Discover The Latest San Diego ADU Regulations

By Sean Canning

Accessory dwelling units (ADUs) are a term that comes up in our San Diego architecture firm quite a bit.

You may hear them referred to as companion units or granny flats or Casita's or guests, guest homes. But the correct term right now is accessory dwelling unit or ADU. This is not to be confused with a JADU (which I'll make a separate video about).

What we'll be discussing today relates to both detached ADUs as well as single-family or multi-family designs.

So, what exactly is an Accessory Dwelling Unit (ADU)?

Basically, it's a second home on a property that already has an existing home or dwelling unit. You have to have that first dwelling unit (the existing structure) before you can qualify for an accessory dwelling unit. They can come in several different configurations - such as a detached ADU and attached ADU.

Now in the city of San Diego, if you're in the RS zone, which is a residential single-family zone, you can qualify for one accessory dwelling unit and one junior accessory dwelling unit (ADU or JADU).

Photo of ADU project in San Diego by Ten Seventy Architecture

ADU Setback Regulations in San Diego

But if you're in the RM zone, you cannot do a junior accessory dwelling unit. But you can do a detached accessory dwelling unit in certain cases, if you're in the transit priority, overlaid. You have the option to leverage the affordable housing density bonuses, and to do more than two accessory dwelling units.

This is a very interesting time to be involved in the construction of an ADU project in San Diego County.

As I'm recording this video, there are lots of options for homeowners + rental property investors in this city looking to develop ADUs. I've been following the accessory dwelling unit regulations for over a decade now and in the past few years we've seen significant changes in what San Diego allows regarding its ADU requirements.

For example, to build in RM zones that are also in the TPO (transit priority overlay zone). So these are properties that we look at very highly now.

One key thing to note is that an accessory dwelling unit in San Diego has to have the same front yard setback as your primary dwelling unit.

And if you're on the corner lot, it also needs to have the same street side yard setback, but that doesn't apply to the rear or side yard setback. In those cases, you can actually use a zero lot line condition in the city of San Diego.

I know in other counties you can go four feet, but in the City of San Diego specifically, you can go right to zero, zero lot line condition, which is pretty wild.

Now, in most cases, you're going to want to leave at least four to six inches. Just in case you need to do something like run a subgrade drain over there or run a gutter, for example, a half-inch from that property line.

Just keep in mind, if you do go half inch from that, you may have to use scaffolding on your neighbor's property or in the alley behind your property.

So there may be some reasons why you can't build a zero lot line. A couple of words of caution - If you are going zero lot line, and you want a window, it has to be three feet from the property line.

However, if you go with a zero lot line condition and build a wall right on the property, you can use glass looking away from the property line. So in certain cases, this may work better for a courtyard condition that you're planning.

Parking Regulations For ADUs in San Diego

So that covers the setbacks. Now what about parking?

Fortunately, ADUs do not require any parking. So that is huge because that's going to allow small homeowners that want to develop their lots or larger developers to plan more ADUs in San Diego without the consideration of parking.

And as we know, parking is one of the biggest obstructions for new development in San Diego. This, along with getting a building permit, continues to be one of the more frustrating parts of the current ADU laws.

Now, just because you can do this, doesn't mean you always should do it.

In fact, whenever possible, I would recommend that you save a parking space off the street for your ADU can be rented for more.

It's very inexpensive to provide a parking space if you have the space on your lot. So it's really only the scenarios where the lot is so tight and you cannot fit parking when it would make sense to not include a parking space.

Now the other thing I should mention about parking is if you do build an ADU, you're now allowed to put your parking in your setbacks, particularly the front setback, which is otherwise restricted.

So there could be 15 or 20 feet in the front yard of your home which you cannot build on. But if you have a driveway and you build an ADU, you're now allowed to demonstrate that as having parking.

You can look in chapter 14 of the municipal code for the parking regulations that are very specific, uh, widths that you need to obtain to get a parking space, um, on your lot to have it verified as an ADU.

San Diego ADU Size Regulations

Okay, so we covered setbacks. We covered parking. What about the maximum size of these things?

Well, you can build a 1200 square foot ADU on any residential zone lot in San Diego provided you could fit it. So that would be RS or RMS zone lots. And if you're in the RM zone you could build two 1200 square.

So for context, a1200 square foot ADU could be a three bedroom home. So you can now see that the ADU could actually function just like a standard home. And in my particular case, we had a 550 square foot home and we're building a bigger accessory dwelling unit on that lot.

