Before You Build
ADUs are an exciting way to maximize your property’s potential, but they come with regulations that vary by state, city, and even neighborhood.
Before you break ground for your new ADU, it's crucial to know the ground rules.
You're in the right place if you're asking, “Do I need a permit to build an ADU? What are the zoning laws for ADUs? What are ADU foundation requirements?”
ADUs are an exciting way to maximize your property’s potential, but they come with regulations that vary by state, city, and even neighborhood. Some areas encourage ADU development, while others have strict limits on size, placement, or whether you can rent them out.
In this guide, we’ll break down:
By the end, you will have a clear roadmap to navigate the legal and practical steps of building your ADU with no surprises!
Building an ADU is an exciting project, but before you get too far into planning, there is one crucial step: securing the right permits. Whether you're converting a garage, adding a backyard cottage, or attaching a new unit to your existing structure, local building authorities will require permits to ensure the structure is safe, legal, and compliant with zoning codes.
Permits ensure your ADU is safe, up to code, and compliant with local laws. Skipping them can result in fines, stop-work orders, legal issues when selling your home, or costly safety hazards. Taking the time to get proper approvals upfront saves time, money, and stress in the long run.
The permits required for your ADU depend on your location and project scope. The most common include:
Each permit may involve inspections at different construction phases to ensure compliance with safety codes.
Getting an ADU permit involves several steps that vary by city and county. While the process can seem complex, breaking it down makes it more manageable:
Before applying for a permit, review your city’s ADU zoning laws and building codes. Some areas have strict size limits, setback requirements, or parking rules that could impact your design.
You will need detailed architectural drawings of your ADU that outline the structure, electrical layout, plumbing system, and foundation details. Many homeowners work with an architect, contractor, or ADU specialist to ensure their plans meet local requirements.
Submit your application to your local building department or planning office, including:
Once approved, inspections will be required at key construction stages: foundation, framing, electrical, plumbing, and final safety checks. After passing all inspections, the city will issue a Certificate of Occupancy, making your ADU officially legal and move-in ready.
Approval timelines vary based on city regulations, workload, and special approvals. While most permits take a few weeks to several months, delays can occur due to zoning variances, high application volume, or incomplete paperwork.
Costs vary widely based on location, ADU size, and project scope. On average, homeowners can expect to pay between $3,000 and $10,000 in fees, including:
Yes, if you're in Cincinnati, Ohio, you will need a building permit, zoning approval, and utility connections. Cincinnati has recently updated its laws to encourage more ADUs, but there are still specific regulations on lot size, height limits, and occupancy requirements.
Homeowners should check with the Cincinnati Department of Buildings and Inspections to get the most up-to-date requirements. Casita can also help guide you through the local process for a smooth experience.
Zoning laws determine where and how you can build an ADU, including lot size, setbacks, height limits, and rental use. Understanding these regulations before you start will help you avoid costly delays or design changes.
One of the first things to check is whether your lot qualifies for an ADU. Some cities require a minimum lot size, and if your property is too small, you may need to apply for a variance (a city-approved exception).
Setback regulations dictate how close an ADU can be to property lines and other structures. Common setback requirements include:
ADU size limits vary, but many cities cap detached ADUs at 800–1,200 sq. ft. and restrict attached ADUs to 40–50% of the size of the primary residence.
In Cincinnati and many surrounding areas, you can build a separate structure up to 800 sq. ft. and under 13 ft. in height without zoning or building permits. Larger ADUs are still possible but will require permitting and zoning approvals.
Some cities require the homeowner to live on the property (either in the main house or the ADU), while others allow both to be rented separately. Special permits may be required if you plan to use your ADU as a short-term rental (e.g., Airbnb).
Yes, but only in certain residential zones. Some areas allow detached ADUs, while others limit ADUs to attached or internal conversions (such as a basement or garage apartment).
Cincinnati does not require owner-occupancy, meaning both the main home and ADU can be rented out separately. However, short-term rentals may have additional restrictions.
