ADU Construction in Contra Costa County - Licensed. Local. Done Right.
DevCo Building Enterprises builds fully permitted ADUs across Contra Costa and Alameda Counties, including Concord, Walnut Creek, Martinez, Lafayette, and Orinda. Most projects range from $150,000 to $350,000 and take 6 to 12 months from permit to final walkthrough. Owner Devin Grimes leads every project - one licensed contractor, one point of contact, no hand-offs. Call (925) 448-2123 for a free estimate.
Building an ADU on your Contra Costa property is one of the smartest investments a homeowner can make in 2026. With California's ADU laws now requiring cities to approve most applications within 60 days, and the CalHFA grant program offering up to $40,000 to eligible homeowners, the window to add rental income, house family, or increase property value has never been more accessible. DevCo Building Enterprises, based in Pacheco, has been doing exactly this for Contra Costa homeowners - handling everything from initial site assessment through permit, construction, and final walkthrough.
What Types of ADUs Does DevCo Build?
Every Contra Costa property is different, and the right ADU type depends on your lot, existing structures, budget, and goals. DevCo builds all three main ADU categories:
How Much Does an ADU Cost in Contra Costa County?
ADU construction costs in Contra Costa County range from $150,000 to $350,000 for a standard detached unit. Here is what drives cost:
Size: A 400 sq ft studio ADU costs significantly less than a 1,000 sq ft 2-bedroom unit
Site conditions: Sloped lots, poor soil, or utility connection distance increases cost
Finishes: Standard finishes keep costs lower; high-end kitchens and baths push costs up
Existing structure: Garage conversions cost less than ground-up detached builds
City fees: Concord, Walnut Creek, Martinez, and unincorporated areas all have different permit and impact fee structures
According to the California Department of Housing and Community Development, the statewide average ADU construction cost was approximately $200,000 in 2024, with Bay Area costs running 20 to 40 percent above the state average due to labor and material pricing.
DevCo provides free on-site estimates with detailed line-item breakdowns. We do not give ballpark quotes over the phone because every Contra Costa lot is different.
How Long Does It Take to Build an ADU in Contra Costa County?
From your first call to keys in hand, plan for 6 to 12 months on most Contra Costa ADU projects. Here is the typical timeline:
Initial consultation and site assessment:
Week 1 to 2
Design and plan preparation:
4 to 8 weeks
Permit application submission:
varies by city
Plan check and permit approval
6 to 16 weeks (Concord tends to be faster than Walnut Creek)
Construction:
3 to 6 months depending on scope
Final inspections and certificate of occupancy:
2 to 4 weeks
In our experience managing ADU projects across Concord, Walnut Creek, and Martinez, the permitting phase is where most projects lose time. DevCo submits complete, accurate plan sets the first time to avoid plan check corrections that add weeks to the schedule.
The CalHFA ADU Grant: Up to $40,000 for Eligible Contra Costa Homeowners
The California Housing Finance Agency (CalHFA) ADU Grant Program provides up to $40,000 in grant funding to eligible homeowners for ADU predevelopment and construction costs. No repayment is required if the homeowner meets program conditions.
Grant funds cover: site prep, architectural fees, permits, and construction costs
Income limits apply based on Contra Costa County area median income (AMI)
The property must be owner-occupied
Funds are available while the program has budget - apply early
DevCo is familiar with the CalHFA program and works with eligible clients on the documentation required. Visit calhfa.ca.gov/adu for current program details and income limits.
Frequently Asked Questions
Yes. All ADU construction in Contra Costa County requires a building permit regardless of city or unincorporated area. California's ADU laws have simplified the approval process - cities must approve most ADU applications within 60 days of a complete submittal. DevCo handles all permit applications, plan submissions, and city coordination as part of every project contract.
California state law allows detached ADUs up to 1,000 square feet. JADUs (Junior ADUs) are capped at 500 square feet. Some cities in Contra Costa allow larger attached ADUs. Setback requirements (typically 4 feet from rear and side property lines), lot coverage limits, and FAR restrictions vary by city and parcel. DevCo reviews your specific parcel before design begins.
Yes. ADUs can be rented as long-term rentals in Contra Costa County. Most Concord, Walnut Creek, and Martinez ADUs rent for $1,800 to $3,200 per month depending on size, location, and finishes. Short-term rental rules vary by city and HOA - check local ordinances before listing on Airbnb or similar platforms.
California law generally allows one ADU and one JADU on a single-family parcel. Multifamily properties may allow multiple ADUs depending on the number of existing units and local ordinance. DevCo can review your parcel and the applicable rules for your specific address.
DevCo manages the complete ADU process from design through permit to final walkthrough. We work with structural engineers and designers as needed and coordinate all plan submissions. You have one point of contact - the owner - for the entire project.
An ADU (Accessory Dwelling Unit) is a fully independent living space with its own kitchen, bathroom, and entrance - it can be detached from the main house or attached. A JADU (Junior ADU) is a smaller unit (up to 500 sq ft) created within the existing footprint of the primary residence, sharing some systems with the main house. JADUs are faster to permit and lower cost but have size limitations.
Why Contra Costa Homeowners Choose DevCo
Kevin S., a bakery owner who hired DevCo for his first commercial buildout, put it best: 'Your team was incredibly hands-on, not only with the construction but also with project management. I particularly appreciated the precise timelines, daily and weekly updates.'
Antonio W., whose home was damaged by a previous contractor before DevCo came in: 'His crew was amazing. They were very punctual, very hard working and very clean. I would hire them in an instant.'
DevCo is an owner-operated contractor. Devin Grimes is on every project - not a salesperson who hands you off to a crew you have never met. Every project has a dedicated project manager and a clear scope, timeline, and cost before a single nail is driven.
Get a Free ADU Estimate in Contra Costa County
Serving Concord, Walnut Creek, Martinez, Lafayette, Orinda, Pleasant Hill, Clayton, Pacheco, and surrounding Contra Costa and Alameda County communities within a 15-mile radius.
Call (925) 448-2123 or fill out the estimate form at devco.llc/contact. We respond within one business day and typically schedule on-site consultations within 48 to 72 hours.