What is an ADU?

The Accessory Dwelling Unit or ADU is an additional self-contained home located either within or adjacent to an existing house. Since it’s on the same lot it can’t be sold separately, unlike a condominium, and the lot must be owner occupied. Building one essentially creates another living unit on a parcel that had previously supported only one. When separated from the existing home the ADU is often referred to as an in-law unit, a backyard cottage, a secondary unit, or a granny flat. The number of terms we’ve invented to describe them suggests their inherent multiplicity of function and it’s this flexibility that’s so attractive! One year it’s a rent generating apartment for a relative; the next year it’s a home office. A detached unit can be a particularly adaptable structure.

ADU benefits:

Rental income for the owner landlord- can offset the mortgage cost and property taxes

Affordable housing size to a renter’s needs- uses existing housing stock more efficiently

Allows extended families to be near one another while maintaining privacy.

Adapts to changing lifestyles and needs such as the home office, a studio, a playroom, or flexible space

Helps to reduce sprawl- it better utilizes fixed municipal resources and expands the range of choices for housing in a developed area

Because the ADU increases the value of the property, local tax rules benefit from increased revenues and a more efficient use of the existing infrastructure- it’s costly to extend public utilities and roads, so it makes good sense to use what’s already in place. Having more members in a community means more local shopping, supporting local businesses.

Most urban and suburban lots are governed by zoning ordinances laws that, among other things, restrict the number of dwellings allowed on a given lot (A dwelling is technically defined as a place for habitation that contains cooking, sleeping, and bathing facilities). By limiting many lots to a single dwelling unit, these municipalities have imposed density restrictions and unwittingly promoted suburban sprawl. Recently however, cities and towns have begun to recognize the need for a more flexible zoning arrangement to meet the needs of their residents and increased housing demands. By relaxing density restrictions and rethinking how we use existing land we can increase housing options in developed areas.

The ADU has been gaining favor in towns and cities with rapidly growing housing demands while the regulations governing the size and configuration of the ADU vary with each municipality. The general limitations are similar- first there are minimum and maximum size limitations that need to be verified with local authorities. The 2015 IRC international residential code allows an accessory dwelling to be as small as 88 square feet but maximums of eight hundred to a thousand square feet are more common and they depend on the existing size of the lot and the type that you’re trying to permit.

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