Cities call them accessory dwelling units. Most of us know them by other names-including cottages and mother-in-law units. Whatever name you might know them by, these living spaces typically include their own living space, kitchenette, and bathroom, and either share a wall with the main house or are detached, usually situated in a backyard. And they are growing in popularity as municipalities are increasingly seeing them as a way to answer a variety of issues. Some of their benefits, according to the Municipal Research and Services Center of Washington include:


ADU's increase the supply of affordable housing
Satisfy a growing need for smaller housing
Make efficient use of existing housing stocks and infrastructure
Provide homeowners with extra income
Make it possible for adult children to provide care and support to a parent in a semi-independent living arrangement
Can help first-time buyers qualify for loans and help offset mortgage payments

Many municipalities in the South Sound currently allow attached ADU's, detached ADU's, or both. Tacoma allows attached ADU's in almost all of their zoning areas, and detached ADU's in some of their residential zones, while unincorporated Pierce County allows both attached and detached ADU's in nearly the entire county.