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In need of some extra living space? Whether your aging parents are coming to live with you, you want to construct a separate home office for passive income, or you are looking to build a backyard retreat, you can make it happen with an ADU. In order to get started, however, you must first understand the rules of the Los Angeles ADU Ordinance.

What is an ADU?

ADU is short for “accessory dwelling unit.” These units are commonly referred to as granny flats, cottages, and in-law units, to name a few.

Let’s turn to the Los Angeles County Department of Regional Planning for a formal definition.

According to the department, “An ADU is a dwelling unit with a full kitchen and bathroom, which is an accessory use to a primary or main single family residence. The ADU can be used as a rental, but cannot be sold separately from the primary or main single family residence. The existing residence must be a legally established structure.”

That gives you some idea as to what is required to build an ADU. We’re going to go into this in extensive detail in this article. But first, it is helpful to know about the four different types of ADUs:

Attached ADU

If you are looking to “build an attachment” to your home, you are probably thinking about an attached ADU. As the name implies, it is an addition which is physically connected to your main residence. It can go on the first floor or an upper story of your house.

Garage Conversion

You can outfit your garage to serve as a full dwelling unit by adding a kitchen and bathroom.

Interior Conversion

This is like converting your garage, but instead, you convert an existing basement or attic in your main residence.

Detached ADU

This is a standalone structure which you build on your property that is not connected physically to your main dwelling. The term “granny flat” specifically refers to a detached ADU. It also can be called a “backyard cottage.” Backyard retreats, offices, and guest houses may fall into this category.

All of these types of ADUs are legal in Los Angeles County. Each type of ADU has its pros and cons and is ideal for different situations. You’ll need to consider what makes sense for your home and grounds, as well as how you want to use the ADU in order to pick the type that is right for your needs.

Can I Build an ADU on my Property in Los Angeles?

Whether or not you are eligible to build an ADU on your property in Los Angeles County depends on whether the project fits within the parameters of the Los Angeles ADU ordinance.

What is the Los Angeles ADU Ordinance?

The Los Angeles ADU Ordinance is a set of regulations by the Los Angeles County Department of Regional Planning. They explain the requirements to legally put an ADU on your property. Let’s go over the basic requirements now.

Basic ADU Zoning Information

According to the official regulations, ADUs are permitted on properties with the following zone codes: R-1, R-2, R-3, R-4, R-A, A-1 and A-2, “or another zone where a single-family residence (SFR) is allowed by right with a plot plan (ministerial review).”

How Large Does Your Lot Need to Be?

There are no restrictions on lot size. What is important is just that your lot is residential and has a single-family residence already present.

How Large or Small Can Your ADU Be?

The minimum size for an ADU in Los Angeles County is 150 square feet. The maximum size for an ADU is 1,200 square feet. But there is a caveat for attached ADUs.

An ADU that is attached to a single-family residence cannot be larger than half the size of that main structure.

So imagine that your existing home measures 2,200 square feet. 50% of that is 1,100 square feet. That means that if you built an attached ADU, its size would be capped at 1,100 square feet.

This rule does not apply to detached ADUs, however. So, if your home is 2,200 square feet, and you construct a detached ADU, it can measure up to 1,200 square feet without violating regulations.

How Many ADUs Can You Build?

You can only build a single ADU on your property. Furthermore, if one already exists when you purchase the lot, you cannot construct another.

What to Know About Setbacks

If you are building a new structure to serve as an ADU (not merely converting one which already exists), you will need 5’ setbacks.

What to Know About Fire Safety

If you are building in a Fire Hazard Severity Zone, you must make sure that you are constructing over 200 feet away from publicly dedicated open space. Furthermore, there must be two forms of paved highway access measuring a minimum of 24 feet in width, if it is a Very High Fire Hazard Severity Zone.

If you have fire sprinklers installed in your home, you also will need them in your ADU. If not, it is up to you whether to include them or not.

What Can an ADU Look Like?

Your ADU cannot clash with your main residence. It also cannot violate any neighborhood rules concerning appearance.

Do You Need to Live on the Property?

No, you do not. In fact, the main structure does not even have to be your primary residence. It could be a second home, vacation home or investment property.

Can You Rent Out Your ADU?

Yes, you can rent the ADU to tenants. You even can rent out the main building. Renting out both or either can help to offset ADU construction costs.

Rules Concerning Parking

Parking rules pertaining to ADUs are rather verbose. You do not need to put in parking for the ADU if any of the following are true:

• There is public transportation within half a mile.
• The property is not in a Very High Fire Hazard Severity Zone.
• Car share is available on the same block.
• The district is classified as “architecturally and historically significant.”
• If you are converting a garage, guest house or similar existing structure.
• Only on-street parking is available, but the person in the ADU cannot obtain a permit.

Remember, these do not all need to be true. Only one needs to apply.

If you must put in parking for the ADU:

• You need to include two covered parking spaces.
• The spaces must measure 8 ½ ft. x 18 ft and must include 26 feet of space in which to back out.
• Required front and corner side yards may not be used for parking.

Los Angeles ADU Review and Approval

Before you can get to work building your proposed ADU, you will need to submit a completed application. You can find a list of the required documents in the full Los Angeles ADU Ordinance, which you may read here.

How Much Does it Cost to Build an ADU in Los Angeles?

The cost to build an ADU can vary considerably. Usually, you can expect a price in excess of $80,000. But in some cases, an ADU could cost significantly less or more.

Here are some of the factors which can impact the cost of an ADU:

• The type of ADU you choose to build. A brand new attached or detached ADU may cost more than a conversion of an existing structure.

• The style of a structure can make it cost more or less. If, for instance, you are building a detached ADU and have opted for a metal building, a Quonset hut probably will cost you less than a rigid frame structure.

• The size of the ADU. The larger the structure will be, the more expensive it will be. That being said, as the size of a structure increases, the cost per square foot tends to drop.

• Both the type of materials and the quality of those materials can have a significant impact on the price. The cost of materials also can vary based on economic factors. That means that when you buy your materials may also influence the final price.

• Before you can even begin building, you may need to take steps to prepare the land and set up utilities. The type of foundation you build may also cause the ADU to vary in price.

• The costs relating to getting your structure reviewed and approved can also differ based on the factors above.

• You will need to figure out how you will approach the actual construction. Will you hire a contractor? Will you build the ADU yourself? Will you use some combination of professional labor and DIY work? This is a major cost consideration.


While the Los Angeles ADU Ordinance does set restrictions for the construction of ADUs, many LA homeowners should find that it is fully legal for them to build an ADU on their properties.

Plan as much as you can in advance both to make sure your project will fit within the regulations and to keep costs under control.

With the right preparation, an ADU can be a flexible and cost-effective solution for increasing your living space.


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