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What To Know Before Your First ADU Construction

Your first ADU construction likely comes with a lot of questions and unknowns. Get answers to all your ADU-related questions with Cottage.

January 1, 2018

It’s hard to know exactly what you’re getting yourself into when you start building your first ADU. From price to timeline to construction, the entire process can be quite overwhelming to tackle on your own. The good news is that it doesn’t have to be when you work with experienced builders like Cottage.

Whether you’re building your ADU on your own or with Cottage, here’s what you need to know before your first ADU construction:

What Is an ADU?

An accessory dwelling unit or ADU is a secondary housing unit that’s located on a single-family residential lot. ADUs have become increasingly popular in metropolitan areas such as Los Angeles and San Francisco in recent years, as they can help residents combat rising housing costs.

ADUs can be used for everything from entertaining and hosting guests, housing family members, and rental income. The possibilities are nearly endless with an ADU that functions as a second home in your backyard.

What Are the Different Types of ADUs To Choose From?

Now that you know the basics of ADUs, let’s cover the three different types you can choose from:

1. Conversion ADU

A conversion ADU involves converting a part of your home into an ADU by adding a bedroom area, separate bathroom, and kitchen area. For instance, you could convert your basement into an ADU. You could also convert your garage or a large guest bedroom into an ADU with the right design and plans.

2. Attached ADU

An attached ADU involves building an addition onto your existing home that then serves as a separate unit complete with a bedroom, bathroom, and kitchen. Many people choose to add another bedroom or bathroom onto their homes, but in reality, you could add on a whole separate unit with a wall of separation from the existing home.

3. Detached ADU

A detached ADU involves building an entirely separate structure on your property. Detached ADUs often take the appearance of a tiny home or cottage, although they can be built to match any style or design specifications.

Building a detached ADU is often the best way to maximize your space, as they are completely separate from the main home, offering privacy and future rental income opportunity without becoming disruptive to your life.

Where Can You Build an ADU?

The state of California has made it easy for homeowners to construct ADUs on their properties, in part to address rising housing costs. However, specific restrictions and regulations are put in place by cities and counties.

Here’s what you need to know about building an ADU in three of California’s biggest cities: Los Angeles, San Francisco, and San Jose.

Los Angeles

In the city of Los Angeles, all lots zoned for single-family use can add one ADU and one Junior ADU (JADU). An ADU can be up to 1,200 square feet, and a JADU can be up to 500 square feet.

All units must have minimum setbacks of at least four feet from the side and rear lot lines, in addition to ten feet from any existing structures. Some units may be required to have one parking spot if you are not within a half mile of public transit.

Long-term rentals of ADUs are permitted in Los Angeles so long as they are more than 30 days. Additionally, owner occupancy is not required for permitting an ADU until January 1, 2025.

San Francisco

In the city of San Francisco, all lots zoned for single-family use can add one ADU and one JADU. A two-bedroom ADU can be up to 1,000 square feet, a one-bedroom ADU can be up to 850 square feet, and a JADU can be up to 500 square feet.

Detached ADUs can be no taller than 16 feet and are required to have minimum setbacks of at least four feet from the side and rear lot lines. There are no parking requirements for ADUs in San Francisco. Like Los Angeles, long-term rentals are permitted, and owner-occupancy is not required in San Francisco until January 2025.

San Jose

In the city of San Jose, all lots zoned for single-family use can add one ADU and one JADU. Single-family lots less than 9,000 square feet in size can add a detached ADU of up to 1,000 square feet, whereas lots more than 9,000 square feet can add a detached ADU of up to 1,200 square feet.

One-story detached ADUs can be up to 18 feet tall, and two-story detached ADUs can be up to 24 feet tall. ADUs must be set back at least 45 feet from the front property line and four feet from rear and side property lines.

Like San Francisco, there are no parking requirements for ADUs in San Jose. And like both Los Angeles and San Francisco, long-term rentals are permitted. Owner-occupancy is not required in San Jose until January 2025.

