ADU Construction in Fremont: Regulations, Costs, and Lot Requirements

Why Fremont Is One of the Best Cities for ADU Construction

Fremont has earned a reputation as one of the most ADU-friendly cities in the East Bay. With nearly 230,000 residents, generous residential lot sizes, and a city government that actively streamlines the ADU permitting process, Fremont offers homeowners an unusually clear path to adding an accessory dwelling unit to their property.

The city’s approach combines practical regulatory support with genuine incentives. Fremont’s preapproved ADU program cuts review timelines in half. Ministerial approval eliminates the uncertainty of discretionary design review. And recent California state laws have expanded what homeowners can build, how they can use their ADUs, and even whether they can sell them as separate units.

This guide covers everything you need to know about building an ADU in Fremont: regulations, lot requirements, setbacks, costs, common lot types, popular designs, and the step-by-step permit process. Custom Home Design and Build has been constructing ADUs across the Bay Area since 2005, and Fremont’s East Bay market is one we serve regularly.

For a cost-focused breakdown, see our complete ADU cost guide for Fremont.

Fremont ADU Regulations: The Core Rules

Fremont’s ADU regulations are governed by a combination of the city’s municipal code (Ordinance 06-2023, adopted July 11, 2023) and California state ADU law. Here are the regulations that matter most.

No Minimum Lot Size

Fremont does not require a minimum lot size to build an ADU. If your property allows residential use and has an existing or proposed single-family home (or an existing multifamily building), you are eligible. This is a significant advantage over cities that impose lot area minimums.

Size Limits

ADU size limits in Fremont depend on your lot size and the type of ADU:

ADU Type	Lot Under 10,000 Sqft	Lot 10,000+ Sqft
Detached ADU	Up to 1,000 sqft	Up to 1,200 sqft
Attached ADU	50% of primary home or 1,000 sqft (whichever is less)	50% of primary home or 1,200 sqft (whichever is less)
Junior ADU (JADU)	Up to 500 sqft	Up to 500 sqft

For attached ADUs, the minimum allowable size is 850 sqft for a studio or one-bedroom and 1,000 sqft for two or more bedrooms, regardless of the 50% calculation. This state-mandated floor ensures homeowners can build a functional unit even on properties with a smaller primary residence.

Height Limits

ADU height limits in Fremont follow a tiered system:

• 16 feet is the base maximum height for detached ADUs
• 18 feet if the property is within half a mile of a major transit stop or on a multifamily lot
• 20 feet if the ADU’s roof pitch matches the primary home

Fremont’s proximity to BART stations (Fremont, Warm Springs/South Fremont, and Irvington) means many properties qualify for the 18-foot height allowance, which opens up two-story ADU designs.

Setback Requirements

All new ADUs must maintain:

• 4-foot side setbacks
• 4-foot rear setbacks
• Front yard setback per the underlying zoning district (varies by zone)

These setbacks do not apply to conversions of existing structures. If you are converting an existing garage that sits on the property line, you do not need to bring it into compliance with the 4-foot setback requirement.

Parking

Fremont does not require additional off-street parking for any ADU type. This applies to detached ADUs, attached ADUs, JADUs, and garage conversions. California state law waives parking requirements for ADUs within half a mile of a public transit stop, and Fremont extends this waiver citywide.

Number of Units Allowed

On a single-family lot, you can have:

• One ADU (detached or attached) plus one JADU

On multifamily properties, SB 1211 (effective January 2025) allows up to eight detached ADUs per lot, capped at the number of existing primary units. This law also eliminates the requirement to replace uncovered, off-street parking spaces demolished during ADU construction.

Lot Types and Zoning in Fremont

Understanding Fremont’s residential zoning districts helps you determine what is possible on your specific property.

R-1-6 (6,000 Sqft Minimum Lots)

The R-1-6 designation covers many of Fremont’s established neighborhoods, including parts of Centerville, Irvington, and central Fremont. Properties in these zones have minimum lot sizes of 6,000 sqft. On these lots, ADUs are limited to 1,000 sqft (since the lots fall below 10,000 sqft), but 1,000 sqft is still a generous two-bedroom unit. A detached ADU with 4-foot setbacks fits comfortably on most 6,000 sqft lots, particularly when the primary home leaves adequate rear yard space.

