How To Build a Taller ADU Than Your Primary Dwelling Unit in San Diego

By Sean Canning

Hi, I'm Sean Canning, Principal Architect at Ten Seventy Architecture, one of the leading experts in San Diego's accessory dwelling unit regulations.

Today I wanted to make a video to explain why in certain scenarios, you're allowed to build a taller Accessory Dwelling Unit, then you would be a primary dwelling unit.

Now to explain this, you have to understand this section of San Diego's municipal code that discusses the angled building envelope plane. 

Sometimes this is referred to as an "angled plane restriction" sometimes it's referred to as an "angled plane setback". And that's the key to this. You see, in most residential zones from the property line, you're going to take a required side yard setback. Which could be anywhere from three feet to five feet depending on a few different various things.

Now from that point, you have to go upwards 24 feet (27 feet in the RT zone - but for the purpose of this video, we'll use 24 feet) once you hit that point 24 feet above your setback, now the angled restriction starts to come in. And this angle is either going to be 30 degrees or 45 degrees depending on some criteria.

But the point here is on a narrow lot with two side yard setbacks and this angle of plane restriction, oftentimes you can never reach the maximum height that the base zone allows.

So on a 25 foot wide lot, your maximum height is going to be 29 feet. But here's where it gets interesting. Since Accessory Dwelling Units are not required to respect certain setbacks, they actually can encroach into this angle plane restriction, which means you can build a taller ADU than a primary dwelling unit on narrower lots.

An important thing I want to mention here is that certain front yard setbacks also come with this angle playing restriction.

But since the Accessory Dwelling Units are not allowed to encroach into the front yard, we also can't encroach into the front yard angled plane. So just be careful about that.

If you have any questions about angle planes or ADUs, please feel free to reach out. A good place to email me is

You can also check out our ADU Resources Center which will quickly get you up to speed on everything you need to know about building an ADU in San Diego.

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