Second-Story ADU Additions

We help you expand your living space with our premium second-story ADU addition services at Modern ADU Builder. Adding a thoughtfully designed second story to your home is a practical and innovative way to create substantial additional room without sacrificing any of your valuable yard or outdoor living areas.


Many families throughout the region find this versatile solution perfect for accommodating growing households, generating extra rental income, or creating a comfortable, private space for guests, aging parents, or adult children returning home. Our second-story ADUs transform underutilized vertical space into functional, beautiful living environments that enhance both your lifestyle and property value.


With our comprehensive knowledge of local zoning regulations, permit requirements, and our unwavering commitment to quality construction practices, we work diligently to ensure your second-story ADU perfectly complements your existing property while meeting your unique needs and aesthetic preferences.

Design and Planning Process for Second-Story ADUs

Personalized Design Consultation

Our process begins with a conversation to understand your goals, budget, and property needs. We schedule meetings where you can share your ideas, ask questions, and discuss specific priorities.



Key topics include space use, who will live in the ADU, and special requirements such as accessibility or privacy. We use this information to shape design suggestions that fit your home style and preferences.


Open communication allows for real-time feedback and adjustments. We answer any questions you have, suggest practical solutions, and keep you informed. Your input guides each step so the final plan matches your vision for the project.

Custom Architectural Solutions

We create floor plans and exterior designs tailored for your property. Our architectural team prepares multiple layout options to make the best use of your available space without sacrificing comfort or style.


We factor in height limits, stair placement, and the impact on your main house. Attention to detail ensures features like windows, balconies, and private entrances work for your daily life.



We review key design choices together, using sketches and 3D models when helpful. This approach lets us solve potential challenges early and keep quality at the center of our work.

Navigating Local Zoning Regulations

Building a second-story ADU comes with strict rules about size, height, setbacks, and parking. We research current city codes and reach out to local building departments for clarity on any requirements.


Our team prepares the needed paperwork and submits plans for city review. We handle communication with city officials to address requests for changes or extra information.



We track progress and update you at each stage. Our goal is to help you avoid permit delays, stay in compliance, and achieve faster project approval, making the process as smooth as possible.

Factors Influencing Project Costs

Several main factors affect the cost of a second-story ADU. One of the largest costs is size, since building cost per square foot usually ranges from $150 to $300. The bigger your addition, the higher the price. For a typical unit, total construction costs can land between $100,000 and $350,000 or more.


Site conditions play a major role. Adding a story means reinforcing or upgrading your existing structure. Costs go up if your current home needs extra work to support the addition. Local building codes and permit fees will also add to the price.


Special design features, like custom finishes, energy-efficient systems, or unique layouts, can raise the budget. Utility connections—plumbing, electricity, and HVAC—often cost more for second-story builds than attached or garage conversions. We guide you through each decision to match your vision and your budget.

Green Building Materials

We use modern, eco-friendly materials that are built to last. For framing and siding, we choose options like engineered wood, recycled steel, and fiber cement. These materials limit waste and are often made with recycled content.


For insulation, we prefer products with high R-values such as cellulose or spray foam, which help keep indoor temperatures steady. We use low-VOC paints and finishes that protect indoor air quality for you and your family.



We also consider sustainable flooring like bamboo and recycled-content tile. Using durable building materials means fewer repairs and replacements, resulting in less environmental impact and cost to you over time.

Energy-Saving Features

We design every second-story ADU addition to help you save energy year-round. High-performance windows with double or triple panes help reduce heat loss during winter and block heat during summer. LED lighting uses far less electricity than traditional bulbs and lasts much longer. Smart thermostats let you program heating and cooling schedules, saving energy even when no one is home.


Whenever possible, we recommend solar panel installation to help offset your electricity use. We seal gaps around doors and windows to prevent drafts, which keeps your ADU comfortable while reducing heating and cooling costs.



Other features may include high-efficiency HVAC systems, Energy Star appliances, and low-flow water fixtures to reduce resource use. These choices not only protect the environment but also offer you real savings on monthly utility bills.

FAQs on Second-Story ADU Additions

Hi there! Have some questions about our service? Find the answers below. 

  • What are the zoning requirements for constructing a second-story ADU in San Diego?

    In San Diego, second-story ADUs must follow city zoning codes, which set rules about lot size, height, and setbacks from property lines. We need to check if your property meets all local rules, including limits on ADU size and parking requirements. Permits are always required. Homeowners Associations (HOAs) may also have restrictions. It’s important we review your address and local guidelines before moving forward.

  • How much does it typically cost to add a second-story ADU to an existing property?

    Adding a second-story ADU in San Diego can cost between $200,000 and $400,000 or more, depending on size, design, and finishes. The price is higher than ground-level ADUs due to additional engineering needs and structural upgrades. Permitting, design, utility changes, and labor are included in the total costs. We provide detailed quotes after assessing your home and project goals.

  • Can you recommend reputable builders specializing in second-story ADU constructions?

    Modern ADU Builder specializes in designing and building second-story ADUs. We have experience with both custom builds and prefab units, and we fully handle permits, design, and construction. For other builders, we suggest choosing licensed contractors with experience in multi-story ADUs in San Diego. Always check reviews, references, and completed projects before hiring.

  • What are the advantages of choosing a prefab ADU for a second-story addition?

    Prefab ADUs can reduce construction time and limit disruption to your daily life. They’re built in a factory, inspected, and then delivered to your property for assembly. Prefab units may lower some costs compared to fully custom builds, and the quality is consistent. Not all properties fit prefab options, so we check for compatibility during the planning phase.

  • How long does the construction process for a second-story ADU typically take?

    Describe the item or answer the question so that site visitors who are interested get more information. You can Building a second-story ADU from start to finish usually takes 8 to 12 months. This timeline includes design, permitting, and actual construction. Delays can happen if permits take longer, or if your existing home needs extra structural work. We keep you updated throughout every step to avoid surprises. this text with bullets, italics or bold, and add links.

  • What are the most efficient floor plans for maximizing space in a second-story ADU?

    Open-concept layouts, combining kitchen and living areas, help create more usable space. Including large windows and built-in storage makes small areas feel bigger. Placing bedrooms and bathrooms along the edges provides privacy and maximizes natural light. We work with you to personalize the plan while keeping the layout practical and comfortable.