R-1-8 (8,000 Sqft Minimum Lots)

The R-1-8 zone requires 8,000 sqft minimum lots and covers neighborhoods including parts of Mission San Jose and Warm Springs. While still under the 10,000 sqft threshold for the larger ADU allowance, these lots offer more flexibility for positioning a detached unit while preserving usable yard space.

Larger Lots (10,000+ Sqft)

Properties in areas like Niles, parts of Mission San Jose, and the hillside neighborhoods often exceed 10,000 sqft. These lots unlock the full 1,200 sqft ADU allowance and provide the most flexibility for unit placement, yard retention, and design options. Many of these properties can comfortably accommodate a full-size detached ADU with a two-car garage conversion or an attached expansion as well.

Designated Neighborhoods

Fremont has designated neighborhoods with their own overlay requirements:

• Glenmoor Gardens (R-1-6-GG): 6,000 sqft minimum lots with neighborhood-specific standards
• Mission Ranch (R-1-8-MR): 8,000 sqft minimum lots with neighborhood-specific standards

ADU rules in these designated neighborhoods follow the same state-mandated regulations, but lot coverage and other zoning standards may differ. Check with Fremont’s Planning Division for property-specific guidance.

Popular ADU Designs for Fremont Properties

The right ADU design depends on your lot, your goals, and your budget. Here are the approaches that work best on Fremont properties.

Detached Backyard ADUs

Detached ADUs are the most common choice in Fremont. They offer complete separation from the primary home, which maximizes privacy for both the homeowner and the ADU occupant. This matters whether you are housing a family member, generating rental income, or creating a home office.

On Fremont’s 6,000-8,000 sqft lots, a well-designed detached ADU of 600-1,000 sqft fits in the rear yard while preserving a functional outdoor area. On 10,000+ sqft lots, a full 1,200 sqft unit with two bedrooms and two bathrooms is achievable.

Contemporary and modern designs are popular in Fremont, featuring clean lines, large windows, open-concept layouts, and efficient use of space. Many homeowners opt for a single-story structure that stays within the 16-foot height limit, keeping the scale subordinate to the primary residence.

Garage Conversions

Fremont’s no-parking-requirement policy makes garage conversions especially practical. A two-car garage (400-500 sqft) converts into a comfortable studio or one-bedroom unit. The existing structure, foundation, and roofing reduce construction costs significantly compared to building new.

Garage conversions are also exempt from the 4-foot setback requirement, since the structure already exists. This makes them viable even on properties where a new detached ADU would be difficult to position.

Attached ADUs

Attached ADUs work well on lots where rear yard space is limited. By building off the back or side of the primary home, you use the yard more efficiently and share one or more walls, reducing construction costs. In Fremont’s more compact Centerville and Irvington neighborhoods, attached designs are often the most practical option.

Junior ADUs (JADUs)

A JADU is built entirely within the existing or proposed single-family home, capped at 500 sqft. JADUs include an efficiency kitchen with cooking facilities and a food preparation counter. They share the primary home’s utilities, making them the least expensive option to build.

JADUs work well for homeowners who want to create an independent living space for a family member without building a separate structure. In Fremont, you can build a JADU in addition to a standard ADU, giving your property two secondary units.

ADU Construction Costs in Fremont

Here is what Fremont homeowners are paying in 2026:

ADU Type	Cost Range	Timeline
Garage Conversion	$100,000-$150,000	4-6 months
JADU	$80,000-$140,000	3-5 months
Attached ADU	$150,000-$320,000	6-10 months
Detached ADU	$260,000-$460,000+	8-14 months

What Drives Costs

Several factors influence where your project falls within these ranges:

• Size. Every additional square foot adds $300-$500 depending on complexity and finishes.
• Foundation. Detached ADUs require new foundation work, which can range from $15,000 to $40,000+ depending on soil conditions and engineering requirements.
• Utility connections. Extending water, sewer, gas, and electrical to a detached unit adds $10,000-$30,000 or more. Attached ADUs and JADUs benefit from proximity to existing connections.
• Finish level. Standard builder-grade finishes keep costs at the lower end. Custom cabinetry, high-end fixtures, premium flooring, and designer tile push costs higher.
• Site conditions. Sloped lots, poor soil, limited access for equipment, and proximity to heritage trees all increase costs.

Permit Fees

Fremont ADU permit fees range from $5,000 to $10,000 for a standard application. Homeowners using a preapproved ADU plan pay a flat plan review fee of $1,000, with construction and inspection fees varying by plan. Impact fees for ADUs under 750 sqft are waived under California state law. For larger units, Fremont’s impact fees can reach $75,000, which is among the higher figures in the Bay Area. Factoring impact fees into your budget early is essential.

