The cost to build a 400-square-foot ADU, such as the Fir one-bedroom design, typically ranges between $150,000 and $220,000, depending on site conditions, building materials, and design complexity. This cost includes factors like architectural plans, building permit fees, utility hookups, and full-sized appliances. As a cost-effective way to add a private retreat, guest house, or housing for family members, the Fir balances efficient space with ample living space, making it an excellent choice for San Diego homeowners. This Accessory Dwelling Unit (ADU) offers everything needed for independent living while maximizing future home valuation through thoughtful design and expert construction.

In San Diego County, 400-square-foot ADUs must follow specific zoning laws and building codes. The building department requires that detached ADUs maintain a minimum 4-foot setback from property lines per California’s zoning requirements. While no parking is required for units near public transit, all ADU projects must comply with applicable code requirements, including a basic kitchen, bathroom, and efficient Water Heater placement. Detached Accessory Dwelling Units up to 750 square feet are exempt from impact fees, making compact ADUs like the Fir a more affordable option. Our team ensures every project is designed to meet both city planning standards and your personal vision for additional living space.

Absolutely. The Fir is a 400-square-foot, one-bedroom ADU design that proves compact layouts can still deliver comfortable living space with a perfect balance of form and function. With a spacious bedroom, full bathroom, L-shaped kitchen, and open living area, the Fir utilizes efficient design elements and smart storage solutions to make every square foot count. Whether used as a cozy guest house, a granny flat, or additional housing for family members, this plan offers adequate living space for day-to-day comfort. Ideal for San Diego’s residential properties, the Fir serves as a secondary living space or long-term rental while aligning with the city’s accessory dwelling unit designs and urban development goals.

Yes—absolutely! The Fir is a 400-square-foot, one-bedroom design built on a strong foundation of smart design and efficient layout, but it's also highly flexible. Whether you're looking to convert it into a cozy law suite, add accessibility features like a curbless shower, or optimize the L-shaped layout for a dining nook or Formal Dining Room3, our customization options make it possible. We offer a range of custom ADU designs and semi-custom plans to align with your needs, whether that’s more built-in storage, a different design aesthetic, or special cabinetry for storage. From creative design elements to detailed floor plan designs, our goal is to match the Fir to your lifestyle, your primary residence, and your long-term vision.

Definitely. The Fir ADU is a compact, cost-effective way to create a secondary living space that’s ideal for long-term tenants, short-term rentals, or even housing for family members. Its private entrance, full functional kitchen, bathroom with shower, and in-unit laundry make it completely self-contained—perfect for generating additional income or helping offset the mortgage on your primary residence. This attractive option also complies with parking requirements and fits seamlessly into existing or proposed single-family home lots. Many San Diego homeowners turn to the Fir as a practical solution that blends expert craftsmanship with real project value and backyard potential.

Most 400-square-foot studio or one-bedroom ADUs like the Fir take about 4 to 6 months from design to completion, depending on permitting timelines, zoning regulations, and site conditions. Our streamlined approach reduces unnecessary delays and keeps your ADU construction on track, even in areas with more complex coverage regulations or building dimensions. With a clear process built on years of experience in ADU house plans & construction, we help you navigate every phase—from comprehensive design to build-ready plans—with clarity. Whether you’re considering build-ready and semi-custom options, evaluating cost factors, or exploring financing options, the Fir is an efficient choice designed to move from concept to reality without sacrificing quality.

Yes, the Fir is an excellent choice for multi-generational living, especially for aging parents, in-laws, or adult children who need a cozier living space with privacy and independence. As a 400-square-foot layout, the Fir balances functionality and comfort within a compact ADU size, offering a bedroom layout and private bathroom that work well as law suites or Carriage houses. While larger units like 1,000-square-foot or 1,200-square-foot designs may offer additional bedrooms, the Fir's balanced layout and open-concept living spaces make it ideal for backyard placements near the primary residence, maintaining proximity while fostering autonomy. With smart use of vertical space, built-in storage, and thoughtful planning, this ADU supports family-first living without sacrificing comfort.

Absolutely. Adding an ADU like the Fir is a proven way to increase future home valuation, offering both additional housing options and flexible functionality. As the demand for compact studios, backyard cottages, and flexible ADU sizes grows, more buyers are seeing value in homes that offer rental income potential, private guest spaces, or additional space for family. The Fir’s smart use of design plans, built-in storage solutions, and its open-concept layout contributes to a more desirable property with beautifully designed and functional living areas. Unlike average homes, a property with an ADU—especially one as efficient and well-executed as the Fir—stands out in today’s market, often commanding a higher resale price.