Zoning laws change over time, so always verify the most up-to-date regulations before starting your ADU project.
ADU Foundation Requirements
ADUs need to be structurally sound and up to code. Two key components of any ADU construction are foundation stability and electrical safety. These requirements vary depending on the type of ADU, the local climate, and zoning regulations, but they all ensure that your unit is safe, durable, and legally compliant.
The foundation of an ADU depends on the type of structure and the condition of the land. A solid foundation provides stability, prevents shifting, and supports the weight of the ADU over time. There are three main types of foundations used for ADUs:
A slab-on-grade foundation is one of the most common choices for ADUs. It consists of a concrete slab poured directly onto the ground, providing a sturdy, low-maintenance base. This type of foundation works well for flat lots with stable soil and is often more affordable than other options. However, it may not be ideal for colder climates where frost heave can cause cracks in the concrete.
A crawl space foundation raises the ADU above the ground, creating a small space underneath for plumbing, electrical wiring, and ventilation. This is a great option if your lot has uneven terrain or if you want easier access to utility lines. Crawl space foundations provide better insulation than slab foundations, making them a popular choice in areas with extreme temperatures.
For homeowners looking to maximize space, a basement foundation allows for extra storage or even additional living space below the ADU. This is a more complex and costly option but can increase property value and provide better insulation. However, it requires extensive excavation and may not be feasible on all lots.
Cincinnati’s climate, with cold winters and freeze-thaw cycles, makes frost-proof foundations especially important. Local building codes require foundations to be at least 30 inches deep to prevent frost damage. If you’re planning an ADU in Cincinnati, working with a builder familiar with local soil conditions and drainage requirements is key to ensuring long-term durability.
Once you understand the zoning laws, permits, and building requirements, the next step is turning your ADU from an idea into reality. Proper planning ensures a smooth, stress-free process while avoiding costly mistakes. Whether you're building a rental unit, a guest house, or a home office, taking the right steps from the beginning will save time and money.
Every successful ADU project starts with a clear plan. Before construction begins, you’ll need to consider the design, budget, and logistics of your new space.
Start by asking: What's the goal of your ADU? Your intended use will influence the design and cost. ADUs can serve as:
Once you determine the purpose, set a realistic budget given your resources. Costs will depend on size, materials, permits, and labor. On average, ADUs range from $100,000 to $300,000, but working with an experienced builder can help keep costs manageable.
ADUs come in different forms, including detached backyard units, garage conversions, and basement apartments. Each option has unique benefits and potential challenges.
If you’re unsure which type best suits your property, a design consultation with an ADU specialist can help you balance function, cost, and aesthetics.
Even if your ADU meets size and setback rules, you’ll still need to apply for permits before construction. Start by confirming requirements with your local building department.
For Cincinnati homeowners, this means:
Some homeowners choose to work with a builder who can handle permitting and approvals, simplifying the process.
Choosing the right builder is one of the most important decisions in your ADU project. Look for professionals who have experience with ADUs and local zoning laws, a strong portfolio of past projects, and clear contracts, timelines, and budget expectations.
Casita specializes in custom ADU construction and helps homeowners navigate everything from design and permitting to final construction.
Finding the Right ADU Builder
Not all contractors are experienced in ADU-specific construction, which requires knowledge of small-space design, zoning laws, and multi-use functionality. When hiring a builder, ask:
Casita offers expert ADU planning, design, and construction, ensuring every project is completed on time and within budget. Our team handles the entire process, so you don’t have to navigate zoning laws and permits alone.
A Future ADU Starts with Local Regulations
An ADU is a smart, flexible investment that can add value to your home, create rental income, or provide extra living space. However, success depends on understanding ADU requirements in your area and careful planning with the right professionals.
If you’re a property owner considering an ADU or junior ADU in Cincinnati, Casita can help. Our team makes the process simple, handling everything from zoning research to construction so you can focus on enjoying your new space.
Ready to get started? Contact Casita today for a free consultation, and let’s bring your ADU vision to life.
