ADU: Added Space, Extended Family and Rental Income

ADUs are one of the most popular home improvements in the San Francisco Bay Area, and for good reason! ADU construction increases property value, adds space for extended family and can provide current and future rental income.

Accessory Dwelling Units follow most of the same guidelines as any addition, remodel or new construction, based on state guidelines in addition to local requirements.

4 Primary Types of ADU Construction For Space and Rental Income:

Generally speaking, there are (4) basic types of ADU options

Free standing ADU

Addition to existing home or garage

Addition and/or modification to an existing accessory building such as a detached garage or storage building

Remodel of existing interior living space and re-purpose of attached garage and storage space (within the existing footprint).

Free Standing ADU

This type of ADU construction is essentially a new house. It is built similarly to your primary residence, but on a smaller scale and to conform to local ADU requirements. These typically incur building costs similar to a primary residence (although finishes may be budget level if used as a rental).

Home Addition

Similar to a standard home addition, this is a living unit which is attached to the primary residence. This can be an upper floor, side addition or rear addition. Separate egress is required, and utilities may also be segregated. One convenient version is an addition above an attached garage.

Modification of Existing Accessory Building

Another type of ADU is a conversion and/or addition to an existing detached building on the property such as detached garages and larger storage buildings. These can be more cost effective than a new construction if the shell is in good condition. In most cases, these require utility upgrades such as sewer line as well as water supply and power needed for bathrooms and kitchens.

Remodel of Existing Space for ADU Construction

This version of an ADU is a remodel of existing space within the footprint of your home. Typically, this involves converting the garage and other ground floor storage space into a living unit. This is usually the most cost effective conversion, but you will lose interior parking and any converted storage. In some cases, a portion of the existing living space is allocated to the new ADU footprint.

The type of ADU that you choose will depend on your budget, lifestyle needs and intended purpose. An interior re-build appeals to many people if it is used for extended family. For future rental, a free standing unit or detached garage conversion will allow more privacy for the primary residence.

Given the high cost and scarcity of living and rents in San Francisco and the peninsula, ADU construction for space and rental income can be one of the best investments you will ever make!

In review, the options discussed above will vary in construction cost, based not only on the type chosen but also local ordinances, availability of utilities, site access and existing topographical details.

Your first step to exploring ADU construction options is with an initial conversation with BMF Construction at 415.699.9124 or email us at We look forward to helping you!

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