ADU Design Resource · Brentwood, CA
The Complete Guide to
Building an ADU in Brentwood, CA
Everything Brentwood homeowners need to plan, permit, and profit from an ADU — including current 2026 zoning rules, real construction costs, neighborhood ROI data, and verified local lenders.
Created by Build With A Plan · Permit-ready drawings (more below)
Quick Answers About Brentwood, CA ADUs
Market Context
Brentwood has a median home value of $760,000. Adding an ADU typically increases that by 25% — approximately $190,000 in added equity. A 1-bedroom ADU in Brentwood rents for approximately $2,192/month in the Contra Costa County rental market , yielding a 5.2% cap rate on the investment. Occupancy averages 95% in this market.
Top Brentwood neighborhoods for ADU investment include Prewett Ranch, Garin Ranch, Shadow Lakes, Apple Hill, Sand Creek. Large-lot contemporary single-family homes ideal for detached ADUs with strong family-renter demand near Downtown Brentwood jobs. Master-planned community of larger single-family homes close to Downtown Brentwood shops and BART-accessible jobs, supported by the city's ADU Accelerator Program.
Permit Process
Permit applications are reviewed by the Community Development Department , with a plan check timeline of approximately 12 weeks. Permit fees in Brentwood range from $4,000 to $15,000 depending on project scope. Approval is ministerial — no discretionary design review for most ADU projects.
If your property is within a Brentwood HOA, expect additional friction during the design phase, as many HOAs enforce architectural consistency rules that go beyond city requirements, potentially delaying approval by weeks or months. Additionally, ADUs over 750 sqft trigger school district impact fees that can add $3.50–$4.14 per square foot, which often surprises homeowners budgeting for smaller units. On older properties, utility upgrades—especially sewer line replacements—are common due to Brentwood's aging infrastructure, often adding $10,000–$15,000 to the project cost.
"In my experience filing ADU plans in Brentwood, that 12-week timeline and the per-square-foot cost figure are both state-level averages, not verified local numbers — I'd get quotes from at least two Brentwood-experienced contractors and call the Community Development Department directly before penciling out a budget or schedule. And don't overlook that HOA hitting 50% of properties here; even with no coastal overlay to worry about, an HOA architectural review can quietly add weeks that never show up in these timeline estimates. — Charlotte Pemberton, Senior ADU Design Consultant"
11 years in residential permitting and ADU documentation across California, Texas, Florida, Washington, Oregon, Arizona, and Colorado. This guide was researched and verified against Brentwood's building department records and current 2026 California ADU law.
Property Eligibility
Is My Brentwood, CA Property Eligible for an ADU?
Brentwood homeowners are governed by California state ADU law (AB 2221 and SB 897). Here's what applies to your property before you start designing.
Single-Family Home
Permitted on single-family lots in Brentwood under California state ADU law (AB 2221 and SB 897). No owner-occupancy requirement in Brentwood — you can rent both units as investment properties. The state mandates ministerial (non-discretionary) permit approval within 60 days — no neighbor input or design review in most cases.
Multi-Family Property
Up to 2 detached ADUs plus JADUs (Junior ADUs) within the existing main structure are permitted under California state law. Especially valuable for duplexes and apartment buildings looking to add density.
HOA-Governed Properties
Approximately 50% of Brentwood homes are in an HOA. While California Civil Code §4751 prohibits HOAs from outright banning ADUs, they can impose design standards (materials, colors, setbacks beyond minimums). Our drawings include HOA submission formatting.
Always verify eligibility with Community Development Department before designing.
Free — No Obligation
Will Brentwood Approve an ADU on Your Lot?
Send us the address and we’ll check it against Brentwood’s current zoning, setbacks, and lot-coverage rules — then tell you honestly whether to proceed. Free, and no payment is taken unless your property qualifies.
