top of page

Understanding Accessory Dwelling Units (ADUs)

What is a Unit?

A unit is an apartment - an independent living facility for one or more persons, independent of the primary dwelling unit, which includes permanent provisions for living, sleeping, eating, cooking, and sanitation, with the exception that a Junior Accessory Dwelling Unit (JADU) may share a bathroom with the existing single-family dwelling to which it is attached.

What is an Accessory Dwelling Unit (ADU)?

Per SD information bulletin 100: "An Accessory Dwelling Unit is an attached or detached residential dwelling unit that is 1,200 square feet in size or less, provides complete independent living facilities for one or more persons including permanent provisions for living, sleeping, eating, cooking, and sanitation, and is located on a lot with a proposed or existing single dwelling unit or multiple dwelling units."

The original intent of ADUs was to provide housing for a family member or to generate supplemental rental income for homeowners; hence, these are sometimes referred to as "granny flats". Recent zoning changes, however, have eliminated owner-occupancy requirements and vastly expanded the scale of what can be built on single-family properties.

What is a Junior Accessory Development Unit (JADU)?

A Junior Accessory Dwelling Unit (JADU) is a dwelling unit that is 500 square feet or less in size and is contained entirely within an existing or proposed single dwelling unit, attached or detached garage, or attached or detached ADU, on a residential single dwelling unit lot. A JADU may include separate sanitation facilities or may share sanitation facilities with the single dwelling unit.

How tall can an ADU be?

The City of San Diego allows "granny towers" of up to 30 feet, enough for a three-story building.

The City's excessive height allowance was not required by State law, and Neighbors For A Better San Diego requests that the City amend its zoning to reduce the maximum height to 16 feet, which would still be in conformance with State law.

Do ADUs need to obey setback regulations?

NO!!! The latest zoning changes adopted by San Diego in October 2020 eliminated rear and side yard setbacks for ADUs, even though the State would have allowed 4 feet.

Does the owner of the property have to live on the premises?

For an ADU, the answer is no. This means that the developer who overbuilds the property doesn't have to live with the mess they create.

As single-family homes are redeveloped into high-income rental properties, they will most likely be flipped to real estate investors, who may reside outside of California or even outside the United States, moving our zoning decisions even further from local control by San Diego residents.

If an ADU can be taller and bigger than the pre-existing house, and the owner doesn't even live there, then why do they call them "Granny Flats"?

The term "granny flat" makes it sound like all these zoning changes are about homeowners caring for family members, instead of allowing developers to outbid homeowners for properties and turn them into mini-dorms, short-term rentals, and other high-rent developments.

Do ADUs have to be so ugly?

It is unclear whether this is considered a problem or a feature by City planners, but San Diego does not allow any architectural review of ADUs during the permitting process.

What is a Transit Priority Area?

In accordance with SB 743, “Transit priority areas” are defined as “an area within one-half mile of a major transit stop that is existing or planned, if the planned stop is scheduled to be completed within the planning horizon included in a Transportation Improvement Program adopted pursuant to Section 450.216 or 450.322 of Title 23 of the Code of Federal Regulations.”

Why are TPAs important?

Transit priority areas (TPAs) are important to ADU development because the number of ADUs permitted by San Diego on a single-family lot depends on whether the property is located inside or outside of a TPA. Approximately 60% of San Diegans live inside of a TPA.

Outside of a TPA, a developer can build one market rate ADU and one affordable ADU on a single-family zoned property.

Inside of a TPA, a developer can build an unlimited number of ADUs on a single-family zoned property as long as one less than of half of them are designated as affordable housing.

State law does not mandate San Diego's bonus ADU formulas and does not distinguish between a property being inside or outside of a TPA.

Wait. I need algebra to express how many ADUs are permitted on a property?

Yes. The number of ADUs permitted on a single-family lot inside a TPA is 2N+1, where N is the number of affordable units being built. That is, a developer is entitled to one base market rate unit and then one additional market rate unit for each affordable unit that they build.

Do the affordable and market rate ADUs have to be the same size and configuration?

Deed restricted ADUs shall be comparable to the market rate ADUs in either the number of bedrooms (plus or minus a bedroom) or the square footage (plus or minus 15%).

This is not specified in the code itself, but rather specified by the the SD Housing Commission.

What is SB 9?

Senate Bill (SB) 9 is a bill that has passed the State Senate and is now pending in the Assembly. This bill allow existing single family lots to be split into two parcels. Additional ADUs are then allowed on the two parcels to the limits allowed by state law or local ordinance, whichever is greater.

Neighbors For A Better San Diego opposes SB 9.

What is SB 10?

Senate Bill 10 (SB 10) would authorize a city or county to pass an ordinance, notwithstanding any local restrictions on zoning ordinances, to zone any parcel, including a single-family zoned parcel, for up to 10 units of residential density, at a height specified by the ordinance, if the parcel is located in a transit-rich area, a jobs-rich area, or an urban infill site.

Neighbors For A Better San Diego opposes SB 10.

bottom of page