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How to Build an ADU in California (The Ultimate Guide)

ADUs (accessory dwelling units) are small homes built within the side or backyard of a larger home, usually on property that’s already owned by the homeowner. If you’re interested in how to build an ADU in California, this ultimate guide will explain everything you need to know from permits and licensing to building materials and costs. Here are seven things to keep in mind as you plan your ADU project

An Accessory Dwelling Unit Explained

An accessory dwelling unit, or ADU, is a second unit on your property that can serve as a guest house, home office, studio apartment for aging parents or adult children returning home. It may contain its own kitchen and bathroom, but it’s not intended for full-time living. Instead, owners often rent out their accessory units via Airbnb and similar sites. The owner then uses that rental income to help pay off their mortgage while they live in their primary residence at no additional cost to them.


Zoning Laws For Building An ADU In California

California’s zoning laws dictate that an Accessory Dwelling Unit (ADU), or granny flat, must be built either within 300 feet of a single-family home or on a lot already zoned for commercial use. In other words, if you live on a single-family residential street, you can add an ADU as long as it is within 300 feet of your primary residence. If you don’t live on a single-family residential street, however, you may still build an ADU—but only on lots zoned for commercial use. There are many restrictions and requirements associated with building an ADU; these will vary depending upon whether your property is located in a planned development zone or not. If it isn’t located in one of these zones, it will fall under standard California zoning laws.


What Does The Process Look Like?

It’s important to know what you’re getting into and how it works before you make any moves. Luckily, there are four main steps involved with building a detached accessory dwelling unit. For example, step one is called On-Site Plan Review, which involves evaluating your site conditions and making sure your lot has enough space for a second home. If so, then you can move on to Step Two: Preliminary Design Review. This step requires that you submit plans for approval by your local planning department. Once they approve these plans, then you can move on to Step Three: Building Permit Application Submittal and Step Four: Construction Inspection & Permit Issuance. If all goes well at each stage of construction, then congratulations! You now have a new place to call home—or rent out as extra income!


Finding a Builder

The first thing you need to do is find a good builder. The best way to do that is to ask around, look on your city’s website for approved builders, or search online for ADU builder plus your city or county. Once you have several candidates, make sure they are licensed and have experience in permitting and builiding an ADU.

Time Line To Finish The Project
6-8 months is a good amount of time, but it will depend on your personal schedule and availability. We have gone as short as 4 months and as long as 12. The more time you take, however, usually means higher costs since contractor rates will be more expensive during busy seasons. Just make sure you are realistic with yourself about how much time you can dedicate to building your project. If you find that every day after work there are other things pulling at your attention and energy, then maybe building an ADU isn’t for you right now. But if it’s something that is truly important to do with your life, then don’t let anything stop you from making progress toward that goal!

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