ADU Costs in Fremont: A Complete 2026 Breakdown

ADU Costs in Fremont: What to Expect in 2026

Fremont sits at the heart of the East Bay, offering a combination that makes it ideal for ADU construction: generous lot sizes, strong rental demand, and a city government that actively supports accessory dwelling units. With a population of nearly 230,000, Fremont is one of the largest cities in the Bay Area and one of the most diverse, with a thriving community that continues to attract families and professionals.

This guide breaks down 2026 ADU costs specific to Fremont: what each type costs to build, what you will pay in permits and fees, what drives costs up or down, and how to plan your budget. Custom Home Design and Build has been building ADUs across the Bay Area since 2005, and Fremont’s East Bay market is one we know well.

For Bay Area-wide ADU pricing, see our ADU cost guide.

Cost by ADU Type

The type of ADU you build is the single biggest factor in your total cost. Here is what Fremont homeowners are paying in 2026:

ADU Type	Cost Range	Cost/Sqft	Timeline	Typical Size
Garage Conversion	$100,000-$150,000	$150-$330	4-6 months	400-500 sqft
Attached ADU	$150,000-$320,000	$280-$430	6-10 months	400-800 sqft
Detached ADU	$260,000-$460,000+	$330-$480	8-14 months	500-1,200 sqft
Junior ADU (JADU)	$80,000-$140,000	$180-$330	3-5 months	200-500 sqft

These ranges cover construction costs. Permits, design fees, and utility connections are additional expenses covered in the sections below.

Garage Conversions: The Most Affordable Option

Garage conversions are the most budget-friendly ADU type in Fremont because the structure already exists. You skip foundation work, framing, and roofing. The core investment goes toward insulation, drywall, flooring, a kitchen, a bathroom, plumbing, electrical upgrades, and HVAC.

In Fremont, a one-car garage conversion (250-400 sqft) runs $80,000-$110,000. A two-car garage (400-600 sqft) costs $100,000-$150,000. Since Fremont does not require additional parking for ADUs, converting your garage will not create a compliance issue. That said, plan for off-street parking alternatives if you currently rely on the garage for vehicles.

Mid-range conversions with upgraded electrical systems, better-quality finishes, and more extensive plumbing typically land in the $100,000-$130,000 range. High-end conversions with premium finishes and advanced features can push past $150,000.

Attached ADUs

Attached ADUs connect to the main house, sharing at least one wall. This makes utility connections simpler and reduces foundation and roofing costs compared to a fully detached unit. In Fremont, attached ADUs work well on tighter lots, particularly in neighborhoods like Irvington and Centerville where parcels are more compact.

Expect to pay $150,000-$320,000 for an attached ADU in Fremont. The wide range reflects differences in size (400-800 sqft), the complexity of integrating with the existing structure, and finish level.

Detached ADUs

Detached ADUs are standalone structures, completely separate from your main home. They offer maximum privacy and rental potential. In Fremont, a detached ADU costs $260,000-$460,000+.

Fremont’s neighborhoods offer varying lot sizes. Areas like Niles, Mission San Jose, and parts of Warm Springs tend to have larger parcels (7,500+ sqft), giving homeowners ample room for a full-size detached ADU. Many properties in these areas can comfortably accommodate a 1,000-1,200 sqft unit while meeting the 4-foot side and rear setback requirements.

Fremont ADU Permit Fees and Soft Costs

Construction is only part of the total budget. Here are the other costs Fremont homeowners should plan for:

Cost Category	Typical Range	Notes
Building permit fees	$5,000-$10,000	Based on project scope and valuation
Plan review (preapproved plans)	$1,000 flat fee	Plus additional construction and inspection fees
Architectural/design fees	$8,000-$22,000	Plans, engineering, Title 24 energy compliance
Utility connections	$5,000-$15,000	Water, sewer, electrical; detached ADUs cost more
Impact fees (750+ sqft)	$5,000-$12,000	Applicable for units 750 sqft and above
Impact fees (under 750 sqft)	$0	Waived under California law
Survey and soils report	$2,000-$5,000	Required for new detached structures
Landscaping and site restoration	$3,000-$10,000	Yard restoration, fencing, hardscaping

Total soft costs typically add $20,000-$55,000 on top of construction, depending on the project.

