforcement. We address all of it in writing before we start, and we pull the permit so the inspector signs off on the finished unit.

New Detached ADU

Building a new detached ADU in Downey runs $90,000 to $220,000, depending on size, finish level, and site conditions. The flat, low-lying parcels near the Rio Hondo channel corridor can have drainage issues that need grading and foundation waterproofing before we pour concrete. We also coordinate the new electrical service, the sewer lateral connection, and the fire-rated separation from the main house. If you want an ADU for an aging parent or a grown child, this is the option that gives everyone their own front door without leaving the neighborhood.

Junior ADU & Interior Conversion

A Junior ADU is a smaller, attached unit created from existing interior space, like a spare bedroom suite with its own entrance and a small kitchenette. These run $45,000 to $90,000 in Downey and are a smart fit for the city’s 1,100 to 1,600 square foot ranch homes where a full addition isn’t feasible on the lot. Interior conversions also let us keep the original roofline and exterior walls intact, which matters when you’re working with a post-war home where every wall we move is one the city wants engineered. We bring in a structural engineer when the layout calls for it, and the engineer’s drawings go to the city with your permit application.

Trusted Brands We Service in Downey

We install materials you can look up. For windows in Downey additions and ADUs, we regularly use Simonton and Ply Gem. Both hold up to the inland heat better than cheap imports, and we can tell you exactly what you’re getting before we order anything. For impact-rated openings near the Rio Hondo corridor, we’ve used PGT as well. We don’t sell mystery brands off a van. Whatever we quote, you can check the manufacturer, the model number, and the warranty on your own time. That’s the way pricing should work.

Common Home Additions & ADU Problems We See in Downey Homes

• Cripple-wall foundations that were never bolted to the mudsill. East of Lakewood Blvd especially, we regularly open up houses where the 1950s raised foundation has no seismic tie-down at all. Downey Building & Safety flags this on nearly any addition that pulls a structural permit, so we plan for the retrofit as part of the project rather than letting it become a surprise.
• Undersized 100-amp electrical panels. Most of the post-war ranch homes in Downey still run on 100 amps, which wasn’t a problem when the house had a window AC unit and a few lamps. Add a second kitchenette or a mini-split system for an ADU, and you’re over budgeted load. We typically upgrade the panel as part of the ADU scope and write that cost into the estimate from the beginning.
• Aging galvanized or cast-iron drain lines. Homes built between 1948 and 1968 often have original drain plumbing that’s corroded inside. When we tie a new bathroom or kitchenette into the system, we camera the lines first. If they’re near failure, we tell you in writing and give you a separate price before we touch anything.
• Single-pane aluminum windows that leak heat. Downey runs noticeably hotter than the coastal cities in summer and during Santa Ana events. Old single-pane windows make a new addition uncomfortable before it’s even finished. We quote replacement windows as part of the addition scope when it makes sense, so the new space actually performs.

Pricing for Home Additions & ADU in Downey, CA

We Also Serve Cities Near Downey

Our crews work throughout the surrounding area, including Bell Gardens, Santa Fe Springs, Paramount, and Pico Rivera. If you live in Home Additions & ADU in Downey or any of the neighboring communities, the same owner-operated crew handles your project from estimate to final inspection. And if you’re thinking about other work while we’re on-site, we also handle Kitchen Remodeling in Downey and Bathroom Remodeling in Downey.

FAQs - Home Additions & ADU in Downey