True Blue Remodeling

Building an ADU: Step-by-Step Guide from Planning to Completion


Building an Accessory Dwelling Unit (ADU) can significantly enhance your property’s functionality and value. An ADU, commonly referred to as a secondary house or granny flat, is a self-contained housing unit located on the same grounds as a single-family home. It provides a unique opportunity for homeowners to expand their living space without purchasing new property. This can be ideal for housing extended family or generating rental income.

Embarking on the construction of an ADU involves detailed planning and adherence to local building codes. From the initial feasibility study to the final touches, each step requires careful consideration to ensure the project is successful and compliant. This blog post outlines the essential stages of building an ADU, providing homeowners with a comprehensive guide to navigate this complex process. By understanding these key phases, you can approach your ADU project with confidence, ensuring it meets all necessary legal and quality standards.

Feasibility and Design

Feasibility Study

A feasibility study is the first crucial step in building an Accessory Dwelling Unit (ADU). It assesses whether your property meets the necessary conditions for construction. This includes checking for local zoning laws that may affect building permissions and space allocations. It’s also important to evaluate whether the topography of your land can support the structure you plan to build.

In addition to physical considerations, a feasibility study should involve a detailed financial analysis. This analysis will help you understand the budget required for the project, including costs related to materials, labor, and permits. Knowing these financial aspects upfront can prevent unexpected expenses from derailing your project later. Furthermore, conducting a feasibility study helps you gauge the potential return on investment, which is especially important if you plan to rent out the ADU. This preliminary step sets the foundation for a successful and efficient ADU construction process.

Finalizing Design

Finalizing the design of your Accessory Dwelling Unit (ADU) is a critical step that shapes the entire project. It requires thoughtful consideration of how the unit will fit within your property’s existing layout. This phase involves selecting the architectural style, interior layouts, and exterior finishes that align with your needs and preferences.

It is essential to factor in local zoning restrictions and property setbacks during the design process. These regulations often dictate the maximum size of the building, its placement, and sometimes even specific design elements like roofing materials or facade colors. Collaboration with a skilled architect or designer can help navigate these requirements effectively.

Moreover, the design should also consider practical elements like natural light, privacy, and access points. Proper planning in these areas enhances the functionality and livability of your ADU. Once the design meets both your expectations and local codes, detailed construction documents can be prepared. These documents are vital for obtaining necessary approvals and guiding the construction team.

Construction Documents

Preparing detailed construction documents is a pivotal phase in the ADU building process. These documents serve as the official blueprint for your project. They must include comprehensive architectural designs, engineering specifications, and exact measurements. It’s crucial that these plans conform to all local building codes and regulations to ensure approval by city officials.

These documents should clearly outline every aspect of the construction, from the foundation to the roof. This includes electrical layouts, plumbing schematics, and structural details. Having precise and thorough construction documents helps avoid delays during the permitting process. It also ensures that contractors can accurately estimate costs and timelines.

Professionals such as architects and engineers typically draft these documents. Their expertise guarantees that the plans are both practical for construction and compliant with all legal requirements. Once finalized, these documents become the guide for the entire construction process, ensuring your ADU is built to specification.

Permitting and Revisions

City Review

The city review phase is critical in the ADU construction process, as it involves getting approval from local authorities for your plans. This step ensures that your proposed ADU complies with all municipal codes, zoning laws, and building regulations. It typically starts by submitting the detailed construction documents you prepared earlier.

During the review, city planners and engineers examine your plans to ensure everything from structural integrity to environmental compliance is in order. They check for adherence to safety standards and whether the design aligns with community aesthetics. This scrutiny is essential to prevent future legal or safety issues.

It’s common for the city to request changes or provide feedback on your submission. This could involve modifying certain aspects of the design or clarifying details in the plans. Responsive and timely communication with the city officials during this phase can help expedite the process.

Once you address all comments and meet the required standards, the city will issue the permits needed to begin construction. Obtaining these permits is a major milestone, as it officially allows you to start building your ADU. This process can take several weeks to months, depending on the complexity of your project and the efficiency of your local government offices.

Addressing Revisions and Obtaining Permits

Addressing revisions and obtaining permits is a crucial stage in the process of building an Accessory Dwelling Unit (ADU). After the initial city review, it’s common to receive feedback requiring changes to your plans. This step ensures that your project adheres to all local building codes and regulations.

