A secondary dwelling unit is an old but brilliant idea: having a second small dwelling right on the same grounds your regular family house, such as:
- an apartment over the garage
- a tiny house in the backyard
- a basement apartment
In spite of its physical form, legally an SDU cannot be obtained or sold separately, as it is a part of the main home. The SDU owner is the main homeowner.
Although secondary dwellings are an old idea, they fell out of favor in the middle of the 20th century. However now they’re coming back, and they have lots of names. Planners call them SDUs or ADUs (Secondary/Accessory Dwelling Units), but they’re also known as granny flats, in-law units, laneway houses, secondary dwelling units, etc. SDUs can be tiny houses, but tiny houses aren’t always SDUs.
People build them for various reasons, but the most common objective, according to one study, are gaining income via rent and housing a family member. Besides building an SDU takes less time, than a conventional house.
Many American houses are too big for 1- or 2-person households, which is too bad, because size is probably the biggest single factor in the environmental impact of a house.
If one has a reasonably sized house, and an even more reasonably sized SDU, he’s likely got some social benefits as well. He could have his best friend, his mother, or his grown kid, live with him. This kind of flexibility and informal support could really help as the nation’s population ages. Most people want to stay in their homes as they age, but finances and design can be complicated. An SDU could help aging people meet their needs without moving.
In many localities you can get legal rental income from a permitted SDU, or, if you want, you can live in the SDU and rent out the other dwelling. That should add a lot of flexibility to finances.