ADU Requirements: A Step-by-Step Guide

ADU requirements include various regulations and guidelines that dictate how homeowners can build and use an accessory dwelling unit (ADU) on their properties. These requirements vary quite a bit depending on where you live, so if you’re a property owner looking to add an ADU, it’s super important to first know the specific guidelines for your state, county, and city.

This article will explain the basic steps required to meet the various ADU requirements. You’ll learn about zoning laws that affect where you can build, what permits you’ll need, size limits for your ADU, and more. By the end, you’ll have a good grasp of everything you need to bring your ADU project from idea to reality.

What Is an ADU?

An ADU, or accessory dwelling unit, is a secondary living space on your property that can be used for various purposes, including a rental unit, home office, or guest house. It’s typically smaller than your main residence and can be attached to the main house or a separate structure.

ADU Types

ADUs come in a few different types, each with their own unique features:

• Detached ADUs are separate buildings on your property, often used as a rental unit or guest house. These standalone units give you maximum privacy and flexibility in how you use them.
• Attached ADUs are connected to the main house, so they add extra living space while blending nicely with your primary residence. They can be built above a garage, as a wing of the house, or designed to fit right into your main home.
• Interior ADUs are a great option for homeowners looking to make the most of their current space without adding on to the outside. These types of ADUs convert existing areas like garages, basements, or attics into livable units.
• Junior ADUs (JADUs) are a specific type of interior ADU that’s smaller in size. They’re perfect for in-law suites or home offices.

The type of ADU that works best for your property depends on factors like the available space on your property, local regulations, and what you plan to use the unit for.

Number of ADUs Permitted on One Lot

One of the first questions homeowners ask when considering an ADU is, “How many ADUs can I build on my property?” The answer depends largely on where you live because local regulations can vary a lot from state to state.

Here’s a look at two examples:

In California, recent changes in the law have made it a lot easier to add ADUs. Generally, you can have one full-sized ADU plus one junior ADU (which is a bit smaller) on your property. This means you could potentially have two extra units on your property in addition to your main house as long as they meet specific size and zoning requirements.

In states like Oregon, the standard is usually one ADU per single-family home, at least in most urban areas. However, some cities have relaxed regulations to encourage homeowners to build more ADUs. In such places, you can have multiple ADUs on a single lot under certain conditions, especially in more rural parts of the state.

Regardless of where you live, it’s important to check with your local zoning office to understand specific rules for your area. Factors such as the size of your lot, the zoning designation, and any neighborhood restrictions can all impact how many ADUs you’re allowed to build.

Basic ADU Requirements

When planning your accessory dwelling unit, there are a few basic requirements you’ll need to meet:

• Must Function as an Independent Living Unit: Your ADU needs to be a complete, self-sufficient living space without relying on the main house. This means it should have its own kitchen, sleeping area, and bathroom. However, depending on where you live, a JADU may not necessarily have a separate bathroom.
• Utility Connections (Water, Sewer, and Electrical Hookups): You’ll need proper connections for water, sewer, and electricity. These hookups have to follow local building codes to make sure everything runs safely and smoothly.
• Impact on Existing Utility Systems: Adding an ADU can affect your current utility systems. It’s important to check if your existing setup can handle the extra load or if you’ll need some upgrades. Keep the following basics in mind:
  • Make sure the ADU’s water supply doesn’t lower the water pressure in the main house.
  • Confirm that the ADU’s sewer connection doesn’t overload the existing sewer system.
  • Ensure that the new unit’s electrical load doesn’t exceed the capacity of your main house’s electrical system.

Zoning Laws for ADUs

Zoning laws are important when it comes to building an ADU. These local regulations essentially dictate what you can and can’t do with your property, including things like the size, placement, and number of ADUs allowed.

Permitted ADU Types

The types of ADUs that are allowed can vary by location. Some areas may only permit certain configurations, such as detached units or conversions of existing spaces.

For example, prior to recent changes in California law, the city of San José did not allow Junior ADUs (JADUs). However, the new state regulations now require San José to permit JADUs, which can be up to 500 square feet in size.

Lot Size and ADU Size

Local zoning codes often set minimum lot sizes and limits on how many buildings you can have. Smaller properties may have more restrictions. For instance, the minimum lot size for an ADU in San Jose is 3,000 square feet before recent changes in California law.