In the previous code, they used to limit the size of accessory dwelling units to 50% of the size of the primary dwelling unit.

But that's no longer the case.

Photo of the interior of an ADU development project

So you can now build an ADU larger than an existing dwelling unit. You could put it in front of the existing dwelling unit. It can be taller than the existing dwelling unit.

And that brings us to our next subject of height. In most residential zones in the city of San Diego, you're going to have a maximum height limit of 30 feet.

And in some cases, 40 feet in some of those RMS zones. That is going to be the same height limit for our ADU and our dwelling unit.

And there's really no way around that. However, there is something called an angle to plane restriction and you can look this up on my YouTube channel if you want more information, but essentially at the side yard set up.

You can build 24 feet high and then you have an angle which angles up to 30 feet. Well, it's been determined that that angled plane restriction is a type of setback.

So while that applies to your proper dwelling unit, that does not apply to your accessory dwelling unit. So this means ADUs can actually be taller at the side yard setback, because they can encroach into this angled plane restriction.

So this is pretty huge - it means your ADU can be taller in many cases than your primary home.

If you are looking for more information, check out our ADU Resource Center.

An Overview of the Fees That Come With Building an ADU in San Diego

So anytime you're going to build a project in San Diego, you can expect at least four fees from the building department.

The first is your impact fee, which is based on the neighborhood. So you can Google San Diego impact fee neighborhood schedule, and you can see the cost of the fees you will need to pay in your neighborhood according to the latest San Diego requirements for ADUs.

So if you build a one new home in San Diego, you're subject to one impact fee. If you build two new homes, you're subject to two impact fees (and these fees are a one-time payment). So this fee is the first thing that you're going to get hit with.

The next thing you're going to get hit with is your sewer and water fees. I believe the cost of these currently are around $7,200 for dwelling units.

The next fee is going to be your school fees for supporting public education in the city. However, this only kicks in at 501 square feet. So if you build an ADU under 500 square feet, you're going to be exempt.

But if you go over 500 square feet, you are subject to this fee. For this fee, assume you will be charged $4 and 8 cents per square foot. And that's a one-time payment you make to San Diego unified schools.

And the last fee that you're going to pay is for your plan check and inspection fees. Your plan, check and inspection fees are going to be almost exactly the same because it's mostly based on square footage.

ADU Rules and Regulations Regarding Permits

When it comes to building an Accessory Dwelling Unit (ADU), there are a number of rules and regulations that must be followed in order to obtain the necessary permits. These regulations can vary depending on where you live, so it's important to do your research before you begin your project.

To help you understand the top permitting fees that your ADU project may be subject to, we've embedded a helpful video below.

In this video, you'll learn about the various permits you may need to obtain, as well as the fees associated with each one. Watch this video to ensure that you're fully informed about the permit process and can avoid any unexpected costs or delays.

Accessory Dwelling Unit Regulations FAQ

San Diego housing will be dependent on ADU and JADU development continuing to be incentivized. Below are a list of answers to common questions we field regarding San Diego's ADU program.

By reading, you should have all the information you need to get your ADU constructed.

What Is The Definition Of An ADU?

A.D.U. stands for Accessory Dwelling Unit. These are legal structures that always serve as an accessory to a primary Dwelling Unit.

You may have heard the term being used more frequently in the last few years because the newer allowance of ADUs has been the primary strategy to alleviate California’s housing crisis. Typically the municipal fees for ADUs are significantly less than they would be for a primary Dwelling Unit of the same size.

Every municipality has different regulations for ADUs. In general, they can range in size from 150sf to 1,200sf. Some cities restricted the maximum height to16-feet while other cities allow them to be taller. Sometimes certain setbacks are reduced. Some zones/municipalities allow multiple ADUs on a single lot.

How Long Does An ADU Project In San Diego Usually Take?

The first few weeks of a new ADU project are spent requesting record drawings, measuring/documenting the existing conditions, researching relevant codes, + meeting with municipal staff to get clarification on development options.

More complicated projects may require a formal preliminary submittal to obtain the needed clarification to move forward with the design. As with most construction projects, the size of your ADU and overall scope of work determines how long it will take from start to finish.

Once we’re able to begin design we will go through a predetermined amount of meetings, progressing the design forward in each. The goal of this process is to move from more vague ideas to more detailed specifications.

