Accessory Dwelling Units (ADUs) Construction Services in Ontario, California

Empowering Homeowners with Smarter ADU Construction Solutions

In Ontario, California, and nearby areas, including Corona, Claremont, West Covina, Arupa, and Miraloma, ABL Contracting has been a trusted name in construction excellence for over 50 years. As a full-service general contractor, we specialize in designing and building Accessory Dwelling Units (ADUs) that bring value, flexibility, and modern living convenience to homeowners. Whether you’re looking to create an income-generating rental unit or expand your family’s living space, our experienced team brings craftsmanship and regulatory expertise together for flawless results.


The demand for ADUs has surged across Southern California as property owners seek affordable, sustainable, and space-efficient housing solutions. Ontario’s growing population and proximity to Los Angeles County make it an ideal location for homeowners to take advantage of ADU opportunities. We ensure that every project aligns with the city’s zoning codes, building requirements, and architectural standards, thereby enhancing both function and property value. From detached backyard cottages to attached suite conversions, our approach is rooted in precision, compliance, and long-term durability.


With ABL Contracting, homeowners can expect a seamless and transparent experience from consultation to completion. Our deep understanding of San Bernardino County’s local building regulations and permit processes helps homeowners avoid costly delays. Every ADU project is tailored to the property’s unique footprint, aesthetic, and intended use. By combining innovative design, high-quality materials, and skilled project management, we make ADU development in Ontario and its neighboring areas not only feasible but rewarding.

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Our Services

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Our Comprehensive ADU Services

  • Detached ADU Construction

    We specialize in building fully independent backyard units that serve as private living spaces or rental properties. Each detached ADU features its own utilities, entrance, and amenities, providing complete autonomy from the main home. Our experts manage design, permitting, and construction, ensuring compliance with local codes while maximizing your property’s usable space for functional, stylish living.

  • Attached ADU Additions

    Attached ADUs extend directly from the existing structure, offering added space for guests or extended family. We handle seamless integration with your home’s architectural style, electrical, and plumbing systems. From structural engineering to finish work, our team ensures every addition feels like a natural, cohesive part of your residence while adding significant value to your property.

  • Garage Conversions

    Converting an underused garage into a modern living unit is one of the most cost-effective ADU options. We transform existing garages into fully insulated, code-compliant dwellings complete with kitchens, bathrooms, and living areas. This service helps homeowners make the most of existing square footage without extensive new construction, creating functional spaces ideal for guests, tenants, or home offices.

  • Basement ADU Conversions

    Transform your basement into a livable, rentable unit through our specialized ADU conversion service. We handle moisture-proofing, egress installation, and utility integration to meet all safety and zoning requirements. The result is a comfortable, efficient living space that enhances your property’s versatility and boosts its overall resale value.

  • ADU Design and Permitting

    Our team provides full architectural design, planning, and permitting support for ADU construction. We handle site evaluations, zoning compliance, and design approvals with local authorities. By managing the bureaucratic and technical steps, we simplify the process for homeowners, ensuring each ADU project moves efficiently from concept to construction.

  • Energy-Efficient ADU Upgrades

    We integrate sustainable technologies into every ADU, including solar-ready systems, LED lighting, efficient HVAC, and water-saving fixtures. These energy-efficient upgrades reduce operational costs and support eco-friendly living. Our focus on sustainability not only enhances comfort and functionality but also aligns with California’s energy conservation goals and green building standards.

Benefits of Professional ADU Construction

Increased Property Value

An expertly built ADU significantly boosts property value by adding independent, functional living space. Buyers and investors increasingly seek homes with flexible housing options, making properties with ADUs more marketable and profitable in resale scenarios. A professional build ensures compliance, durability, and aesthetic quality that enhances long-term investment potential.

Rental Income Opportunities

Adding an ADU opens a consistent stream of passive income through long-term or short-term rentals. Properly constructed and permitted units command competitive rents, offsetting mortgage costs or generating additional revenue. With quality workmanship and compliant design, property owners can secure reliable tenants and maximize their return on investment.