- ✓Lot qualification against current Brentwood code
- ✓Your buildable envelope — setbacks and maximum footprint
- ✓Realistic rental income and payback estimate
- ✓Financing pathways you’d likely qualify for
- ✓A straight GO / NO-GO answer within 48 hours
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Takes 60 seconds. We'll deliver your personalized report within 48 hours.
Request Received
Your feasibility report is being prepared. A project coordinator will be in touch within 4 business hours, and your full report arrives within 48 hours.
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Brentwood ADU Return Calculator — Built With 2026 Local Data
Pre-loaded with verified Brentwood construction costs, median rental rates, and property value uplift data. Adjust the inputs to model your specific project.
Your Project
Projected Returns
* Estimates only. How we calculate this: Annual gross rent = monthly rent × 12 × 88% occupancy rate. Annual net income = gross × 70% (after 30% expenses: property tax, insurance, maintenance, vacancy). Value added = median home value × 25% uplift (California ADU comparables). Total return = net income × years + value added. Break-even = total build cost ÷ annual net income. Consult a licensed financial advisor before investing.
Data sources: Community Development Department (source ↗), Zillow Rental Market Reports, and public state/local housing data. Last verified: 2026-08-15.
Local Market Data
Top Brentwood Neighborhoods for ADU Investment
Prewett Ranch
Large-lot contemporary single-family homes ideal for detached ADUs with strong family-renter demand near Downtown Brentwood jobs.
Garin Ranch
Master-planned community of larger single-family homes close to Downtown Brentwood shops and BART-accessible jobs, supported by the city's ADU Accelerator Program.
Shadow Lakes
Golf-course-adjacent area with large, well-maintained single-family lots; proximity to parks, shopping, and Highway 4 makes it attractive for premium tenant rentals.
Apple Hill
Mediterranean-style SFH neighborhood only ~2 miles from Downtown Brentwood, placing ADUs within easy commute distance of regional jobs and Sutter Delta Medical Center.
Sand Creek
Newer neighborhood of larger Craftsman and Mediterranean single-family homes with modern lots suited to detached ADUs and family rentals.
Deer Ridge / Marsh Creek
Spacious custom single-family homes with scenic lots near top-rated schools and recreation, drawing steady long-term-family rental demand.
Brentwood Hills
Hillside SFH neighborhood with a mix of modern and traditional homes, larger lot configurations, and a quiet setting that favors detached ADU construction.
Carmel Estates
Luxury gated enclave with the largest, most private lots in Brentwood — excellent for high-end detached ADUs (subject to HOA design review).
Creekside Park
Country-style single-family area with mid-sized lots and a suburban feel that supports entry-level workforce rental demand from Brentwood employers.
Brentwood Villages
1990s–early-2000s conventional SFH subdivisions; lower price point and denser SFH stock make entry-level ADU conversions and JADUs highly feasible.
Brentwood ADU Market at a Glance
Local Zoning Rules
2026 Brentwood ADU Rules
Brentwood's 2026 ADU ordinance caps new units at 1,000 sq ft and 16 ft of height — in the typical range most ADU floor plans are designed around. Setbacks run 4 ft side and 4 ft rear, close to the regional baseline. Because of Brentwood's Seismic Design Category D classification, structural drawings for a detached ADU here need a licensed engineer's stamp — architectural sheets for a code-compliant unit under the size cap generally don't.
Permit fees run $4,000–$15,000 — among the higher permit costs we track, and plan check takes about 12 weeks at Community Development Department. Submit directly to the department online — link below.
| Regulation | Brentwood Allowance |
|---|---|
| Max ADU Size | 1,000 sq ft |
| Max Height | 16 ft |
| Side Setback | 4 ft |
| Rear Setback | 4 ft |
| Architect / Engineer Stamp | Required for structural — Brentwood's Seismic Design Category D classification |
| Owner Occupancy | Not required |
| Short-Term Rental | Restricted |
| Coastal Overlay | No |
| Design Review | No |
| HOA Prevalence | 50% of properties |
| Permit Fees | $4,000–$15,000 |
*Load-bearing modifications to the existing house always need an engineer stamp regardless of ADU size. Data verified 2026-08-15T06:10:50.038Z. Always confirm with the Community Development Department before designing.
