ADU Construction projects in Brentwood reflect the realities of the East Bay / Contra Costa County construction market: skilled-labour rates, permit fees, and material costs that sit above the national average. ADU costs in the Bay Area are among the highest in the country, driven by land costs, permit fees, and labor. That said, the rental income potential consistently exceeds the carrying cost of a construction loan — making most Bay Area ADU projects financially sound.
Cost Ranges for ADU Construction in Brentwood
The following ranges reflect current pricing for Brentwood and the wider East Bay / Contra Costa County area:
- JADU (Junior ADU, within existing space): $32,000–$80,000
- Garage conversion (full ADU): $96,000–$176,000
- Attached ADU addition: $128,000–$240,000
- Detached ADU (500–800 sq ft): $144,000–$256,000
- Detached ADU (800–1,200 sq ft): $208,000–$360,000
- ADU design and permits (no construction): $12,000–$32,000
Labour and Market Costs in Brentwood
Licensed tradespeople in the Bay Area — plumbers, electricians, tile setters, carpenters — work in one of the highest labour markets in the country, typically billing $100–$140 per hour.
Key Factors That Affect Your Price
- Unit size — every additional square foot adds cost
- Foundation type — slab vs. crawl space vs. basement
- Utility connections — new meter, sewer lateral, and gas connections
- Finishes — kitchen appliances, flooring, tile quality
- Site conditions — slope, access, tree removal
- Plan check fees — San Francisco charges among the highest in the state
Permit Requirements
Many adu construction scopes in Brentwood require permits through the Brentwood Building Department. Permit fees typically add $500–$3,000 to a project’s total. A licensed contractor should pull all required permits — if a contractor suggests skipping permits on significant work, that is a red flag.
Getting an Accurate Estimate
IronNest Construction does not take on this trade and does not bid it — we are a Class B general builder and we only quote work we carry insurance for. Use the ranges above to judge the quotes you do get: insist on a written, fixed-scope estimate after an in-person assessment, and treat a price given over the phone as a guess rather than a bid.
What Brentwood Conditions Mean for ADU Construction
Brentwood sits in the East Bay / Contra Costa County, which means hot, dry inland summers with strong afternoon sun on west elevations, and cool nights that work every joint on the building. West-facing elevations take the worst of the afternoon sun in the Tri-Valley, so that is usually where we specify the higher grade and where the first failure shows.
Brentwood summers are among the hottest in the Bay Area — routinely 100°F+. Heat-rated materials are essential here.
ADU Construction Permits and Inspections in Brentwood
Brentwood's Community Development / Building Division reviews projects, with an efficient process for the city's newer housing. We handle permits and inspections.
Every ADU and addition needs a building permit, structural engineering and Title 24 energy compliance. State law requires the city to decide a complete ADU application within 60 days and waives impact fees on units under 750 square feet. We prepare the submittal, answer plan-check comments, coordinate utility connections and meet the inspector at each stage.
Where We Work in Brentwood
We take adu construction work across Brentwood, including Downtown Brentwood, Summerset, Trilogy, Pantages. Travel inside the city is included in the quoted price.
Brentwood at a Glance
Brentwood is a rapidly growing East Bay community on the eastern edge of Contra Costa County, with a large supply of relatively affordable single-family homes that owners are actively upgrading. We serve Brentwood with kitchen and bathroom remodels, flooring installation, siding, and exterior painting — all permitted through the City of Brentwood Building Division.
- Area: East Bay / Contra Costa County (ZIP 94513)
- Served from: our San Francisco branch, (415) 770-4977
- Permits issued by: Brentwood’s Building Division, applications through the Electronic Submittal Portal
- Typical Brentwood work: City of Brentwood permits; Kitchen and bathroom renovations — tract home upgrades; Siding and exterior painting
- Nearby cities we also serve: Antioch, Pittsburg, Oakley