Family Flexibility and Comfort

An ADU provides ideal accommodation for aging parents, adult children, or visiting guests without compromising privacy. Professionally designed units offer independent living spaces with accessibility features tailored to multigenerational households. The flexibility of design and function improves lifestyle convenience while keeping family members close and comfortable.

Compliance and Peace of Mind

Professional construction guarantees adherence to Ontario’s building codes, safety standards, and zoning ordinances. Proper permits and inspections reduce legal risks, future liabilities, and costly rework. Homeowners gain confidence knowing their ADU meets every local requirement for occupancy, safety, and property integration, ensuring smooth approval and long-term reliability.

Optimized Space Utilization

A professionally planned ADU maximizes every inch of your property, whether through vertical expansion, compact layout design, or creative conversions. High-quality design and engineering ensure functionality without sacrificing comfort or aesthetics. Proper space utilization enhances both property appeal and efficiency, allowing homeowners to make the most of their real estate investment.

Sustainable Living and Energy Savings

A well-built ADU incorporates modern insulation, efficient windows, and green materials that reduce environmental impact. Lower energy consumption translates into substantial savings and aligns with California’s sustainability goals. Professional craftsmanship ensures these features are properly installed for long-term performance, delivering both comfort and eco-conscious benefits.

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Advancing Modern Home Design with Trusted Local Expertise

In Ontario, California, and nearby areas, including Riverside, Fontana, San Bernardo, Norco, and Eastvale, ABL Contracting has been redefining home expansion through functional ADU construction for over five decades. We bring the perfect blend of architectural excellence, structural reliability, and local expertise to every project. Our mission is to help property owners unlock the full potential of their lots while supporting the growing need for affordable and flexible housing. With a proven reputation built over 50 years, ABL Contracting stands for integrity, craftsmanship, and innovation. From initial consultation to final inspection, every project is managed with precision and attention to detail. Our ADU solutions are not just structures—they’re thoughtfully designed living spaces built to endure, enrich, and elevate your property. Whether expanding for family, rental, or lifestyle purposes, we make your vision a lasting part of Ontario’s residential landscape.

Frequently Asked Questions

  • What is an ADU, and how can it benefit my property in Ontario, California?

    An ADU, or Accessory Dwelling Unit, is a secondary housing unit built on the same lot as your primary home. In Ontario, California, it increases property value, provides rental income potential, and creates more flexible living options for families or guests.

  • Does ABL Contracting handle all permits and approvals for ADU projects?

    Yes, ABL Contracting manages every aspect of the permitting and approval process. From zoning verification to building inspection coordination, our team ensures all paperwork and requirements are properly handled for full compliance with Ontario’s regulations.

  • Are ADUs legal in San Bernardino County, including Ontario?

    Yes, ADUs are fully legal throughout San Bernardino County, including Ontario, provided they meet state and local requirements. Homeowners must adhere to zoning, setback, and size restrictions, which professional contractors help navigate efficiently.

  • How long does it take to build an ADU in Ontario, California?

    The average ADU project timeline ranges from 4 to 8 months, depending on the size, complexity, and permitting speed. Factors such as design approval, utility connections, and material availability can affect the overall duration.

  • Can I convert my garage into an ADU without major reconstruction?

    In most cases, yes. A garage can be converted into a livable unit with proper insulation, plumbing, electrical, and HVAC integration. This is one of the fastest and most affordable ADU options available for homeowners.

  • Why should I choose ABL Contracting for my ADU project in Ontario, California?

    With over 50 years of experience, ABL Contracting provides expertise, transparency, and precision in every phase of ADU development. Our in-depth local knowledge of Ontario and neighboring communities ensures your project meets all regional standards and delivers lasting value.

  • How much does it typically cost to build an ADU in Ontario, California?

    ADU construction costs vary depending on size, design, and material choices. Generally, homeowners can expect a price range between $150,000 and $350,000. ABL Contracting offers detailed estimates to ensure budget clarity before construction begins.

  • Can ADUs be rented out legally in Ontario and surrounding areas like West Covina or Claremont?

    Yes, ADUs can be rented out legally for long-term tenants. Ontario and surrounding cities like West Covina and Claremont allow rental use of ADUs, provided they comply with city ordinances, safety codes, and proper permit documentation.

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