ADU Costs
We're ADU Cost Experts
When building an Accessory Dwelling Unit (ADU), having a clear understanding of all the costs is essential.
At Alto Builders, transparency is key, especially when it comes to the expenses involved in your ADU project. Since we handle everything from design and permitting to construction, we have firsthand insight into every potential hidden cost that may arise along the way.
The process of building an ADU involves multiple layers, from initial planning to the final construction stages. Our extensive experience in ADU design and build allows us to anticipate and manage unforeseen costs that often go unnoticed during the design and permitting phases. We take responsibility for identifying these potential challenges, drawing on our deep knowledge of real-world ADU costs.
On this page, we’ll explore the full range of costs associated with building an ADU, covering all the variables that can affect the final price in the Los Angeles area. Our goal is to provide you with a realistic financial outlook for your ADU project.
How much does it cost to build an ADU?
For budgeting purposes, expect the cost of building a turn-key detached ADU to range from $350 to $500+ per square foot, for units between 500 and 1,200 sq. ft. Around 80-85% of these costs cover the vertical construction of the ADU, which includes the building itself and standard finishes.
To calculate the all-in cost for your ADU, be sure to include additional expenses for design (about $12K), permitting fees (around $2-14 per sq. ft., depending on the city), and typical site work (approximately $25K). You should also plan for $30-50K+ for utility upgrades and other property-specific requirements. At Alto Builders, we assess over 75 specific ADU factors for each property to provide an accurate breakdown of all costs related to your ADU build project.
The cost of building a detached ADU is primarily influenced by the unit’s size, the number of units, site conditions (such as grading and utility locations), and local permitting requirements (like building plan checks, permitting fees, and school fees). Vertical construction costs will vary depending on the final finishes; our pricing includes a standard finish level, which covers appliances and fixtures. Learn more about our standard features.
It's important to note the recent rise in construction costs, which has caused sticker shock for many homeowners. The California Construction Cost Index (CCCI) increased by 37% between January 2021 and January 2024. This means that an ADU costing around $300,000 to build in early 2021 would now cost approximately $410,000 in 2024.
As of June 2024, our cost estimates for ADUs in Los Angeles have been updated to reflect these changes. Our goal is to provide a realistic understanding of the costs involved, so you aren’t met with unexpected expenses later. For more information on our pricing approach and our price guarantee, check out our detailed pricing page. Being informed from the beginning helps you plan more effectively for your ADU project.
What's included in the cost of building an ADU?
ADU Feasibility Study:
$7,500.00
There is no minimum lot size requirement for ADUs in California. Local municipalities are required to allow at least an 850 sq. ft. one-bedroom or a 1,000 sq. ft. two-bedroom ADU with only 4-foot side and rear setbacks, and many cities permit units up to 1,200 sq. ft. Additionally, an 800 sq. ft. ADU must be allowed “by right,” even if it encroaches on front setbacks or exceeds floor area ratio (FAR) limits.
Construction Drawings:
$7,500.00+
Many impact and development fees for ADUs have been waived, and certain remaining fees can be reduced by understanding key square footage thresholds that trigger higher fees (e.g., 500 sq. ft., 750 sq. ft., 1,000 sq. ft.). Additionally, some cities offer further fee waivers to support ADU development.
Permits & Fees:
$5,000.00+
Owner occupancy requirements for ADUs have been removed, allowing you to add ADUs on rental properties. Recent state regulations have permanently eliminated the need for owner occupancy, making it easier to develop ADUs.
Why does it cost so much to build an ADU?
We often are asked why Accessory Dwelling Unit building costs seem higher when compared to a Single Family Residence (SFR) on a cost per square foot basis. In short, the answer is that SFRs are often twice the size of an ADU, resulting in a lower price per square foot. ADUs have a higher cost per square foot because they bear many of the same “fixed” costs of any residential building project.
Whether building an ADU or a SFR, there are certain base costs which occur no matter the size of the structure.
These include:
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Design & Construction Documents: Relatively speaking, drafting hours and costs are in the same ballpark for an ADU or a basic SFR. An ADU still requires a full set of building plans… even pre-approved plans are not something you can walk into a building department as-is; they must be customized to your property.
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General Conditions: Dumpsters, temporary toilets, project supervision, and site protection are required regardless of the build size and will be part of your ADU costs.
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Kitchen, Bath & Laundry: Kitchens are the most expensive room of a building, including cabinets, countertops, plumbing & sink, plus appliances. Bathrooms and laundry facilities are also costly with plumbing & finish materials. A small one bedroom ADU still needs a kitchen and a bathroom, while a modest SFR might need just an additional bath yet support 4X the square footage.
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Vendors: Whether a vendor is installing a small amount of material for an ADU or a large amount for a SFR, there is a base cost for simply showing up and setting up their tools.
Thus, there is a minimum base cost to build a residential unit, no matter how small the unit may be. That means that an ADU cost per square foot can be as high as $500+ for very small units.
Read more about how to compare ADU quotes. Looking to go a more DIY route to save money? Consider an unfinished shell ADU, where you complete the finish work yourself and save.
HOAs
HOAs (Homeowners Associations) and CC&Rs (Covenants, Conditions & Restrictions) cannot impose unreasonable restrictions on ADU development. We design ADU exteriors to seamlessly blend with the main home, ensuring they meet the required standards for exterior finishes.
Parking
Most parking requirements have been eliminated, with no parking needed if the ADU is within 1/2 mile of public transit or car share services. If parking is required, it can often be easily addressed by designating spaces on the driveway.
Application Review
Building departments are required to respond to ADU applications within 60 days, and many act even sooner. However, this doesn’t guarantee quick approval, as the overall permitting process typically takes 3 to 8 months.