The Full Building Cost Guide: ADU, Addition & Garage Conversion

As the new California state’s housing laws have paved the way for increased development of ADUs specially after AB 1033 and SB 1211 passes to allow homeowners to sell the ADU separately in order to cope with the crises of affordable housing more homeowners who are eligible to build an ADU, asking the the most questioned question “how much does it cost to build an ADU?” Below we have proudly brought to you the full cost breakdown and essential information for building an Accessory Dwelling Unit (ADU) in Los Angeles. Whether you’re looking to generate rental income, add extra living space, or increase property value, this guide provides insights into the factors influencing costs and various ADU types.

Here is all the necessary information you need to know before you proceed with your ADU project.

The costs of building an ADU have two main types of costs

  • Floor Plans & Permit Costs
    Cost range for designing, and obtaining permits $6,000 to $20,000+ to learn more about the plan design costs and permit fees click here.
  • Construction Costs
    The construction cost varies significantly when comparing the conversion of an existing garage to the construction of a new ADU. The pricing difference between the two is substantial. In the guide below you will find the answers for each project:

With the guide below will be able to calculate a rough estimate of the costs you will be facing during your project. To discover a more accurate estimate cost, you can use our ADU building cost calculator:

The cost of building an ADU may widely vary depending on a number of factors, including the type of structure, the size of the addition, the amenities you want to incorporate, the quality of materials you choose, finishes and fixtures, and the contractor you hire to build it. Therefore, it is hard to predict the exact price for the construction of your new unit.

Other than the plan costs and permit fees, the factors that image the ADU building costs are the choice of finish materials, the location of the ADU either it’s located on a hillside or flat. These are main key factors that can potentially fluctuate the cost of your ADU. Sincerely speaking, the final cost of building an ADU depends on numerous elements.

There are different types of ADU. These include:
How Much Does A Garage Conversion Cost in Los Angeles?

  • New construction detached ADU
  • Adding ADU on top of a garage (second story ADU)
  • Converting existing attached garage conversion to an ADU
  • Detached garage conversion ADU
  • Attached ADU
  • Junior ADU

Schedule free consultation with our specialist to get building cost estimate, click here to schedule free phone consultation.

It is important to keep in mind that these are only the construction costs: The phases of the building ADU include demolition, foundation, framing, roofing, plumbing, electrical work, etc. If we are working on a new structure, you will save demolition costs but will need to include foundation costs. On the other hand, if this is a garage conversion and there is an existing foundation, then you are able to save foundation costs in this scenario.

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

You can expect to spend somewhere between $70,000 to $320,000 for your new custom-build ADU.

How much does it cost to build an ADU in Los Angeles?

The minimum cost of building a legal 400-600 sq ft ADU with a one master bedroom, kitchen, guest bathroom, living room and storage closet and possibly space for a washer and dryer can typically start at a minimum of $100,000 to $120,000 (including floor plans, fees & permits).

How Much Does It Cost to Build a Detached ADU?

The cost of building a detached ADU starts at a minimum of $110,000 and may vary due to the design of the building and its distance from the main street, the building cost of a 1,200 sqft detached ADU that features two bedrooms and three bathrooms can be anywhere from 240,000$ to 480,000$.

Constructing a detached ADU, complete with its own address and utility bills, incurs higher costs compared to an attached ADU. This is due to the necessity of installing new connections and a distinct additional address, with a separate meter and panel box that can be used to manage different utility bills. A detached unit, being physically and functionally independent from the primary structure, demands separate utility connections and a plumbing system, making it the most expensive type of ADU.

How much does it cost to build 400sqft ADU?

A new ADU of 400sqft built from scratch can range in cost between $120,000 to $200,000 based on requirements, site access, site-perp and more.

How much does it cost to build 500sqft ADU?

A new ADU of 500sqft built from scratch can range in cost between $150,000 to $220,000 based on requirements, site access, site-perp, distance to utilities and more.

How much does it cost to build 1,200sqft ADU?

A new ADU of 1,200sqft built from scratch can range in cost between $300,000 to $450,000 based on requirements, site access, site-perp, distance to utilities and more

How Much Does a Garage Conversion Cost?

For a quality garage conversion that gives you an ADU with a kitchen and bath, you can expect to spend anywhere between $100,000 and $120,000.

In general, opting for a garage conversion represents a cost-effective approach to constructing an ADU, given that the walls, roof, and foundations are already in existence. The building cost for such an ADU is minimized when the garage possesses an electrical connection and an easily accessible sewer system. Garage conversions are more budget-friendly compared to new construction ADUs, primarily because the existing garage structures can be repurposed. However, it is crucial to consider that if the current garage structure is in poor condition, a complete demolition and reconstruction may be necessary, making the garage conversion less economically advantageous in such cases.

How much does two car garage conversion cost?

Most two car garage conversions start at about $100,000 and can go up to $160,000 or more based on the garage condition, distance to utilities, finish materials choices and more.

How much does a three car garage conversion cost?

Most three car garage conversions start at about $150,000 and can go up to $200,000 or more based on the garage condition, distance to utilities, finish materials choices and more.

How Much Does It Cost to Build an Attached ADU?

An attached ADU is connected to the primary home, and it typically shares the electrical and plumbing system with it. For a 500 sqft attached ADU that features two bedrooms and one bathroom, you are likely to spend anywhere between 60,000$ to 200,000$.