Smaller ADU projects can take as little as 2 months to design while larger ADUs will take longer.

When the design is completed we are ready to produce our architectural construction drawings + begin any engineering needed. This phase can take one or two months depending on the complexity of the ADU + site conditions.

Now we’re ready for permitting!

Although the State of California requires ADU projects to be permitted within a 60 day period, real-world permitting timelines are highly variable, ranging from as little as 3 months for more straightforward projects to well over a year to achieve the more difficult permit types required for certain projects.

Construction is also highly variable + will depend mostly on your general contractor. Even smaller construction projects will take at least 6 months. Larger projects can take a year or more to complete.

How Much Does An ADU Project Cost In San Diego?

Custom ADUs can be more expensive than expected so it’s important to have an understanding of the costs before you begin your project. To answer this question let's break the project into a few categories below.

Soft Costs include design, engineering, consultants, + permitting. Every ADU is different + will require different professionals. Most projects we work on include an architect (obviously), a structural engineer, + an energy consultant (who produces the “Title-24 Report”). In California, the submittal package for an ADU permit can be pretty intensive so we have set a minimum fee of $20k for our architectural design package.

Permitting is also a type of soft cost. Permitting will vary greatly in price depending on the municipality + the type of permit. A Coastal Development Permit or Site Development Permit will be considerably more expensive than a more simple permit. Municipal fees for ADUs are usually reduced in comparison to a standard home of the same size.

Hard Costs are directly related to construction including materials and labor. Since the beginning of the global pandemic construction prices has increased. Currently in Southern California minimum construction costs are around $250-300 per square foot. A custom ADU will increase in the cost depending on the features + finishes. It’s also important to understand that a smaller ADU may cost more per square foot than a larger ADU.

If you are looking to achieve a high-end ADU design but have a tight budget to stick to, definitely consider our pre-approved ADU plans.

What Is A Junior Accessory Dwelling Unit?

A JADU or Junior Accessory Dwelling Unit is a specific type of accessory structure. JADUs come with specific restrictions + cannot be permitted on every lot. JADUs are generally limited to 500sf + need to be attached to another structure.

Can You Build Multiple ADUs On One Lot In San Diego?

Some zones/municipalities allow multiple ADUs on a single lot. Typically multi-family zones or transit priority zones are where multiple ADUs are permutable. Each municipality regulates ADUs slightly differently. Most single family zones allow an ADU + a JADU.

Crash Course On Designing an ADU in San Diego

If you're considering building an ADU in San Diego, there are a lot of things to consider (as you can certainly tell by now). You need to evaluate your property, figure out what you can build, and design a space that meets your needs. It can be overwhelming, but we've got you covered.

Check out the video below from San Diego architect Sean Canning for an in-depth overview of what it looks like to undertake an ADU project. In this video, Sean walks you through his process for evaluating properties and shares tips for the top things to look for before purchasing a property for future development.

View Transcript

Check Out More of Our ADU Blog Articles + Videos

As a leading San Diego Modern architecture studio specializing in ADUs, we regularly produce helpful content aimed at helping homeowners and property investors research their project. From design tips to financing options, we have plenty of resources to help guide you through your ADU journey.

The Truth About ADUs in San Diego (What the DSD Won't Tell You)

View Post

The Difference Between a Companion Unit + an Accessory Dwelling Unit

View Post

What Type of Structures Can Be Built on a Residential Lot in San Diego?

View Post

What are the Benefits of a Detached Accessory Dwelling Unit?

View Post

Small Lot Subdivisions in San Diego

View Post

How Millennials Will Buy Homes in San Diego

View Post

Check Out More of Our Architecture Articles + Videos

As a leading San Diego Modern architecture studio, we regularly produce helpful content aimed at helping homeowners and property investors research their project. Check out some of our most recent articles and videos below.

Where to Buy a Home in the City of San Diego

View Post

Modern Home Design: Key Components and Features

View Post

A Guide to Estimating the Cost to Build a House in San Diego

View Post

What Is Minimalist Architecture? [+7 Great Examples of Minimalism] 

View Post

How an Architect Evaluates Lots in San Diego for Development

View Post

How Much do Permits Cost in San Diego?

View Post

Let’s Design Something Amazing Together.

We love working with clients that appreciate great design + modern architecture. If that sounds like you, let’s talk.

Contact Us