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Accessory Dwelling Unit

San Francisco ADU

Many parts of San Francisco including the Outer Richmond consist of single family homes zoned RH2 (Single Family, Two Units).  This may allow homeowners to build an Accessory Dwelling Unit, otherwise known as a legal in-law or second unit.  This being San Francisco always remember how difficult building anything can be as you continue reading this post, and confirm everything with the building department, Planning Department, architect, contractor, plumber, electrician, etc.  I want to make sure you don’t spend a few thousand dollars with an architect before finding out your home does not qualify for some unexpected reason.

San Francisco Map of Zoning

San Francisco Property Zoning Map

Accessory Dwelling Unit

Accessory Dwelling Unit (ADU) is a term the city is using to signify an additional unit added to a building, either a single family home or multi-unit, inside the envelope of the existing building.  For instance on the bottom floor behind the garage.  Essentially the city understands many properties have space that is not being used to its highest potential, and may provide an opportunity to the city to decrease housing demand.  In terms of this post I am also including actual second units.  A difference to think about is an accessory unit may not be able to be sold on its own, may not be able to get its own numerical address (788A 40th Ave as opposed to 790 40th Ave), is really an accessory to the larger living space above.

Why Add an Accessory Dwelling Unit to Your San Francisco Home?

Mortgage relief is a reason that quickly comes to mind.  San Francisco homes are expensive and wouldn’t it be great if a tenant could help you pay your monthly mortgage without intruding on your living space?  Another reason might be to maximize the rents for your home.  Renting out a house in the Outer Richmond might cost $4500/month, while set up as two units the same property might rent for $6000/month; $3500 for the upper unit and $2500 for the lower unit.  Take a look on  and see what homes are renting for in the Outer Richmond.  These are of course very rough numbers and will be completely effected by the quality and location of the existing unit and the added unit.

What Has Changed?

The population.  San Francisco is experiencing massive population growth.  The United States Census Bureau estimates there are over 850,000 people in San Francisco as of 2014 up 5% from 2010 when the population was about 805,000:  45,000 people!  The population indicates demand.  On the supply side the 2014 San Francisco Housing Inventory Booklet states about 3500 units were built in 2014, and that is on the back of years of practically no construction due to the great recession starting in 2007.

The outcome of all this is the city is very interested in adding housing stock.  Adding units to existing buildings is one of the methods being used, which is why adding and legalizing units has become part of the discussion.  For homes zoned RH2, where the unit can fit in the existing envelope of the existing structure, adding units may be a viable option.

Housing Density

Outer Richmond ADU

As a home owner in the Outer Richmond I understand the anxiety involved in increasing housing density, a process happening in every corner of San Francisco.  If you live in the Outer Richmond, you know how wonderful the neighborhood is.  But you probably also know the cost of housing in the Outer Richmond is skyrocketing, and for many newer home owners adding a unit, or Accessory Dwelling Unit, could make the difference between having the time to enjoy the beauty of the area and just living to work.  For older homeowners it can make retirement much more affordable.

Legalize Your Illegal Unit

You may already have a unit tucked away behind the garage that you know is not legal.  Legalizing these units is also an option and can reduce the risk and stress of renting out your in-law. If this describes your situation take a look at the San Francisco Building Department site:  Legalize Your Illegal San Francisco Units

Things To Think About

1.  Just because you can add a unit does not mean it is always a good idea, or perhaps it is a good plan today but in the near future it will turn out to have been a mistake.  For instance, houses in the Outer Richmond are increasing in price at a quick rate.  Many people moving to the Outer Richmond do so because they like it as a neighborhood primarily of single family homes.  If you add a unit to your house it will no longer be a house it will be a two unit building, and once the deed is done there is very little chance to go back to a single unit.  This means, even if a single family is worth much more than two units in the future, you may be stuck with a property that is two units unable to convert the property back to a single family home.