ADU Price Per Square FeetADU Price Per Square Feet

New California state laws have made accessory dwelling units more practical than ever before for the Los Angeles homeowners.

Once determined that it is possible to build a secondary dwelling on your property, the cost will certainly be your first and foremost consideration. This calculation is not easy for many homeowners, particularly when done on a per square foot basis because it depends on a number of factors, including the complexity of the site and design, quality of materials, and requirement of utilities.

How much does it cost to build an ADU per Square Foot in Los Angeles?

  • $240 – $400 per sqft for Garage Conversion
  • $240 – $350 per sqft for a Detached ADU
  • $240 – $330 per sqft for an Attached ADU
  • $240 – $350 per sqft for a Second Story ADU

Factors That Determine The Cost Of Building An ADU

Below, we cover the different factors when determining how much an ADU will cost to build:

  1. How Big Is The ADU

Of course, a 400 square feet ADU will cost less than a two-story 1,200 square feet ADU. Therefore, when calculating the estimated cost of putting up an ADU, the contractor is likely to cost per square foot and give you an average cost.

However, note that the total cost per square foot will go down if you are putting up a substantial ADU. Therefore, when constructing an ADU, it is advisable that you construct to the maximum size that is allowed to maximize the value of the property.

  1. Finish Materials & Design

Quality of the materials affect the total cost of putting up the ADU. A high-end design will cost more in terms of materials. The standard cabinets, doors, windows etc will put the project with less expenses and more simple installations which will reduce the resources to put up.

What are Material and Labor Costs?

The quantity and quality of the material will also have an impact on the cost of your ADU. The more quality materials you choose, the higher cost you will end up with;

These materials may include; 

    • Structural Materials
    • Doors and windows
    • Finish Materials
    • Fixtures and Appliances
    • Furnishing

The labor costs will widely vary depending on the contractor you will hire.

How Many Bedrooms and Bathrooms?

The kitchen and bathroom are the two costliest rooms to build on a per square foot basis. This is so because, unlike larger homes, ADUs do not feature large bedrooms or dining areas that are relatively less expensive to build as compared to full-fledged bathrooms or kitchens.

  1. City Regulatory Requirements & Fees

Approvals from the Los Angeles building and construction regulatory body can sometimes be costly. Consider the regulatory costs, such as “Plan check” which will vary depending on factors like the type of the floor plans you need to approve, and city the property is, city inspections, and more.

If your property has an open case with the local building code enforcement, it will make the process of obtaining an ADU permit more complicated which increases the total cost. Click here to search for open building violations.

  1. Engineering & Location

The process of putting up an ADU will require multiple specialists including architects to provide a proper floor plan that will be approved by the local authorities and include the extra costs of the construction because of the distance from the main street which is the location of the connections to the city utilities.

The cost of your ADU will be significantly low if it is possible to tie the existing utilities of your main house.

Are Separate Utilities Required?

Another factor that comes into play is how electrical, mechanical, plumbing, and HVAC utilities are going to be set up? Separate meters vs joint, sewer connection, solar panels requirements, etc’.

  1. Condition Of The Site

If the property is on wetlands or conflicting utilities, or requires demolition / foundation or both, it will affect the total cost of the ADU building. If you are planning on garage conversion and the garage is in good condition which allows it to use its foundation it will help the total cost to remain lower.

New Construction or Conversion?

Typically, the cost of converting an existing garage is around one-third less than building one from scratch. This is because the foundation, framed walls, and roof are already in place. However, it largely depends on their condition. If these elements are in good shape, you would not need to rebuild them, which will significantly bring down the total cost of your ADU.

However, if they are in poor condition, the ultimate cost of your converted garage will not be much different from what new construction would cost and sometimes even more.


Calculating the cost of an ADU on a per square foot basis can be misleading since there are many variables that will decide whether you will be on the low or high end of the estimate. Therefore, the cost of construction for the ADU of having the same square footage can vary significantly depending on the contractor.

In the city of Los Angeles, ADUs prices start at around $100,000 and go up to $300,000 based on their size, type, and quality of construction.

The best way to determine how much it would cost to build an ADU per square foot on your property is to consult with an experienced and reliable contractor.

We have created ADU building cost estimate tool and it’s free:

Find out if your eligible to build an ADU:

Talk to our specialist to find out the estimated costs of your ADU:

Let Us Design and Build Your Dream ADU

For years, we at CCS Inc (Construction & Consulting Services) have been helping homeowners in the greater Los Angeles area in bringing their visions to life.

Whether the goal is to expand an existing house vertically, horizontally or separately from the main unit, we can help you to get the most of your investment including estimated cost of your project upfront, and where it will put your property value when the construction is done.

We offer the full range of services starting with free onsite consultation, designing floor plans, to helping you in obtaining city permitting and assisting you in material selection to executing the actual construction, we will work side by side with you to translate your vision into a practical plan.

Schedule free consultation with our specialist to get building cost estimates:

Addition to your current house structureATTACHED ADU »
Add separated independent ADUDETACHED UNIT »
Convert the garage to an ADUGARAGE CONVERSION »
Convert any space of the main house, or add a new floorINTERIOR CONVERSION »
Add more than one ADUMULTI TENANT ADU »
Maximize the square footageJUNIOR ADU »

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