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

Fast, Reliable Home Additions & ADU Across Antioch

Adding square footage or building an ADU in Antioch is not a simple bolt-on job. The city’s split housing stock, its delta clay soils, and its particular permitting history mean a contractor working in Pittsburg or Brentwood all week can still walk into an Antioch project and misread the foundation. A home addition in Antioch typically runs $45,000 to $130,000, and a detached ADU usually lands between $90,000 and $220,000. If you’re weighing whether to add on or build an accessory unit on your property in 94509 or 94531, call Barrett & Sons at (877) 610-1318 for a free estimate. Tom Barrett’s crew works in Antioch weekly, and Tom answers his own phone.

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

Barrett & Sons has been building additions and ADUs in Contra Costa County since 1998. Tom Barrett founded the company and his sons run the crews, which means the name on the truck is the same name you’ll see walking your property line. We are not a franchise dispatching strangers from an out-of-state call center. When you call, a live person picks up. When you have a question about a change order, Tom reads it with you.

We have built additions and accessory units in both halves of Antioch: the older wood-frame homes near Lone Tree Way’s west end and the 2000s-era stucco tracts east of Hillcrest Avenue. That matters because the permitting questions, the foundation checks, and the material choices are different in each pocket of town. Our Antioch customers have told us the biggest reason they call Barrett & Sons is that our price changes always arrive in writing before work begins. The allowance that isn’t on paper is a surprise waiting for a date, and surprise invoices are exactly what burned them with the last company.

Every Antioch job we take includes permits pulled and inspections signed. We do not tell customers permits are optional. The permit inspector works for you, not for us, and we like it that way.

Our Home Additions & ADU Services in Antioch

If you are searching for Home Additions & ADU work, here are the four things Antioch homeowners ask us about most, along with what each looks like on the ground in this city.

ADU Design & Permitting

Antioch’s planning department handles ADU applications regularly, but that does not mean the path is identical from one lot to the next. In western 94509, many lots from the 1950s and 1960s have older septic laterals and electrical panels that need upgrades before an ADU permit will clear. In eastern 94531, the HOA-governed subdivisions sometimes carry design-review requirements on top of city permitting. We handle the drawings, the applications, and the inspections, and we tell you up front what the city will actually require.

Garage Conversion ADU

Converting an attached garage is often the most practical ADU path in Antioch because the square footage already exists under roof. A garage conversion in Antioch typically runs $30,000 to $80,000. In the 2000s-era tract homes east of Hillcrest, we frequently find that the garage slab was poured as a separate pour from the house slab, which means we check for differential settlement before framing any interior walls.

New Detached ADU

A new detached ADU on an Antioch lot usually runs $90,000 to $220,000 depending on square footage, utilities, and whether the unit has a full kitchen. On the clay-heavy ground common across the city, we pay close attention to the foundation specification and drainage. Water management around a new detached unit in Antioch matters more than it would on a hill with fast-draining soil.

Junior ADU & Interior Conversion

A junior ADU built inside the existing footprint of your house can often be done without the full site-prep and utility equipment needed for a detached unit. In many western Antioch homes, the most natural JADU is a converted den, bonus room, or attached garage bay with its own entrance. We size the project around your existing floor plan and bring the permit package to the city exactly the way inspectors expect to see it.

Trusted Brands We Service in Antioch

When we build a paver path or a hardscape connection around a new addition in Antioch, we use Techo-Bloc and Cambridge Pavers products. These are brands you can look up, not mystery materials off a van. For concrete work tied to foundations and slab repairs, we rely on Quikrete products specified for the shrink-swell clay conditions common here. We do not push off-brand alternates to pad a margin, and every material allowance is written into your contract before the first nail moves.

Common Home Additions & ADU Problems We See in Antioch Homes

Antioch produces the same call patterns again and again. Here are the four we see most often on additions and ADU jobs.

• Slab movement on 2000s-era east side tracts. The adobe and expansive clay soils across eastern 94531 swell in winter rains and shrink in the delta heat. We routinely find measurable differential settlement on slabs less than 20 years old, which changes how we spec the addition’s foundation.
• Deferred maintenance from the foreclosure years. Antioch absorbed one of the heaviest foreclosure waves in California after 2008. Many homes went years with little upkeep, and additions often start by correcting rotted fascia, undersized electrical panels, or failing water heaters before new square footage can be framed.
• Permit surprises from previous flips. We find far too many Antioch homes where a previous owner finished a garage or added a room without pulling permits. When you try to add on later, the city wants the old unpermitted work addressed first. We help you sort that out honestly.
• Stucco cracking at corners and window heads. On east Antioch tract homes especially, stair-step stucco cracks at outside corners show up as the soil moves under the slab. We check the perimeter before any addition is designed, because bolting new framing to a shifting foundation just transfers the problem.

Pricing for Home Additions & ADU in Antioch, CA

We Also Serve Cities Near Antioch

Besides Antioch itself, our crews work regularly in Oakley, Brentwood, Bay Point, and Pittsburg. If you live just outside city limits and want the same written-change-order approach, call us. We also handle Kitchen Remodeling in Antioch and Bathroom Remodeling in Antioch when your addition project grows to include those rooms.

FAQs - Home Additions & ADU in Antioch