In this blog post, I walk you through the general requirements of building an ADU. You will learn where you can build an ADU, minimum and maximum sizes allowed, heights, and site considerations to be aware of.

The Comprehensive Guide to Building an ADU: Design & General Requirements

Introduction to Building an ADU

Are you thinking about building an ADU Accessory Dwelling Unit but don’t know what the ADU requirements are and how to go about obtaining an ADU building permit? If you own a single family or multi-family property, then you are eligible to build an ADU! Before we start, it’s essential to understand the ADU building regulations and its key requirements. 

What’s the Buzz on Building ADUs?

Homeowners, unleash the potential of your backyard with an Accessory Dwelling Unit (ADU)! These versatile secondary dwellings, also known as detached granny flats, backyard cottages, or tiny homes, offer a wealth of possibilities. These self-contained units have their own kitchen, bathroom, bedrooms and a private entrance.

Types of ADU Accessory Dwelling Unit

There are a 3 types of ADU’s that you can build are:

• Detached – conversion of an existing detached structure such as a garage or new construction
• Attached – conversion of an already existing space attached to the house or a new addition attached to the house
• Junior ADU – conversion of existing space, only applicable for single-family properties

If you want an in depth post about the types of ADU, check out my post here.

Essential ADU Building Requirements

Now, let’s get down to the nitty-gritty. Building an ADU comes with specific regulations that vary by location, so checking your local zoning codes is crucial. But here are some general requirements to keep in mind. 

I separated this section in 3 parts: General, Detached and Attached:

General ADU Building Requirements

Single-family and multi-family zoned lots in major cities welcome these versatile secondary dwellings. Each property can allow at least one ADU of at least 800 square feet, opening doors to additional living space, rental income, or creative home solutions.

Double check with your local municipality as each city can impose restrictions based on Public Utilities availability like sewer and water, and if you’re located in a Very High Fire Hazard Severity Zone.

They cannot be in the front yard or built in front of the main dwelling unit (only exception being if you’re converting an attached garage that faces the street). 

Quantity

This one varies by cities, but at a minimum one detached ADU and one attached JADU in single family properties. Or one attached ADU in Single family properties.

In multi-family properties, you can build at least 1 and up to 2 detached ADUs and 1 attached ADU. If you have more units, you can construct 25% of the number of units you have or the greater of the two. For instance, an 8-unit apartment permits the construction of up to 2 attached ADUs.

ADU Floor Plan Design & Amenities

An ADU Unit is an independent and separate living unit. It means it has its own kitchen and bathroom separate from the main house. The kitchen must have a stove, refrigerator and a sink and be fully operational.

My clients ask me if they can skip the stove in the kitchen because they plan to use the ADU as their office or studio, and don’t want to spend money on it. The short answer is NO, you need a stove.

No minimum bedrooms for your ADU! Cities typically focus on maximums bedroom count based on size, meaning you’re free to explore flexible layouts. Craft a multi-functional space with a sleeping nook, a dedicated home office, or even a hobby room – the possibilities are endless!

If you attached the ADU to the house, the design and style should be similar to the existing house.

ADU Parking Requirements

There are no parking requirements for ADUs, unless you’re in a Very High Fire Hazard Severity Zone. And even if you’re in a VHFHSZ, there are certain exceptions that you can include in the ADU design and proposal. Some exceptions include: limit your ADU to 800 square feet, detach it from the main dwelling unit, your property is ½ miles from public transit, etc.

There is no replacement parking for the main house or ADU when you convert the garage or carport! Keeping your garage is mandatory if you decide not to convert it into an ADU.

Parking requirements can vary by local municipality, so stay informed! In some situations, you might need to dedicate one covered or uncovered off-street parking space (think driveway) for your main dwelling. Check your local regulations to avoid any surprises! However, you cannot count the first 20-feet of your driveway (the front of the property) as parking space to meet this requirement.

Living within a ½ mile public transit zone unlocks a secret weapon: you don’t need to dedicate a space for your car! Let buses, trains, or carpooling handle the commute and enjoy the extra space at home.

ADU Owner Occupancy

Previously, the legal owner of the property had to occupy either the ADU or the main house. This requirement lifted in 2020. However, in 2025 this requirement might come into effect, we’ll wait and see if they extend the lift. 

JADU owners have to live either in the JADU or in the main house. Some cities require a signed, notarized and recorded covenant and agreement.

Covenant Not to Sell the ADU Separate from the House

You cannot to sell the ADU separate from the house on the same property.

Lot Coverage and / or Residential Floor Area / Floor Area Ratio

This one is more of a technical zoning term, but very important to know! Some cities limit the physical coverage on your lot. For example, if your lot is 5,000 square feet, the city has a maximum lot coverage of 50%. That means you can only build 2,500 square feet of your lot combined (incl. House, ADU, garage, etc).

Similarly with Residential Floor Area or Floor Area Ratio requirements, most cities impose a maximum 30% – 45% RFA or FAR on single family properties. Second floors also count towards RFA / FAR.