How Much Does It Cost To Build an ADU?

The cost of adding an ADU to your property depends on a whole host of factors, including where it’s located, how big it is, and what features you want it to include. Generally speaking, you can expect to pay about $350 to $500 per square foot to build an ADU from scratch. Of course, this depends on your choice of ADU design, finishes, and general site-specific conditions.

This is an all-in cost estimate that covers everything from design, engineering, permitting, site preparation, utility connections, foundation, and actual construction. To save money on your ADU costs, work with a comprehensive ADU builder that handles the entire process from start to finish. This approach can save you money over the traditional design-bid-build method, which requires you to do each piece of the process separately.

Does an ADU Add Value to Your Property?

If you’re considering building an ADU on your property, you’re likely concerned about earning your money back. Even if you’re planning on staying in your home for the rest of your life, you will likely want to know how an ADU can affect the resale value for those that inherit your home.

For starters, adding an ADU to your property increases its value by effectively adding additional bedrooms and bathrooms. So instead of a three bedroom, two bathroom house, you could sell your house as a four bedroom, three bathroom house with a one bedroom, one bathroom ADU.

However, ADUs don’t just add value in the traditional sense in terms of additional bedrooms and bathrooms. In fact, they add even more value since they are in high demand. ADUs are highly desired by homebuyers in California as they can be used as in-law suites or even potential rental units. Check out Cottage’s detailed analysis of the value an ADU can bring to your property.

How Long Does It Take To Build an ADU?

Even though adding an ADU to your property provides instant value, the building process itself isn’t instantaneous. Although timelines vary depending on location and other factors, including size, design, and builders, you can expect the construction of your ADU to take anywhere from four to 12 months depending on the size and complexity of your project.

If you work with an experienced ADU designer and builder like Cottage, you can enjoy a shorter overall timeline that should take no more than a year. However, the process could also take less time.

To get a better idea of your potential timeline, here’s a breakdown of the different components of the ADU process and how long each component takes:

  • The design and development stage can last anywhere from four to six weeks.
  • The permitting process can take anywhere from three to four months.
  • The actual construction process can take anywhere from three to five months.

Generally, Cottage ADUs are designed, permitted, and built within a 10-12 month timeframe.

How To Design Your ADU?

If you’re building a detached ADU, you’re essentially building a house from scratch. This means that you need to focus a lot on the design of the unit so that it’s functional, aesthetically appealing, and affordable.

The best way to design your ADU is to work with experienced ADU designers like Cottage. The experts at Cottage can help you maximize your space to come up with an ADU design that works for your unique needs.

For example, do you need a laundry room in the unit? They can make that happen. Are you looking for a lot of storage space with walk-in closets? They can design that too.

How To Build Your ADU?

Once you have your ADU design, it’s time to bring it to life during the construction process. However, managing a full-scale construction project on your own can be quite challenging. Custom ADU builders like Cottage take all the stress off your shoulders thanks to their team of vetted professionals.

When you work with Cottage, you will be paired with a licensed contractor that’s been vetted by industry experts and is fully licensed, bonded, and insured. To meet Cottage’s requirements, they must hold an active contractor’s license in good standing, bond and liability insurance of $1 million, and worker’s compensation insurance of $1 million.

The Final Rundown on ADU Construction

Since the ADU construction process can be quite detailed and intricate, the most peace-of-mind approach is to work with an experienced partner like Cottage, who can handle the details for you. Cottage handles everything from ADU feasibility to design, permitting, and construction.

Cottage’s designers can help you get the features you need in an ADU and our architects can make it happen with a functional floor plan. Finally, our builders can bring your vision to life with the highest quality materials and workmanship.

So reach out to Cottage today to get started on your ADU construction!


Accessory Dwelling Units (ADUs) | California Department of Housing and Community Development

California's New Accessory Dwelling Units Laws: What You Should Know | Forbes

Home prices are now rising much faster than incomes, studies show | CNBC