Fremont’s Preapproved ADU Plans

One of Fremont’s standout programs is its preapproved ADU plan library. The city has reviewed and approved plans from designers, architects, and builders that meet all zoning and building code requirements. Choosing a preapproved plan offers two major advantages:

• Faster review. Preapproved plans are reviewed in 7 business days, compared to 15 business days for standard applications.
• Lower plan review costs. Applicants pay a flat plan review fee of $1,000 instead of the standard rate. Additional construction and inspection fees still apply and vary by the plan selected.

If a preapproved plan fits your lot and goals, it can shave weeks off your timeline and reduce upfront soft costs.

What Drives ADU Costs in Fremont

Size and Layout Complexity

Cost per square foot drops as the ADU gets larger, but total cost increases. A 500 sqft ADU costs less overall than a 1,000 sqft unit, but the per-square-foot rate is higher because fixed costs (kitchen, bathroom, utility hookups) are spread over less area. In Fremont, expect $350-$480 per sqft for smaller units (under 600 sqft) and $300-$380 per sqft for larger units (800-1,200 sqft).

Foundation and Site Conditions

Detached ADUs need new foundations. Fremont’s geography ranges from flatland neighborhoods near the bay to the foothills of Mission San Jose. Properties closer to the bay may have softer soils and higher water tables, which can increase foundation costs. Hillside properties in Mission San Jose may require additional grading and retaining work. A soils report ($2,000-$4,000) will tell you what to expect before construction starts.

Finish Level

The gap between basic and premium finishes can be $40,000-$90,000 on the same-size ADU.

Finish Level	Description	Added Cost vs. Standard
Standard	Laminate countertops, vinyl flooring, builder-grade fixtures	Baseline
Mid-range	Quartz countertops, LVP flooring, upgraded fixtures, tile backsplash	+$15,000-$30,000
High-end	Stone countertops, hardwood flooring, custom cabinetry, premium appliances	+$35,000-$70,000+

Most Fremont homeowners building for rental income choose mid-range finishes. Those building ADUs for aging parents or extended family tend to invest in higher-end finishes and accessibility features for long-term comfort.

Utility Connections

Attached ADUs and garage conversions share utility infrastructure with the main house, keeping connection costs low ($5,000-$8,000). Detached ADUs require independent lines for water, sewer, and electrical, running $10,000-$15,000 or more. California law requires a separate electrical panel for metering in all ADUs.

Fremont ADU Regulations to Know

Understanding the rules before you plan saves time and money. Here are the key Fremont ADU regulations for 2026:

• Allowed zones. ADUs are permitted in all zoning districts that allow residential use, including single-family, multifamily, and mixed-use zones.
• Maximum size. Detached ADUs up to 1,200 sqft. Attached ADUs up to 50% of the primary dwelling or 1,200 sqft, whichever is less.
• Setbacks. 4 feet from side and rear property lines for all new ADU construction.
• Parking. No additional parking is required for ADUs in Fremont.
• Design review. Fremont does not require ADUs to match the main home’s design. All ADU applications are approved ministerially with no discretionary review.
• Owner occupancy. No owner-occupancy requirement for ADUs built between January 1, 2020, and January 1, 2025. Owner occupancy is required for properties with JADUs.
• One ADU plus one JADU per lot. You can build both on a single-family property.

Fremont adopted the 2025 California Building Code effective January 1, 2026. Your project must comply with the updated energy, structural, and fire safety requirements. Working with a builder who stays current on code changes ensures your plans are compliant from day one.

How Fremont Compares to Other Bay Area Cities

Fremont’s East Bay location gives it a cost advantage over Peninsula and premium South Bay cities. Here is how a typical 600 sqft detached ADU compares:

City	Estimated Cost	Permit Timeline	Key Difference
Fremont	$260,000-$360,000	8-12 weeks	Preapproved plans, no design review
San Jose	$250,000-$350,000	6-10 weeks	Reduced fees, ADU Ally support
Sunnyvale	$270,000-$380,000	8-12 weeks	Standard processing
Cupertino	$290,000-$400,000	8-14 weeks	Higher finish expectations
Palo Alto	$320,000-$450,000	10-16 weeks	Design review adds time and cost

Fremont costs run roughly 10-15% lower than premium Peninsula cities like Palo Alto and 5-10% lower than West Bay markets like Cupertino. East Bay labor rates and material sourcing contribute to the savings. The city’s streamlined ministerial approval process also helps keep soft costs predictable.