While there is currently no statewide minimum lot size to build an ADU in California, the maximum size is 1,200 square feet for a detached unit. Attached ADUs can be up to 50% of the primary residence’s size.

Setbacks and Height

Zoning rules determine how close the ADU can be to your property lines, as well as height limits. These can really shape the physical design. For example, in some California cities, detached ADUs must be at least 6 feet from the main house and not be taller than 16 feet. There should also be a minimum of four feet setback from any property lines (or 10 feet if the ADU is more than 800 square feet).

Research Zoning for Your Property

You’ll need to do some research to determine your property’s zoning rules. Start by contacting your city or county planning department; they can provide the current zoning code and ADU regulations.

Be sure to review the details of special district rules that could apply to your property. You may also want to consult with a local land use expert or architect who knows the ropes in your area.

Permits and Approvals

Before you can start construction on your ADU, you’ll need to obtain the proper permits and approvals from your local government. This process can vary depending on your location, but here are some of the common permits you’ll need:

• Building Permit: This covers the construction of the physical structure and makes sure the unit meets all building code requirements.
• Electrical Permit: You’ll need this for installing the ADU’s electrical system.
• Plumbing Permit: This is required for the water, sewer, and drainage systems.
• Zoning Permit: This permit confirms that your ADU complies with local zoning regulations.

In some cases, you may also need additional permits, such as a grading permit, if your site requires significant prep work before construction.

Occupancy and Usage Restrictions

Another important requirement to keep in mind when building an ADU is the rule about who can live in it and how it can be used.

Who Can Live in the ADU?

As usual, occupancy rules regarding ADUs are not universal, but common requirements include:

• Owner Occupancy: In some states like Utah, the rules require you, the property owner, to live in either the main house or the ADU. This stops people from just renting out the ADU if the owner doesn’t actually live there.
• Relation to Owner: Some places also restrict who can live in the ADU. For example, they might only allow family members or caregivers of the property owner.
• Minimum Age: A few cities, such as Fairfax in Virginia, have age restrictions. For example, they may require the ADU occupant to be at least 55 years old.

Short-Term Rental Regulations

The rise of short-term rental platforms like Airbnb has made a lot of cities put rules in place around using ADUs for this kind of renting:

• Prohibited: Some places completely ban short-term rentals in ADUs. If you live in such places, you have to rent out your ADU for at least 30 days at a time.
• Restricted: Other cities limit the number of days per year you can rent an ADU short-term to no more than 90 days.
• Allowed: A few places allow short-term rentals in ADUs without any restrictions, but that’s not very common.

Design and Aesthetic Guidelines

Many areas have specific regulations about the architectural style of ADUs. Common requirements include:

• The ADU must be compatible with the style of the primary dwelling. For example, if the main house is a traditional craftsman, the ADU should have a similar aesthetic.
• Detached ADUs should still visually connect to the main house through matching architectural details, such as roof styles, siding materials, and colors.
• The ADU should blend in with the overall neighborhood character and not stand out as a separate structure.

Materials and Design Consistency

To ensure ADUs have a cohesive look with the main house, local regulations usually require homeowners to:

• Use the same siding, roofing, and trim on the ADU as the main house.
• Match the windows, doors, and decorative touches.
• Paint or stain the ADU in the same colors as the main house.
• Make sure the size and shape of the ADU fit with the main house.

Financing Your ADU Project

Building an ADU can be a bit expensive, especially if you’re putting up a detached unit. It’s common for homeowners to refinance their mortgage, take out a renovation loan, or use their personal savings.

Another financing solution is to consider a RenoFi Home Equity Line of Credit (HELOC). This unique option lets you tap into your home’s equity and access several times more than a traditional HELOC would provide.

Mastering ADU Requirements for a Successful Project

Before you start building, it’s important to know the specific ADU requirements in your area. Following local zoning laws, building codes, and permit processes can save you a lot of frustration, including costly delays and fines. In some cases, not following these rules could mean having to tear down your new addition.

To ensure a smooth and successful ADU project, it’s essential to work closely with experienced professionals, such as architects, contractors, and local officials. They can guide you through all the ADU regulations, help you get the right permits, and give you insider tips to avoid any headaches.

If you’re a homeowner looking to finance your ADU project, RenoFi, a licensed mortgage broker, is here to help.