Thanks to laws that went into effect January 1, 2020, building an accessory dwelling unit (ADU) – also known as a “granny unit” or “in-law unit” – is a more attractive option than ever for California homeowners who want to gain a little additional living space or get some rental income.
If you’re considering building an ADU on your property, here are some answers to the questions you’re likely to have.
Can I Build an ADU on My Property?
The first question most people have is, can I do this legally? Fortunately, in most cases, the answer is yes!
Before the state law changes, some local jurisdictions and homeowners’ associations (HOAs) enacted regulations intended to severely limit a homeowner’s ability to add ADUs to their property. Now, HOAs and local officials cannot enact ordinances that are more restrictive than the state’s regulations.
The main factors governing ADU construction are zoning and setback requirements. To build an ADU in California, your property must:
- Be in a zoning district that allows single-family or multifamily use;
- Accommodate a minimum side- and rear-yard setback for detached ADUs (unless you’re converting an existing structure; more on that below.)
Local jurisdictions can no longer impose minimum lot sizes for ADUs, as long as the setback requirements are met, but other local requirements may still apply, provided they don’t conflict with state laws. For example, in San Rafael, you can build an ADU of up to 800 square feet regardless of your lot size, and for an ADU of up to 800 square feet, there is no requirement to replace covered parking.
When planning your ADU, you should always check with your local building department if you have questions about what’s allowed.
What Kinds of ADUs Can I Build?
Conventional ADU
A conventional ADU is a self-contained structure, or a structure that is added on to the exterior of the primary residence.
Junior ADU
A junior ADU (JADU) is like a studio apartment within an existing or planned primary residence. It can share central systems and a bathroom with the main residence.
Garage/Carport Conversion
Garage or carport conversions are among the most popular options. These can be conventional or junior ADUs, provided they have at least an “efficiency” kitchen (for a JADU) or a full kitchen (for a conventional ADU), a bathroom and exterior access.
The good news is that if you’re converting a garage or carport to an ADU, the new laws stipulate that you can replace the existing structure with a new one that has the same footprint and setbacks as the prior structure, even if it doesn’t meet the required setback for ADUs.
How Many ADUs Can I Build on My Property?
You can now build one conventional ADU and one JADU on a lot zoned for single-family use where there is an existing or proposed single-family home.
In California, you can build two detached ADUs on a lot zoned for multifamily use and multiple ADUs up to 25 percent of the existing unit count within an existing multifamily building, provided you meet setback requirements and a 16-foot maximum height.
Where Can I Build an ADU on My Property?
Local building ordinances govern where on a lot you can build an ADU. Generally, all types of ADU can be built in a back or side yard, provided you can meet setback and any other local requirements. Some municipalities also permit an attached ADU or JADU in the front yard. Check with your local building department for ADU location requirements in your area.
What Are the Size Requirements for ADUs?
Under state law, local ordinances can’t restrict ADUs to less than 850 square feet, or 1,000 square feet for ADUs that contain more than one bedroom. Maximum height requirements must allow ADUs of up to at least 16 feet high.
JADUs can be a maximum of 500 square feet (an additional 150 square feet may be added to the existing dwelling to accommodate the required separate ingress/egress for the JADU.)
What Are the Parking Requirements for ADUs?
For conventional ADUs, you must provide one parking space per unit or bedroom if the lot is more than a half mile from public transit. Lots within a half mile of public transit are exempt from the parking requirement.
JADUs or garage/carport conversions do not require you to provide additional or replacement covered parking spaces.
Can I Rent Out My ADU?
Yes.
In addition, the new laws prohibit local agencies or HOAs from requiring homeowners to occupy either the ADU or primary residence until January 1, 2025. However, for a JADU, local regulations can require owner-occupancy of either the JADU or the main dwelling.
As always, your best bet when considering building an ADU on your property is to consult a local architect or contractor with experience in ADU development.
A version of this post first ran in 2020.