Yes, the Fir’s compact ~16' × 25' footprint is a perfect fit for a standard garage conversion. This 400-square-foot layout works seamlessly for homeowners looking to transform underused garages into fully functional ADU house plans with a compact kitchen, full bath, and private bedroom. The Fir fits within the guidelines of California’s 4-foot requirement for setbacks and is especially popular in cities with strong city planner support for infill housing like Crescent City. Garage conversions are a smart and cost-effective way to add livable square footage while saving on construction materials and reducing building costs. Whether you're envisioning a cozy guest suite, a Golf Cart accessible retreat, or an income-generating rental unit, the Fir brings your garage to life as a modern, compact, and value-boosting living space.

Custom ADU plans like the Fir offer unmatched design flexibility and are tailored specifically to your property, lifestyle, and vision. Unlike pre-approved layouts, which may not fully utilize your lot’s dimensions or comply with unique zoning rules, a custom plan ensures optimal use of your space—whether it’s a 440-square-foot layout that balances privacy or a 750-square-foot layout with a dedicated dining area. With a custom design, you avoid dead space, add efficient storage, and choose from a broad array of designs, color options, and architectural styles. While custom plans may involve slightly higher amounts on design fees, the result is a more beautifully spaced, open-concept living space that adds long-term value to your home. It’s the difference between a one-size-fits-all template and a truly personalized concept space backed by ADU experts.

The most affordable ADU option is typically a compact size unit like a 360-square-foot studio ADU or 400-square-foot layout with basic finishes and simplified construction. Smaller designs such as a 450-square-foot layout or 500-square-foot design reduce construction details, material costs, and often qualify for fee waivers under California's 4-foot requirement regulations. These cost-saving units often feature basic appliances, efficient layouts, and clever built-in storage solutions. While larger, more elaborate models like 1,000-square-foot designs or 1,192-square-foot layouts offer expansive living space, smaller ADUs provide a more cost-effective, streamlined path to additional living space, especially for those with tighter budgets or existing multi-family buildings looking to add rentable units with minimal overhead.

A typical 1-bedroom ADU ranges anywhere from 400 to 800 square feet, depending on layout and design preferences. The Fir, for example, is a compact 400-square-foot layout with a smart bedroom-bathroom house configuration that balances efficiency and privacy. Other popular 1-bedroom ADU sizes include the 500-square-foot design, 550-square-foot design, and 648-square-foot design, each offering unique combinations of open-concept living spaces, eat-in kitchen islands, and ample storage. Whether you're drawn to a cozier space or a more expansive layout, there’s a wide range of ADU house sizes to fit your goals—perfect for maximizing value and functionality in a beautifully spaced secondary unit.

In California, the smallest Accessory Dwelling Unit (ADU) allowed by code is 150 square feet, which is typically reserved for compact studios or efficiency units. However, most house providers and design firms recommend starting at around 360 to 400 square feet to create beautifully spaced, open-concept living spaces that offer essential comfort and functionality. A 440-square-foot layout balances privacy with livability, especially when designed with ample light, smart construction blueprint symbols, and thoughtful construction processes in mind. These compact ADUs are ideal for homeowners working with tight space constraints or narrow basis of backyard access, and they’re a smart way to enter the building industry without the complexity of more extensive construction seen in 1-2 bedroom or 800-square-foot and 824-square-foot layouts.

Whether it’s more affordable to build an ADU or add onto your primary residence depends on several critical factors—including construction processes, property layout, and desired functionality. A home addition might seem cost-effective upfront, but it can often trigger extensive construction that impacts your existing structure and utilities. In contrast, a well-planned compact ADU—like a 624-square-foot layout or 623-square-foot design—can be built as a detached structure with fewer structural disruptions and clearer construction project hinges. ADUs also offer greater flexibility, from additional storage and rental income to future resale benefits, making them more than just added square footage. Plus, they give you more freedom in design—from a balance of style to features like an eat-in kitchen island or concrete pendant lights—and often feel cooler than larger homes in terms of creative layout and blend of space efficiency. For many homeowners, ADUs represent a smarter investment in today’s fast-evolving city to city housing market.