For a detailed cost breakdown by ADU type, see our Fremont ADU cost guide.

The Fremont ADU Permit Process

Fremont’s ADU permitting process is straightforward compared to many Bay Area cities. All ADUs are approved ministerially, meaning there is no discretionary design review, no planning commission hearing, and no neighbor notification requirement.

Step 1: Property Assessment and Design

Before applying for permits, assess your property’s zoning district, lot size, setbacks, existing structures, and utility access. This determines what type and size of ADU is feasible. At Custom Home, this evaluation happens during our Phase 1 design process. We survey the site, map constraints, and develop 3D visualizations so you see exactly what the finished ADU will look like before construction begins.

Step 2: Plan Preparation

You will need complete construction drawings, including architectural plans, structural engineering, Title 24 energy compliance, and site plans showing the ADU’s position relative to property lines and existing structures. If you choose one of Fremont’s preapproved ADU plans, the architectural plans are already city-approved and ready to submit.

Step 3: Application Submittal

Submit your application to Fremont’s Community Development Department. The application includes your plans, completed forms, and applicable fees.

Step 4: Plan Review

Fremont reviews standard ADU applications within 15 business days. Preapproved ADU plans are reviewed in 7 business days. The city checks for compliance with building codes, zoning requirements, and fire safety standards.

If corrections are needed, the city issues a correction notice. Revise and resubmit. Most well-prepared applications clear review in one or two cycles.

Step 5: Permit Issuance and Construction

Once approved, you receive your building permit and construction can begin. Throughout construction, the city conducts inspections at key milestones: foundation, framing, rough plumbing and electrical, insulation, and final inspection.

Step 6: Certificate of Occupancy

After passing final inspection, the city issues a certificate of occupancy. Your ADU is legally complete and ready for use.

Total Timeline

Plan for 8-14 months from initial design through completed construction for a detached ADU. Garage conversions and JADUs typically complete in 3-6 months.

California State ADU Laws That Affect Fremont Homeowners

Several recent state laws expand ADU opportunities for Fremont property owners.

AB 1033: ADU Condo Conversion

Effective since January 2024, AB 1033 authorizes local governments to adopt ordinances allowing homeowners to sell ADUs as separate condominiums. This means you could potentially sell your ADU independently from your primary home. Cities including San Jose, Santa Monica, and San Diego have already adopted such ordinances. If Fremont follows suit, this creates a new homeownership pathway in one of the Bay Area’s most competitive housing markets.

SB 1211: Multifamily ADU Expansion

SB 1211 allows up to eight detached ADUs per lot on multifamily properties, capped at the number of primary units. It also eliminates the requirement to replace uncovered parking spaces demolished during ADU construction and introduces a clearer definition of “livable space.”

Additional 2025 Laws

Governor Newsom signed four additional ADU bills in 2025 (AB 462, AB 1154, SB 9, and SB 543) that further streamline permitting, expand coastal zone ADU approvals, and clarify ADU development standards statewide.

For a full breakdown of current state ADU legislation, see our 2026 California ADU laws guide.

Why Work with Custom Home Design and Build

Building an ADU in Fremont involves coordinating design, engineering, permitting, and construction across multiple city departments and state requirements. Custom Home Design and Build handles the entire process under one roof.

Our two-phase approach gives you clarity before construction begins:

Phase 1 (Design): We assess your lot, determine the optimal ADU type and placement, develop architectural plans and 3D visualizations, and prepare a detailed, itemized budget. You approve the final design with full visibility into costs and timeline.

Phase 2 (Build): We handle permitting, construction, inspections, and final occupancy. Because every detail is resolved in Phase 1, there are no mid-build surprises, no budget overruns, and no schedule delays from plan revisions.

As a design-build firm, we eliminate the coordination gaps that arise when homeowners hire an architect and a contractor separately. One team, one contract, one point of accountability from start to finish.

Start Your Fremont ADU Project

Whether you are considering a backyard detached ADU, a garage conversion, or a JADU for a family member, Fremont’s regulations and permitting process are designed to support your project. The key is starting with a clear understanding of what your lot allows and what the project will cost.

Ready to explore what is possible on your Fremont property? Contact Custom Home Design and Build for a consultation. We will evaluate your lot, walk through the regulations specific to your property, and help you determine the best ADU approach for your goals and budget.