Home Additions in Contra Costa County. Built Right, Permitted, Done.
DevCo Building Enterprises builds permitted home additions across Contra Costa County, including room additions, second-story additions, garage conversions, and custom expansions. Most home addition projects cost between $120,000 and $350,000 depending on size and scope, and take 6 to 10 months from permit to completion.
Your home is your biggest investment, and sometimes it just needs more space. Whether you're adding a bedroom for a growing family, building out a master suite, or going up with a second story, a home addition is one of the highest-return projects you can do in Contra Costa County. DevCo Building Enterprises handles the full scope: design coordination, permits, construction, and final inspection, all under one contract, with one point of contact. That's Devin Grimes, our licensed general contractor, who's been building additions across Concord, Martinez, Walnut Creek, Pleasant Hill, and the surrounding cities from our Pacheco base.
What Type of Home Addition Can You Build in Contra Costa County?
Every homeowner's situation is different. Here are the most common addition types DevCo builds, along with typical costs and what they're best suited for:
Adding a bedroom, home office, or family room to existing footprint
Expanding or adding a primary bedroom with ensuite bath
Not sure which type is right for your property? DevCo offers free on-site consultations. Devin will walk your lot, review your goals, and tell you exactly what's buildable under Contra Costa County zoning rules before you spend a dollar.
How DevCo Manages Your Home Addition, Start to Finish
Most homeowners haven't been through a major addition before. Here's exactly how our process works so you know what to expect at every stage:
Free On-Site Estimate
Devin visits your property, evaluates the site, confirms zoning setbacks and lot coverage rules, and gives you a real cost range. No ballpark guesses.
Design Coordination
We work with your architect or connect you with our design partners to develop permit-ready plans that meet Contra Costa County standards.
Permit Submission
We handle all applications to your city's planning and building departments and manage every round of comments. Concord, Martinez, Walnut Creek, and Pleasant Hill all have different timelines, and we know what each requires.
Construction
Our crew breaks ground once permits are approved. You get a dedicated point of contact throughout, not a rotating cast of project managers.
Inspections
We schedule and attend all required city inspections and resolve any correction notices before final sign-off.
Final Walkthrough
Devin walks the completed addition with you personally. You don't hand us a final check until you're satisfied.
In our experience building additions across Contra Costa County, the permit process is where homeowners get surprised, either by timeline or by city-specific requirements they weren't told about. We've navigated the planning departments in Concord, Martinez, Walnut Creek, and Pleasant Hill dozens of times. We know what they want, and we prepare your plans accordingly the first time.
Why Contra Costa Homeowners Choose DevCo for Their Addition
One Licensed GC From Permit to Walkthrough
Devin Grimes is a licensed general contractor and the owner of DevCo. He doesn't hand your project off after the sale. He's on site, managing the crew, attending inspections, and answering your calls.
No Surprise Change Orders
We give you a fixed-scope estimate after the on-site visit. That means you know your number before we break ground, not discover it when the bill comes. We build what we quote.
We Know Contra Costa County Permitting
Every city in our service area has different rules around setbacks, lot coverage, height limits, and building code requirements. Concord is different from Walnut Creek, which is different from Martinez. We've done the homework so you don't have to.
Serving the Full 15-Mile Radius
DevCo is based in Pacheco and serves all of Contra Costa County within 15 miles, including Concord, Martinez, Walnut Creek, Pleasant Hill, Clayton, Lafayette, Orinda, and Pittsburg.
Home Addition Costs and Timelines in Contra Costa County
Here's what to expect going into a home addition project in 2026:
Room addition (200–400 sq ft)
Master suite (300–500 sq ft)
Second story (full floor)
Garage conversion
Permit timeline
Total project timeline
These are real ranges based on current labor and material costs in Contra Costa County. Your actual number depends on scope, finishes, site conditions, and structural requirements. The only way to get your number is an on-site evaluation, which DevCo provides free of charge.
Frequently Asked Questions
Most home additions in Contra Costa County range from $80,000 to $400,000+ depending on type, size, and finish level. A single room addition typically runs $80,000–$180,000. A full second-story addition can reach $200,000–$400,000 or more. DevCo provides free on-site estimates so you know your actual number before committing.
Yes. All home additions in California, including all cities in Contra Costa County, require a building permit. This includes room additions, second stories, and garage conversions to livable space. DevCo manages the full permit process: plan submission, city comments, and all inspections are included in our standard service.
From permit submission to final walkthrough, most home addition projects take 6 to 10 months. The permit phase alone typically takes 2 to 4 months depending on the city. Concord and Martinez generally move faster than Walnut Creek. DevCo keeps you updated at every stage.
A home addition expands your existing home's footprint, adding square footage that's attached to and part of the primary structure. An ADU (Accessory Dwelling Unit) is a separate, self-contained living unit on your property with its own entrance, kitchen, and bathroom. DevCo builds both and can help you determine which option makes more financial and practical sense for your property.
Yes. Second-story additions are one of the most efficient ways to add square footage in Contra Costa County without expanding your lot footprint. They do require a structural assessment of your existing foundation and first-floor framing. DevCo manages this evaluation as part of the pre-permit design process.
Yes. DevCo Building Enterprises serves all cities within a 15-mile radius of our Pacheco office, including Concord, Martinez, Walnut Creek, Pleasant Hill, Clayton, Lafayette, Orinda, and Pittsburg. We know each city's permitting requirements and planning department.
Ready to Add On? Let's Talk.
If you're a Contra Costa County homeowner who's ready to move forward on an addition, not just thinking about it, DevCo is ready to give you a real estimate and a straight answer. Call us or fill out a quick estimate request and Devin will follow up within one business day.
Serving Concord, Martinez, Walnut Creek, Pleasant Hill, Clayton, Lafayette, Orinda, Pittsburg, and all cities within 15 miles of Pacheco, CA.
About the Builder
Licensed General Contractor | DevCo Building Enterprises | Pacheco, CA
Devin Grimes is the owner and licensed GC behind DevCo Building Enterprises. He has built home additions, ADUs, and handled seismic retrofitting projects across Contra Costa County, leading every project personally from initial site visit to final city inspection.