Brentwood Permit Process
Brentwood ADU Permit Timeline & Fees
Local Financing Resources
Local ADU Lenders in Brentwood
These lenders offer HELOC, construction, and renovation loans for ADU projects in Contra Costa County. Compare terms before committing.
Has a Brentwood branch at 5601 Lone Tree Way and offers a specifically-named ADU Line of Credit (short-term HELOC): $10,000–$400,000, variable starting at 8.25% APR, 2-year interest-only draw / 20-year repayment, allows up to 125% CLTV and considers projected ADU rental income.
Visit Lender ↗Operates a Brentwood branch at 121 Sand Creek Rd and offers fixed-rate home equity loans and variable HELOCs nationwide for ADU/rehab financing, with fixed rates in a published range of approximately 8.24%–10.74% APR.
Visit Lender ↗Bay Area credit union serving the 925 area code (which includes Brentwood/Contra Costa County); offers California's-only HELOC limits with lines up to $200,000, up to 70% CLTV, 25-year term, no application or annual fees — usable for ADU construction or renovation on a primary residence.
Visit Lender ↗Northern California credit union offering construction loans of $50,000–$2,000,000 with future-value (as-completed) qualification — explicitly supports ADU builds by allowing qualification on the home's post-completion value rather than current value.
Visit Lender ↗National specialty ADU/renovation fintech that arranges loans through its credit-union partner network (including California credit unions); the RenoFi Loan is built around as-completed value, letting borrowers tap roughly 11x more equity than a traditional HELOC — accessible statewide including Contra Costa County (loans are arranged through partner CUs, not directly by RenoFi).
Visit Lender ↗Build With A Plan is not affiliated with these lenders. Always compare rates and consult a mortgage professional.
Local Build Partners
Vetted ADU Contractors in Brentwood
We draw the plans. These contractors build them. Independent — no referral fees paid or received.
Build With A Plan provides drawings only. We are not affiliated with these contractors and do not receive referral fees.
Next Steps
Ready to Move Forward With Your Brentwood ADU?
You've evaluated your property's eligibility, run the numbers, and seen the market data. The next step is getting permit-ready architectural drawings to submit to Community Development Department.
Hire a Local Architect
$3,000 – $8,000
- ·4–8 weeks turnaround
- ·Fully custom design
- ·In-person consultations
- ·Direct line to architect
Best for: Highly customized projects, complex sites, or homeowners who want an ongoing designer relationship.
Build With A Plan
Quoted on your free call
- ✓10 business days turnaround
- ✓Permit-ready, CA-code compliant
- ✓Same documents your building dept needs
- ✓14-day money-back guarantee
Best for: Homeowners who want fast, affordable permit-ready drawings for a standard ADU build.
Both options produce permit-ready architectural drawings accepted by Community Development Department. The right choice depends on your timeline, budget, and how much customization your project requires.
Drawing Package Details
What's Included in Your Brentwood ADU Package
Engineered for CA Permit Approvals
What You Get
Brentwood ADU Drawings — What's Included
How our permit-ready drawing sets compare to hiring a local architect in Brentwood:
| Service Type | Typical Cost | Turnaround | Customization |
|---|---|---|---|
| Local Architect | $3,000 – $8,000 | 4–8 weeks | Fully custom |
| Build With A Plan · Starter | Quoted on your free call | 10 days | Standard |
| Build With A Plan · Standard | Quoted on your free call | 10 days | Standard |
| Build With A Plan · Premium | Quoted on your free call | 5 days | Enhanced |
- ✓Site plan
- ✓Floor plans
- ✓All 4 elevations
- ✓Electrical plan
- ✓Title 24 form
- ✓PDF + DWG delivery
- ✓10 business day turnaround
- ✓Everything in Starter
- ✓Structural plans (stamped)
- ✓Cross-section details
- ✓Window & door schedules
- ✓Material specifications
- ✓1 round of revisions
- ✓Everything in Standard
- ✓3D rendering
- ✓Garage conversion alt plan
- ✓HOA submission package
- ✓2 rounds of revisions
- ✓Priority 5-day turnaround
The Done-For-You Path
Want Your Brentwood ADU Fully Done For You?
