Chapter 3.2
Development Densities

• ALL
• Remove Code Barriers
• Create Incentives
• Fill Regulatory Gaps

Accessory Dwelling Units

INTRODUCTION

Accessory dwelling units (ADUs) help maximize space in residential districts. ADUs are additional living quarters on single-family lots that are independent of the primary dwelling unit and can go by a variety of names such as accessory apartments, second units, in-law units, laneway houses, and granny flats.[1] These additional apartments or cottages may or may not be attached to the existing home and tend to be smaller, with many jurisdictions having size limitations. ADUs are built with fully-equipped living quarters, including kitchens and baths. ADUs are typically owned by the property owner of the single-family lot and are either rented out or granted access to another party depending on the situation and permission pursuant to the local code.[2] While ADUs can take a variety of forms, they generally appear in three configurations in relation to the primary dwelling: internal, attached, and detached. Internal ADUs are integrated into the existing structure, such as a converted attic or basement, attached ADUs are built on as additions to the primary unit, and detached ADUs are built structurally separate, such as a converted detached garage.[3]

ADUs are not a new concept to address affordable housing. In the United States, ADUs were a very popular housing option in the early nineteenth century with the expansion of cities during industrialization.[4] However, following World War II the American shift to suburban-ism led to many leaving the city and seeking out larger single-family lots that were restricted by Euclidean zoning.[5] The rise in housing prices and the decrease in the availability of low-rent units has led many jurisdictions to bring back ADUs as a form of low impact affordable housing. Even outside the legislative process communities have been developing programs using ADUs as a way to combat housing shortages and the subsequent rise in homelessness.[6]

EFFECTS

ADUs respond to the desire to have more small, discreet, affordable, traditional, and environmentally friendly forms of housing.[7] Many people do not require or wish to have the type of large homes that are often mandated in single family districts. Yet, many people also want to enjoy the amenities that accompany these neighborhoods. ADUs not only provide an opportunity to receive rental income and offer multigenerational housing options, but also help maximize space.[8] Further, they do so without changing the essential characteristics of a neighborhood, allowing residents to still retain the benefits of living in the community.[9]

Perhaps most importantly, ADUs help increase a community’s housing supply and offer affordable housing options to many low- and moderate-income residents.[10] ADUs are a way to create affordable housing at low cost because there is no need to develop new infrastructure due to their integration into existing facilities and utilities.[11] ADUs offer an alternative that helps create new housing in low density neighborhoods, while keeping developer and municipality costs comparatively lower.

As a type of infill development, ADUs help increase neighborhood densities to levels where other modes of transit become viable alternatives to automobiles, thus reducing the amount of greenhouse gases being emitted.[12] Also, because ADUs are typically smaller than the average single-family home fewer natural resources are consumed in the construction process as well as the during the day-to-day operation of the unit.[13]

EXAMPLES

Ann Arbor, MI

In 2016, Ann Arbor, MI approved zoning amendments that greatly relaxed the requisite standards for ADUs. The City Council proposed the amendments because of the 2015 Housing Affordability and Economic Equity Analysis which documented increasing housing costs in Ann Arbor.^[14] As a result, moderate income and working families as well as young adults and seniors were being priced out of the housing market.^[15] Previously, ADUs had to be designed so that the appearance of the building remained that of a single-family residence. The amendment altered these requirements such that ADUs can now be designed to match either a single-family residence or a detached accessory building, such as a garage or carriage house.[16] Perhaps the most dramatic change is that of the occupancy requirements. The old ordinance required that ADUs only be occupied by relatives or a maximum of two employees of the homeowner and no rent could be charged.[17] The amendment states that the property owner is required to occupy either the ADU or the main residence, removing the previous restriction.[18] It further prohibits leasing or renting of the ADU for less than 30 days, thus allowing the homeowner to lease to anyone long term.[19]

To view the provision see Ann Arbor, MI Code of Ordinances § 5:10.2 4(d) (2016).

Barnstable, MA

The town of Barnstable, recognizing the essential role accessory apartments were playing in filling the demand for affordable housing, enacted a series of ordinances designed to bring into compliance previously unpermitted accessory apartments as well as providing for the creation of new ones.[20] The amnesty program provides that accessory dwelling units that violate the zoning code ordinances are able to come in compliance provided that they comply with certain criteria. One of these criteria being that upon receipt of a comprehensive permit, the owner of the accessory apartment agrees to rent to a person or family whose income is 80% or less of the area median income.[21] In addition, the rent to be charged cannot exceed the rents established by the Department of Housing and Urban Development for a household whose income is 80% or less of the median income for the area.[22] In order to eligible for the construction of a new accessory apartment, a homeowner must also comply with the previous restrictions.[23] There is also a deed restriction that homeowners of previous and new accessory apartments must execute which will restrict any future rentals by future owners to persons whose income is 80% or less of the median income.[24]

To view the provision see Town of Barnstable, MA Code § 9-12 (2002).

ADDITIONAL EXAMPLES

Town of Lexington, MA Code § 135-6.7 (2014) (permitting ADUs so long as they are located in the principle dwelling, gross floor area does not exceed 1,000 square feet, and there are no more than two bedrooms).

Santa Cruz, CA Municipal Code § 24.16.160 (2016) (waiving development fees for ADUs proposed to be rented at affordable rents).

Bozeman, MT Municipal Code § 38.22.030 (2016) (permitting a single accessory dwelling unit in a detached single-family home or above a detached garage accessory to the single-family home).

Des Moines, WA Municipal Code § 18.55.140 (2014) (permitting one accessory living quarter per residential lot and there must be at least 350 square feet of living space).

Accessory Dwelling Unit Model Code (allowing ADU to be added to a house on any residential zoned lot).

ADDITIONAL RESOURCES

Sage Computing, Inc., Accessory Dwelling Units: Case Study, HUD User (June 2008), https://perma.cc/JLQ6-NEVQ.

Martin J. Brown, Accessory Dwellings: What They Are and Why People Build Them, Accessory Dwellings, https://perma.cc/W4FC-4HUC, (last visited April 19, 2018).

Jonathan Coppage, Accessory Dwelling Units: A Flexible Free-Market Housing Solution, R Street (Mar. 2017), https://perma.cc/CDZ6-L7ZQ.