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Efficiency and Affordability: Accessory Dwelling Units (ADUs)

I haven't been posting often lately, as things have been pretty hectic.   I did receive a question the other day about  topic that I haven't spoken about here:  Accessory Dwelling Units (ADUs), and it inspired me to write a quick post.  These are sometimes known as "accessory apartments," "mother-in-law suites" or "granny flats" - they are ways to provide more housing options in existing neighborhoods by allowing homeowners to build additional units on their lots.  ADU is a catch-all term for all of these situations - either units attached to existing homes or placed somewhere else on the property, say over a garage or a stand-alone in the backyard. 

AARP and HUD publications on ADUs
(Links to originals within post)
They are part of the range of housing options that help to ensure that people of all ages, including older adults, can meet their needs.  AARP's model ordinance on ADUs was written by staff at the American Planning Association and was an attempt to find a set of regulations that would meet livability goals.  Although this is an older publication, it does a good job of providing a foundation for creating a successful ADU program.  When done well, ADUs have advantages - one can provide a place for a "mother-in-law" or other relative to stay close to loved ones.  For an older person with declining incomes and growing housing affordability challenges, renting out a unit or moving a friend or relative onto your property can help with those costs (see Housing's Back, or Is It? for more on affordability challenges facing the 50+ population).  You can read more about AARP's housing philosophy and the related public policies at (Chapter 9) -  AARP's policy  expressly says that states and localities should look to the  model act to create legislation to support ADUs. 

For any town, city or county considering a plan to broaden the implementation of ADUs, it’s important to anticipate the fears of residents and local officials (added traffic, parking problems, poor conditions, etc.)  One that's done, it's time to do some research - look at the regulations that have been put in place elsewhere.  The good examples will address those concerns while maximizing the freedom of property owners and providing another source of housing options. I’m a fan of a study on ADUs that HUD did - it's a collection of case studies of places that have implemented ADUs.  The case study approach is great - it allows us to look at how each jurisdiction dealt with the pros and cons of this  type.

Many articles have been written about the successful ADU program in Santa Cruz,California, but several other places have implemented ADU programs over the years.  One thing that I have learned as an observer of these efforts is that the story of each effort is different because locations and people are different.  This is an area where a one-size-fits-all policy will not work - the program (if feasible) must be tailored to that particular community.  When the District of Columbia and Montgomery County, MD looked to expand the use of ADUs in the Washington region last year, there was great pushback from residents who feared overcrowding and a general decline of conditions -  sometimes stated (and I suspect more often felt) was a fear of low-income people moving into these apartments and causing problems for neighbors.  

These fears usually predate an ADU program - other conditions in the community or  perceptions of conditions in the community create these concerns.   This is a prime example of an occasion when policy becomes political - this is a change that is literally in one's own back yard, and opinions can be strong .  The planner or politician who goes into a community meeting on this issue must do their homework first and know what to expect.  Concerns about parking, fire safety and or about the condition of neighborhoods should be anticipated and provisions will need to made to address concerns. Those concerns also need to be weighed against the need for housing options in the community and the property rights of landowners who want flexibility with their property. The reward for the community that implements ADUs successfully is a range of new housing options, and in places where housing affordability or the opportunities to age-in-place are limited, this can positively impact many families. 

Do you have any thoughts on ADUs?  Have they been implemented in your town?  What should a town that's considering ADUs think about?  Share by leaving a comment below or @DrUrbanPolicy. 


  1. No question that fears predate the ADU program. Even in places that have "successful" or "aggressive" programs, there are very few legal ADUs compared to the number of single family residences--- so ADUs are generally not that visible, and there is not much basis to evaluate community effects for good or for bad.

    Opponents may be reacting to experience in places with rampant illegal ADUs, or they may have the basic attachment that anyone has to their neighborhood -- they don't want it to change. "Renters" can be a specter -- even though most homeowners were renters themselves once.

    The way the subject is presented does seem to make a difference. Most people are uncomfortable with the bureaucratic notion of 'accessory dwellings' and 'affordable housing,' but they are completely at home with building a little house on the alley for grandma.

    Big homebuilders in the Southwest are selling something called "multigenerational houses." These are simply houses with internal ADUs, but they never use words like "ADU." The marketing focuses on the family connections such places can support, instead of the rental aspect.

    But at some point those ADUs will be rented out to strangers -- that's just the way housing stock works. And my guess is that neighborhoods will be fine with it.

  2. ADUs can support generational and extended family strategies for empowered aging in place. Say yes to multigenerational homes!


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