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The ABC’s of ADU’s: 5 Things to Know About Accessory Dwelling Units

Relationships are hard. You think you’ve found “The One” you’ll spend the rest of your life with, but then as time goes on, your wants and needs change. You think it might be time to move on, but you’re willing to offer one more chance … to your house.

After all, if you love where you live, it may make more sense to add on to your property than to buy a bigger house, especially if you need to accommodate changing family dynamics, like an adult child moving back home or aged parents needing a nearby (but independent) living space. This is where an accessory dwelling unit (ADU) can make all the difference.

An ADU is more than just an addition to a house … it’s a fully functioning living area built on an existing home’s property. And as housing costs and property values rise, ADUs can provide an affordable and convenient way to house more people without developing more land.

Intrigued? Then check out these five things you’ll want to know to see if an ADU is right for you.

1. ADUs can be created by repurposing existing space (like converting a basement or garage) or built as a new construction, but however they are made, they share certain characteristics. By definition, ADUs are:

  • Additional units on the property of a primary home
  • Smaller than the primary home
  • Usually created after the main house has been built and occupied

There are several different ways to create an ADU, and each has its own regulations and requirements. Your options will be largely driven by the constraints of your property and your local zoning ordinances.

  • Detached: Construction of a completely separate building on your property
  • Attached: An addition built onto your home
  • Interior Conversion: Remodel of existing space, such as a basement or attic
  • Exterior Conversion: Transformation of an existing shed, garage, or other outbuilding

2. ADUs are living units that function independently of the main home, which means an ADU typically includes:

  • A kitchen and bathroom
  • Living space
  • Its own entrance

Converted interior spaces like basements and attics may or may not have all these features, depending on local ADU requirements.

3. ADUs are growing in popularity across the country, especially in western states. California is now one of the most ADU-friendly states thanks to laws that substantially streamline building requirements and permitting processes. But in most locations, homeowners looking to build ADUs have to navigate a patchwork of state, county, and city regulations, and the permitting process can be daunting. Common restrictions include:

  • Zoning laws
  • Size limits on lots and dwellings
  • Homeowner association (HOA) rules
  • Occupancy, setback, and parking requirements
  • Additional regulations if the space is to be rented out rather than owner-occupied

4. Construction costs for ADUs vary tremendously based on the type and size of the structure, your geographic location, building materials used, labor costs, and permit costs. One firm specializing in ADUs estimates that costs can range from $30,000 (for a garage remodel) to as high as $360,000 (for a brand-new backyard cottage).* When factored against the increased value of your property, however, ADUs may pay off in the long run.

5. For some people, ADUs are the perfect way to maximize the livability of their property, but the cost and complexity of ADU construction mean they’re not for everyone. Before jumping on the ADU bandwagon, you’ll have to consider all the factors involved and decide if this is an option that makes logistical and financial sense for you.

ADU ProsADU Cons
  • Stay in your current neighborhood
  • Create the exact space you need
  • Add to your property's value
  • Additional maintenance, property tax, and utility costs
  • Loss of storage room or parking if you convert an existing basement, attic, or garage
  • Inconvenience and disruption of home life while construction process is underway

*“How Much Value Does an ADU Add?” January 27, 2021, 




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