How to Turn a Single-Fam. Home into and a Duplex by Adding an ADU

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I'm sure you are aware of the housing shortage in many Bay Area cities, as well in other area of CA. As one means to try and add to units to the housing market the State of CA now allows for "Accessory Dwelling Units" (ADU's) in many places.

An ADU is a secondary dwelling unit with complete independent living facilities for one or more persons

and generally takes three forms:

 Detached: The unit is separated from the primary structure

 Attached: The unit is attached to the primary structure

 Repurposed Existing Space: Space (e.g., master bedroom) within the primary residence is

converted into an independent living unit

 Junior Accessory Dwelling Units: Similar to re-purposed space with various streamlining measures

The rules around ADU's can vary from city to city but in general ADU's are allowed in many zoning districts that are zoned single-family; they are often exempt from many Planning Dept requirements for parking, open space, etc; they often have a streamlined permitting process and typically cost less than building new rent-able square footage.

I am interested in getting involved in this type of investing/improvements and would very much like to connect with others who are as well. I think there is tremendous, untapped opportunity with ADU's in areas where real-estate prices can be extremely high.

Please get in touch if you would like to connect and discuss in more detail.


Jim Gallagher, Architect

lets connect i think i have an idea that would work out would like  your input..

In the City of San Jose(CA) there is now allowance for a new secondary unit up to 600 sf in gla and 60 sf in storage, a kitchenette etc. The home owners can now add legally have an in-law quarter or use it to rent out. It does not mean richness to the home owners. The additional sf when factored in sf with primary residence to bump the value is not perceived as an acceptable concept today. All the units are sold as if the additional sf improved never existed. There are no comps today to claim it is worth more by the appraisers. Once it is a R1 it remains as R1 with an added on unit that carries minute to no additional values.

The lots here are so small in this area the set back distance will prevent one to have a meaningful way to build another unit as SFH. The exception is larger lots > 9000 sf. Most people prefer to convert a garage into a living unit with often without a permit. A better way is add another room or two to make it a larger home. Most of the additions with separate entrances and unit is already in place under same home owner.

One plan that works is conversion of R2 to attached homes as 2-R1. There is no physical change to the home it needs to have a HOA with proper documentation. That I have seen a few in Campbell, Sunnyvale before the Great Recession. Still not too popular with steep duplex, triplex appreciations. If the owners can sell a duplex, triplex anywhere in SF South Bay in one week at over asked price; is there any need to convert to 2-R1, an upstairs third R1 today? I have a hard time envision that someone will ultimately want to own a section of a attached home that was a garage previously. In Burbank district of Central SJ they already exist some homes have split the lot from 6000 sf to 3-2000 sf and apply for zero lot grand father clause new parcels. These were built often without a permit from 1930s on and have grandfather clause for ownership.

you may pm me . I have a great contact in San Diego that really knows the adu space. Very exciting for us too. Starting to see clients take advantage of this. The trick is get the city/county to allow this. Much needed.

Hey peeps,

Make sure you read really deeply into your town ordinances. I know in my town in RI they are allowed but there are certain qualitative perimeters that a building inspector would likely harp on. For instance, ADU’s here are only allowed for the very specific purpose of having your children build a secondary dwelling on your property. You CAN however use the intricacies of the code to your advantage by looking into what makes and ADU an ADU. then push the limits of an ‘occupancy space’ that doesn’t have an oven let’s say so it’s not a ‘kitchen’ and therefor not an ADU but you could still build. Does that make sense?

I’m also no legal expert. My guess is lawyers will tell me it’s illegal and everyone else will tell me they’ve done it once or twice, idk 🤷🏻‍♂️

That’s from my very very brief experience,



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