Sample ADU Budgets for Fremont

Budget Example: 450 sqft Garage Conversion

Line Item	Cost
Construction	$105,000
Building permits	$5,000
Design and engineering	$8,000
Utility upgrades	$5,000
Landscaping/site restoration	$3,000
Total	$126,000

Budget Example: 800 sqft Detached ADU

Line Item	Cost
Construction	$310,000
Building permits	$8,000
Design and engineering	$18,000
Utility connections	$12,000
Impact fees (over 750 sqft)	$7,000
Survey and soils report	$3,500
Landscaping/site restoration	$6,000
Total	$364,500

These are mid-range estimates. Your final number will depend on your lot conditions, finish selections, and any site-specific challenges.

Rental Income Potential in Fremont

Fremont’s strong rental market makes ADUs an attractive investment. Average rents in Fremont run approximately $2,800 per month for a one-bedroom apartment as of early 2026, with studios around $2,065 and two-bedroom units near $3,050. ADU rents vary based on size, finishes, and whether the unit has a private entrance, but a well-built 500-600 sqft one-bedroom ADU can realistically command $2,200-$2,800 per month.

At $2,500 per month in rent, an ADU generates $30,000 per year in gross income. On a $360,000 investment, that represents roughly an 8% gross return before expenses. Fremont’s proximity to Tesla’s manufacturing facility in the Warm Springs district, plus strong tech employment across the East Bay corridor, supports consistent rental demand.

Fremont’s median home value sits at approximately $1.6 million. A well-built ADU can increase property value by $150,000-$280,000, depending on quality and configuration. Combined with rental income, many Fremont homeowners see a full return on their ADU investment within 8-12 years.

How to Control Your ADU Budget

Lock in Pricing During Design

The biggest source of budget overruns is starting construction before the scope is fully defined. At Custom Home, our two-phase process separates design from construction. During Phase 1, we create full 3D renderings and lock in every material selection and line item. You approve the final number before a single shovel hits the ground.

Right-Size Your ADU

Bigger is not always better. A well-designed 600 sqft ADU can feel spacious and rent for nearly as much as an 800 sqft unit. Staying under 750 sqft also eliminates impact fees, saving you $5,000-$12,000 in Fremont.

Consider Preapproved Plans

Fremont’s preapproved ADU plans save on both time and money. The $1,000 flat plan review fee and 7-day review timeline reduce upfront costs and uncertainty. If a preapproved design fits your lot, it can be a smart starting point.

Work With a Builder Who Knows the East Bay

Fremont’s neighborhoods vary significantly, from flatland areas near the bay to hillside properties in Mission San Jose. A builder who knows these conditions can flag potential issues early, recommend the right foundation approach, and keep your project on schedule.

Why Fremont Homeowners Choose Custom Home

Custom Home Design and Build has been building ADUs, custom homes, and remodels across the Bay Area since 2005. Our design-build approach means one team handles architecture, permitting, and construction, so nothing falls through the cracks.

For ADU projects, our process works like this:

1. Free consultation. We assess your lot, discuss your goals, and provide a realistic budget range.
2. Phase 1: Design. Full architectural plans, 3D renderings, material selections, and a locked-in construction price.
3. Phase 2: Build. Permitted construction with weekly progress updates and a dedicated project manager.

Every detail is decided before we build. No surprises, no change orders, no budget creep.

Start Your Fremont ADU Project

Fremont’s combination of generous lot sizes, a streamlined permitting process, strong rental demand, and lower East Bay construction costs makes it one of the best cities in the Bay Area for an ADU investment. Whether you are converting a garage, building a detached unit in your backyard, or adding an attached suite for family, the key is starting with a clear plan and accurate numbers.

Ready to explore what an ADU would cost on your specific property? Contact Custom Home for a free consultation. We will visit your site, discuss your goals, and give you a realistic budget based on your lot, your neighborhood, and your vision.