2.  A home with an illegal unit that the city is aware of may be viewed by the city as a multi unit building as it relates to rent control, tenant evictions, etc.  This can also make it difficult to get permits to make the illegal space part of the main house if, for instance, you want to turn a two bedroom home into a four bedroom home by incorporating the downstairs square footage into the main part of the house.  Remember, building outside the existing envelope of a home is very difficult, so that downstairs square footage could become very valuable when added to the main house’s square footage.

3.  It could cost $300/square foot to add a unit.  That is $300,000 for a 1000 square foot addition.  Every property is different, so this is just a rough estimate.

4.  If you stay within the envelope of the existing property you may not have to go through a neighborhood review.  If you want to expand the envelope of the property, meaning you would like to push the back of the house out further into the back yard or add a floor above, the permit process suddenly becomes much more difficult and can take much much longer to complete, if it is possible at all.

5.  Changing the use of the property may be seen as a change to the underlying collateral by your lender and that may cause them to call your loan.  With rates as low as they are that may not be a big deal, but if interest rates shot up and you were forced to refinance your loan, it could a big negative and reduce the amount you actually make from renting the space.  Speaking with your lender is an important first step.

6.  If you are on the fence about making any upgrades, or you just don’t have the money to do it, you can still profit from this information because these are all concepts that can be sold to buyers as, what realtors call, upside potential.  Essentially, an Accessory Dwelling Unit, whether completed or not can add value to your property just by the fact that it may be possible to add.  It is also a great first step in understanding how to maximize the value of your home.

ADU Related Documents

I have the full sized San Francisco Zoning Map showing the different zoning in SF, I can send you the Accessory Dwelling Unit Handbook, and many other documents you may be interested in reading.  Email me or give me a call and I’ll be happy to send you what I have.  I am also happy to stop by your property and give you some ideas about what you could do with your home in terms of upgrading the existing use, or how to add a unit.  I can give you a good sense of where the market is heading and what will bring added value to your property.

Outer Richmond Accessory Dwelling Unit Zoning Map

What is the value of your property?

What is the likelihood of adding a unit to your property?

What is the state of the San Francisco real estate market?

Click the link below, send me an email.  I usually respond within an hour…unless it is the middle of the night.

Let’s Talk!


  • Sloan Smith

    I have a question for you. Feel free to answer if willing….

    I have a client trying to refinance multiple loans (1st, HELOC, and private money loan for construction) into one loan on a property in San Francisco. It is classified with the county as a two unit building. It has two separate addresses, has what you would consider an ADU, and is owner-occupied. An appraisal was done after completion of the construction, and it was deemed a single family with an accessory unit. This is leaving a potential inconsistency with the lender. Is this still considered a two-unit? From your post, it seems that it is difficult to go back to a single-family when a property is considered a two-unit (if you added a ADU). But what about if it’s already a two-unit, as in this case? Is RH2 zoning technically a 2 unit? Can an appraisal cause the designation (1 unit or 2) to change? Thanks.

    • Hi Sloan, thanks for asking the question. Anything to do with the city and its byzantine building codes is always complicated, and you have asked a multi-tiered question to boot.

      First off, an appraisal will not change the building designation as it pertains to the city. The appraisal is a private document paid by the buyer for the lender.

      RH2 is the zoning which doesn’t mean a building is automatically a two-unit building. I own a house that is zoned RH2 but it is definitely a single-family home. RH2 suggests it is likely the city would allow another unit to be built on the property if the owner went through the process of getting plans approved and going through neighborhood review, which is the process through which neighbors have the right to have a say about whether building plans are approved.

      If the house has an ADU (Accessory Dwelling Unit) it can still be designated as a single-family house with an ADU as opposed to a two-unit building. The process of adding an ADU is different from the process of adding a second unit to a property. Because this process is different you end up with a different kind of property, in this case, a single-family house with an ADU as opposed to a two-unit building.

      I didn’t completely understand you question, does the property have two units and an ADU or is it a single-family house with a small unit added in the garage, which is what an ADU usually is?

      Thanks again for your question!



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