The revisions may involve adjusting structural designs, modifying utilities, or enhancing safety features. It’s important to approach these changes constructively and see them as improvements to your project’s compliance and functionality. Collaborating closely with architects and engineers during this phase can help streamline revisions.

Once you make the necessary modifications, resubmit the plans for a second review. This re-evaluation is typically faster, as the major issues would have been addressed in the first round of feedback. Prompt and accurate responses can significantly speed up this process.

After satisfying all the city’s requirements, you will receive the building permits. These permits are the green light to commence construction. Obtaining them marks a significant milestone, as it means your project complies with local laws and is safe to proceed. Now, you can move forward with building your ADU, starting with site preparation.


Site Preparation

Site preparation is the initial physical step in constructing your Accessory Dwelling Unit (ADU). This stage sets the foundation for a successful build. First, the site must be cleared of any debris, vegetation, or old structures that could hinder construction.

Next, the land is leveled and graded. This process ensures proper drainage and a stable base for the foundation. It’s essential to address any potential issues with the soil’s stability or composition at this point.

Utilities also need to be considered. Ensure that water, electricity, and sewage lines are appropriately routed to support the new structure. Once these steps are completed, the site is ready for the actual construction to begin, marking a significant progression in your ADU project.

Construction Process

The construction process of an Accessory Dwelling Unit (ADU) begins once the site is fully prepared. Initially, the foundation is laid, establishing a solid base for the structure. Following this, the framing stage occurs, where walls and roof structures are built, visually shaping the ADU.

Next, the installation of electrical, plumbing, and HVAC systems is carried out. These are critical for ensuring the ADU is functional and comfortable. After these systems are in place, insulation and drywall are added, followed by windows and doors to secure the building.

Exterior and interior finishes are then applied, which include siding, painting, and flooring. These finishes not only protect the building but also define its aesthetic appeal. This systematic approach ensures the construction of the ADU progresses smoothly and efficiently.

Compliance and Inspections

Compliance and inspections are integral to the construction of an Accessory Dwelling Unit (ADU). Throughout the building process, adherence to local building codes and regulations is essential. This ensures the safety and legality of the structure.

Inspections are conducted at various stages of construction. For example, there are inspections for the foundation, framing, electrical systems, and plumbing. These are performed by city inspectors who verify that each component meets the specified standards.

Passing these inspections is crucial for continuing with subsequent phases of construction. Any issues identified need to be corrected before proceeding. Final inspections are done once construction is complete, ensuring everything is up to code before the ADU can be occupied. This rigorous process guarantees the structural integrity and safety of the ADU.


Final Inspections

Final inspections are a decisive phase in completing your Accessory Dwelling Unit (ADU). These are conducted to ensure that all aspects of the construction meet local building and safety codes. During final inspections, every detail of the ADU is meticulously reviewed, from electrical systems and plumbing to overall structural integrity.

Inspectors will also verify that the finished construction matches the approved plans submitted during the permitting phase. If any discrepancies or issues are found, they must be resolved before any occupancy permits can be issued. Successfully passing the final inspections signifies that your ADU is compliant and safe for occupancy. This milestone is crucial as it allows you to legally rent out the space or have it occupied.

Finishing Touches

The finishing touches of your Accessory Dwelling Unit (ADU) bring your project to completion and personalize the space. This phase involves installing fixtures, such as lighting, hardware, and appliances, which are essential for functionality and aesthetics.

Interior painting and flooring are also completed during this stage, enhancing the visual appeal and comfort of the ADU. Additionally, exterior work such as landscaping and walkways not only improves curb appeal but also integrates the ADU with the main property.

Ensuring all elements are finished to a high standard is crucial for creating a welcoming and livable environment. These final steps transform the construction site into a beautiful and functional living space, ready for occupancy.


Building an Accessory Dwelling Unit (ADU) is a comprehensive process that requires meticulous planning, execution, and compliance with local regulations. From the initial feasibility study to the detailed design, permitting, and construction phases, each step is crucial for a successful outcome. The final inspections and finishing touches mark the culmination of your hard work and investment.

By understanding and navigating these steps effectively, you can ensure that your ADU project not only meets all legal requirements but also enhances your property’s value and functionality. An ADU provides flexible options for additional living space or rental income, making it a valuable addition to your property. With careful planning and execution, your new ADU will be a source of pride and utility.