Home Additions in Contra Costa County - Room Additions, Second Stories & More
DevCo Building Enterprises builds fully permitted home additions across Contra Costa County - room additions, master suite additions, second story additions, and full home expansions in Concord, Walnut Creek, Martinez, Lafayette, and Orinda. Home addition costs range from $200 to $400 per square foot, with most projects totaling $80,000 to $400,000. Owner Devin Grimes leads every project from permit to final walkthrough. Call (925) 448-2123.
When your family grows, your needs change, or you simply want more space without the disruption and cost of moving in Contra Costa's competitive real estate market, a home addition is often the most practical and financially sound decision. Adding a master bedroom suite, expanding a kitchen and family room, or building a complete second story can add 60 to 80 percent of construction cost back to your home's value according to Remodeling Magazine's 2025 Cost vs. Value report.
Types of Home Additions DevCo Builds in Contra Costa County
Home Addition Permits in Contra Costa County: What to Expect
Every home addition that adds square footage to a permitted structure requires a building permit from the relevant city or county building department. In Contra Costa County, this means submitting architectural and structural plans, going through plan check (typically 6 to 12 weeks), and passing all required inspections during construction.
In our experience managing addition projects across Concord, Walnut Creek, and Martinez, two issues slow projects down most often:
Incomplete plan sets that trigger plan check corrections
Underestimating setback and FAR constraints on the parcel
DevCo reviews your parcel constraints before design begins and submits complete plan packages to minimize corrections and delays. We manage all permit communication on your behalf.
Frequently Asked Questions - Home Additions Contra Costa
$200 to $400 per square foot depending on scope and finishes. A 400 sq ft master suite runs $100,000 to $150,000. A full second story addition runs $250,000 to $400,000+. DevCo provides free estimates.
Yes. All additions that add square footage require a building permit. DevCo manages the full permit process including plan preparation, submission, and inspection coordination.
Single room additions take 3 to 6 months. Second story additions take 5 to 9 months. Permitting typically adds 6 to 12 weeks.
Yes. According to Remodeling Magazine's 2025 Cost vs. Value Report, major home additions in the San Francisco Bay Area recover 60 to 80 percent of construction cost in resale value on average. Adding a master suite or second story in Walnut Creek or Concord can meaningfully increase your home's market value.
An addition expands your existing home's footprint but remains part of the main house. An ADU is a fully self-contained separate living unit with its own entrance, kitchen, and bathroom. DevCo builds both. ADUs are better for rental income; additions are better for household living space expansion.
Get a Free Home Addition Estimate
Serving Concord, Walnut Creek, Martinez, Lafayette, Orinda, Pleasant Hill, Clayton, and surrounding Contra Costa County communities.
Call (925) 448-2123 or visit devco.llc/contact.