A duplex is a residential property with two living units. They usually have one owner but can be occupied by two households. Owners have the option to live in one unit and rent out the other, rent out both, or occupy both units.
Simplex townhouses refer to properties in sectional title developments constructed on a single level. Duplex refers to properties stacked one above the other and is also the sectional title.
Renting out part or all of your duplex can result in tax deductions, access to multi-family financing, and rental income pays for your investment.
There are 27 Duplex in San Mateo County, CA currently.