This article is part of a series on the Strong Towns Strength Test, a simple method to help determine your town's strength and resilience. This series offers step-by-step guides for giving your town the test along with ideas for actions you can take to help your town grow stronger.  We'll publish one article in this series every couple weeks. You can read all our previous Strength Test guides here.


The question we're exploring today is #4 on the Strong Towns Strength Test

In your town, is an owner of a single family home able to get permission to add a small rental unit onto their property without any real hassle?

Adding a small rental unit to a property—typically known as a granny flat or an accessory dwelling unit (ADU)—is a very basic way to increase housing options in a community, provide extra income for a homeowner and allow housing for people of diverse ages, especially seniors or young people.  If your town makes it challenging or impossible to build something like this, you’re missing out on an important opportunity for housing at a time when many cities are struggling with housing affordability issues.

Furthermore, a municipal policy that prevents such a basic thing like the addition of a small rental unit is indicative of other restrictive policies that mandate empty space instead of productive, well-utilized land. One of Strong Towns' key principles is: "Land is the base resource from which community prosperity is built and sustained. It must not be squandered." If your town can’t answer yes to the question above, you’ve got work to do.

How to take the test

1. Start by looking up your municipality’s building and zoning codes. This will take some digging and decoding of language. For instance, many jurisdictions will allow a single-family home to have a shed in the backyard or even a garage converted into an office space. But do they allow for running water in that shed? Is residency in the garage technically permitted? Some of the most common legal hindrances to accessory dwelling units that you'll find in municipal codes include:

  • Lot size requirements – For instance, some communities may allow accessory units but only on large lots. If your town’s typical lot size is smaller than that, you’re out of luck.
  • Utility requirements – Some building codes mandate an entirely new sewer line be built for an ADU instead of allowing it to plug into the main home line. Other codes prevent the use of off-grid systems like composting toilets, which are often easier and more affordable for an ADU than an entire standard sewer system.
  • Occupancy limitations – Many local laws restrict the occupancy of an ADU to either the owner or an immediate family member. Others require that the owner live in the main house, meaning the ADU and primary home could not be rented out at the same time.
  • Parking minimums – They’re inescapable! If a local code requires that off-street parking, let alone covered parking, be provided for an ADU, that often makes them an impossibility because there’s simply not enough space to fit multiple parking spots, a primary home and an ADU on one lot—not to mention the additional cost of building a parking space or garage.
  • Permitting fees – In many municipalities the cost of a permit and other fees associated with construction of an ADU are prohibitively high.

And on top of all of these potential municipal limitations, if you’re in an area with a homeowners association, you’ll likely have to contend with additional restrictions created by the HOA.

Interior of an accessory dwelling unit. (Source: Daniel Ramirez)

Interior of an accessory dwelling unit. (Source: Daniel Ramirez)

2.  Put together a list of the limitations imposed in your town, then ask yourself what, if any, sort of small accessory unit could be built?

3.  Do some research on your town to see whether anyone has attempted to build an ADU. You might even want to undertake some sleuthing to find out whether any exist illegally. 

After you're finished with these steps, take stock and find your answer to the Strength Test question.

An ADU above a garage in Davidson, NC (Source: Brett VA)

An ADU above a garage in Davidson, NC (Source: Brett VA)

Next steps

If you've concluded that building an ADU would be impossible or extremely challenging in your town, here are some steps you can take to change that:

1.   Check out other ADU regulations around the country on this websiteRead the language and learn how it's used to adjust the laws in other municipalities. The movement is gaining steam so there are many examples to learn from.

2.   Gather a coalition of developers, landlords and other neighbors who might be interested in pushing for permission to build ADUs. Discuss what would need to change in your town in order for ADUs to be permitted. Make an action plan for creating this change.

3.   Find key local leaders who would support this effort and work with them to propose new legislation that would allow ADUs. Get support from the people with political power in your community.

4.   Bonus: Attend a workshop to learn more. The Incremental Development Alliance, run by several friends of Strong Towns, is leading the way in training a new generation of small-scale developers. View their event calendar here. The 2017 Build Small, Live Large Summit which focuses on ADU development is also coming up, Nov. 3-5 in Portland, OR. Get more info here.

Towns that get it right

 Here are some towns that offer excellent examples of how to allow and encourage accessory dwelling units.

A primary home with an ADU in back in Portland, OR (Source: AccessoryDwellings.org)

A primary home with an ADU in back in Portland, OR (Source: AccessoryDwellings.org)

Decator, GA

In a shining example of accessory dwelling unit permissions, Strong Towns reader Scott Doyon reports:

Here in Decatur, GA, they're allowable by-right in all R60 and R85 areas, so long as you can remain within the 40% coverage limit. Max 2 bedroom, 800 square feet, owner must occupy one of the two dwellings, no restrictions on rental or to whom. No impact fees. No required parking space. 3' sideyard setback if 1-story; 10' sideyard setback if 2-story.

Read more about Decatur's ADU policies here.

Portland, OR

Strong Towns member, Marcy McInelli, reports that Portland has had a solid ADU ordinance in place for a couple decades now. The result is hundreds of ADUs across the city. See some examples here. A Portland-based blog also offers advice and how-tos for building ADUs in Portland.

The Twin Cities, MN

Minneapolis made headlines nationwide when it approved accessory dwelling units in 2014 after a lengthy political process. Read the ordinance here. Two years later, the neighboring city of St. Paul followed suit. Take a tour of a new ADU in Minneapolis on MinnPost.com.

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Now that you've got the information on how to conduct this test, we want to hear how it goes. Let us know your town's answer to this Strength Test question in the comments, by sharing your photos on social media with the hashtag #StrengthTest, or by emailing us.

A special thanks to the members of the Small Developers/Builders Facebook group for their help on this article. If you're interested in becoming a developer, I highly recommend joining this group.

(Top photo source: Payton Chung)


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