What is an Accessory Dwelling Unit? An accessory dwelling unit (ADU), commonly known as a secondary or in-law unit, is a residential unit developed within an existing residential building. ADUs are typically developed in an underutilized area of the property. This could include a garage, lower level storage areas, attic space, etc.

Will my building qualify? The development of an ADU is typically subject to the satisfaction of zoning, building and fire code regulations. ADU’s are currently allowed in districts zoned Residential so long as the density limits allow the addition of additional units.

Are there limits on the number of ADU’s Allowed? The City of San Francisco has programs that allow exceptions to the density limits. Buildings citywide that are undergoing Mandatory Seismic Retrofitting, can take advantage of these exceptions. This includes no limit on the number of units added with the exception of those in RH-1 and RH-1 (D) zoning districts.

How should you plan for ADU?
• The first step involves doing preliminary research. The City website below is a good start. This is where you can find if your building qualifies, if it has been identified as a candidate for a Mandatory Seismic Retrofit and if you’re in the right zoning district. If you feel you meet the basic criteria a visit to the planning department for a review and evaluation by a planner is in order.

• Once you determine that your building is a good candidate the next step would be a discussion with an architect who is well versed with the code requirements for ADU.

Important! In our experience the most successful projects take place when the architect who is working on the ADU is concurrently coordinating with the structural engineer who is designing the seismic retrofit. We have encountered several projects where the ADU was considered AFTER the structural design was completed and permitted. In these circumstances, the ADU design was restricted by the engineering work that had already been done and it caused unsatisfactory results.

Want to learn more? You can find more in depth information at the Planning Department’s website:

If we can be of help call us to schedule an assessment of your building
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