These two requirements (if enforced) limit the size that you can build your ADU. Please consult with a design professional or your local Zoning or Planning Department.

Fire Safety

No need for fire sprinklers for the ADU if the existing house (attached or detached) does not have them. However, there are many exceptions and cases that you will require fire sprinklers for your ADU, including:

• Located in a Very High Fire Hazard Severity Zone
• New Construction
• Nearby water hydrant does not have enough pressure (request the Fire Flow Form from your water company)

Consult with a design professional, local building and fire department, and your water company / purveyor.

ADU Addresses, Utilities & Connections

For the most part, you will get a new address for the ADU (and sometimes the Junior ADU). You can then apply for separate utility metering such as water, electricity and gas. Usually, water is the most expensive to meter separately because the work involves working on the street and/or sidewalk.

It’s best if the ADU have its own sewer line separate from the house sewer line to prevent any backups! You can connect the ADU sewer line to the main “sewer lateral”, the part of the sewer line that goes from your house and directly to the street.

ADU Permitting

The last point that I’m going to touch on for this Essential Accessory Dwelling Unit General Requirement List is permitting. I will go more in depth in another post.

You need a permit for your ADU. At the minimum you will need these city department approvals:

• Zoning / Planning: this department regulates the design and site layout 
• Building: this department ensures that the ADU meets building codes and regulations, including any life and fire safety issues (ie smoke detectors, property sized windows in bedrooms, etc)
• Miscellaneous departments such as Fire Department, School District, Sanitation, Public Works etc. This will vary by city and type of ADU proposed.

As always, consult with your city officials or a professional.

Essential Detached ADU Requirements

ADU size

Detached ADU can range in size: the minimum size is 150 square feet and the maximum size is 1,200 square feet. This, of course, depends on your existing property layout and if it makes sense with the current space you have.

If you convert your garage or another structure into an ADU then the size is already existing. And you can also build additional square footage to your garage conversion ADU.

You can also add to the ADU garage conversion so the entire ADU is up to 1,200 square feet. The same goes for new construction ADU size of 1,200 square feet maximum.

Height

The maximum height varies depending on your zone, but usually is at least 25-feet tall. This allows for a two-story ADU. Check with your city because some cities have different zoning rules.

If you convert any existing structures into an ADU, the existing height applies. For new construction or addition, the max. height is 25-feet or whatever local jurisdiction allowance.

You can build two separate ADU (can also be attached to each other) in a multi-family property. If you’re within ½ from public transit, the maximum height is 18-feet with 2 extra feet to match the ADU roof pitch to the existing house.

Most of the time for two-story ADU you need to check with your electric company to ensure there is no overhead power line conflict.

Setbacks and Minimum Distances

Setbacks are minimum distance requirements from any structures on the property to the property line. In general, most structures require a 5-foot setback (distance) from the property line. BUT only 4-foot setbacks are required for ADU’s. This is massive because you gain 1-foot for your ADU!

If you convert a garage or other structure, the setback remains, even if your garage is really close to your property line!

For new construction or additions, you will need to provide a 4-foot setback all around the ADU.

The minimum distance from the ADU to other structures is at least 6-feet. I don’t recommend going any less unless you want to sacrifice any windows or openings of the ADU or house that faces each other.

Essential Attached ADU Requirements

ADU size

Attached ADU size is up to 1,200 square feet or 50% of the existing house square footage, whichever is LESS. For example, with a 1,200 square foot house, you can attach a 600 square foot ADU to the house.

If you convert your attached garage, the size is existing. If you convert part of your house into an ADU, the resulting house square footage should be larger than your ADU by half. For example, I split my 1,600 square foot house into a 480 square feet ADU and the remaining 1,120 square feet remained the house. The 480 square foot ADU is less than 50% of the resulting house size after the split.

Junior ADU size is up to 500 square feet of the existing house. No additions allowed except for 150 square feet to accommodate getting in and out of the JADU.

Height

The existing height of the structure you’re converting remains. You cannot propose a two-story attached ADU to the house unless the existing house also is two-stories (for the most part).

Setbacks and Minimum Distances

Minimum setbacks and distances remain the same.

Conclusion on Building an ADU

That was a lot of material that we covered and I hope this didn’t confuse you.

Embarking on the ADU Accessory dwelling unit journey is actually pretty simple and easy if you keep these essential requirements in mind. 

Streamlined success! 90% of properties have the green light for ADUs, making the approval, permitting, and construction process as easy as 1-2-3. Get building and unlock the potential of your property!

As always, I would love to hear from you if this was helpful. Please leave me a comment or write me an email, I respond to every inquiry. This was a post about The Comprehensive Guide to Building an ADU: Design & General Requirements.

If you’re ready to begin your journey, check out my services and send me an inquiry. 

For more ADU resources check your cities’ website. Here are very useful sites to check out in LA County and LA City.