What are the New Accessory Dwelling Unit Regulations?

By Sean Canning

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

So, what exactly is an 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 before you can qualify for an accessory dwelling unit. 

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.

San Diego ADU Setback Regulations

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 in the new accessory dwelling unit regulations in the city of San Diego. 

As I'm recording this video, there are lots of options for homeowners + rental property investors in this city looking to develop ADUs. 

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 property line, 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 (if it's facing 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. 

San Diego ADU Parking Regulations

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. 

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 because it will rent 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. 

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. 

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 impact fees in your neighborhood.

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 impact fees are 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.


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