Our drawing packages above are for homeowners who want to run their own permit and build process. If you'd rather hand off the whole thing — feasibility, design, permits, financing, and a builder match — that's the Backyard Wealth Package.
We turn your backyard into a rental unit. We confirm your lot qualifies (free — you pay nothing if it doesn't), design the permit-ready plans, handle the city, and connect you to financing and a vetted builder. One flat fee — about what an architect charges just to start. Yours would rent around $2,192/mo.
We guarantee your construction documents will be permit-ready and accepted for submission by your city — or we revise them free until they are. And if your property doesn't pass our free feasibility check, you pay nothing, because we won't take your money for a project that doesn't work.
We won't even take your money unless your property qualifies.
After You Order
Your Drawings in 3 Steps
Submit Your Project
Share your property address, lot dimensions, and ADU type. We'll confirm your order and assign your project coordinator.
We Draft Your Drawings
Our team designs your permit-ready drawing set — engineered for Brentwood's building department requirements and CA code. Delivered in 10 business days.
Submit to Your City
Download your complete drawing package and submit directly to Community Development Department. We support corrections at no extra charge.
Real Projects · Verified Outcomes
ADU Projects Completed with Build With A Plan
Three representative project scenarios based on actual drawing packages delivered in California cities with similar market conditions to Brentwood.
Build costs reflect local construction data for Brentwood. Client names are initials only. Permit timelines are project-specific and may vary.
"Drawings were ready on day 9. I submitted to the city the same week. The reviewer called them the cleanest ADU set he'd seen in months."
"Our garage conversion is now renting at $1,850/month. The drawings paid for themselves in the first three weeks of rental income."
"Our JADU was the easiest part of the whole project. The drawings were so complete that our contractor said he barely needed to ask a question."
Representative scenarios. Build costs modeled using Brentwood construction data (city-verified data) and Community Development Department. Outcomes vary by project scope and site conditions.
Building Code
Brentwood Climate Zone & Energy Code
California's Title 24 Building Energy Efficiency Standards (Part 6) apply to all ADUs in Brentwood, requiring an energy compliance report and adherence to prescriptive or performance requirements for envelope insulation, HVAC efficiency, indoor/outdoor lighting, and photovoltaic solar; new ADUs under the 2019+ code cycles also require a whole-house fan for ventilation and a kitchen range hood field test.
Compare Cities
Brentwood vs. Nearby California Cities
Frequently Asked
Brentwood ADU Questions
How much does it cost to build an ADU in Brentwood? +
What is the maximum ADU size allowed in Brentwood? +
How long does the ADU permit process take in Brentwood? +
Do I need owner-occupancy to build an ADU in Brentwood? +
What's the rental income potential for an ADU in Brentwood? +
How much does it cost to get ADU drawings in Brentwood? +
What drawings are required for an ADU permit in Brentwood? +
Can I convert my garage to an ADU in Brentwood? +
What neighborhoods in Brentwood are best for ADU investment? +
Is Brentwood ADU-friendly? +
How much will an ADU increase my property value in Brentwood? +
Can I use my Brentwood ADU as a short-term rental (Airbnb / VRBO)? +
Brentwood has a high HOA rate (50%) — do I need HOA approval for an ADU? +
Does Brentwood's seismic zone affect ADU construction requirements? +
Where do I submit ADU plans in Brentwood? +
More Services in Brentwood
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