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Accessory Dwelling Units ADU: Advanced - PowerPoint PPT Presentation

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Accessory Dwelling Units (ADU). Smart Growth / Smart Energy Toolkit. What is an ADU?. An Accessory Dwelling Unit is a secondary housing unit on the same property as a main residence. ADUs are also called accessory apartments, in-law apartments, family apartments, or secondary units.

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Accessory Dwelling Units (ADU)

Smart Growth / Smart Energy Toolkit

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What is an ADU?

  • An Accessory Dwelling Unit is a secondary housing unit on the same property as a main residence.

  • ADUs are also called accessory apartments,

    in-law apartments, family apartments, or secondary units.

  • ADUs are not duplexes :

    • Size of ADU is subsidiary to the main residence

    • Owner of ADU usually lives on the property

  • ADUs are self-contained

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Why consider an ADU bylaw?

  • Shrinking household size

  • Rising real estate costs

  • Aging population

  • Neighborhood stability

  • Character of neighborhoods

  • Environmental benefits

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What does it do for you?

  • Municipality:

    • Increases tax revenue

    • Minimizes subsidies required for affordable units

    • Maximizes use of existing infrastructure and services

    • Keeps growing and aging families together

    • Preserves of existing housing/historic structures

    • Promotes safer and stable neighborhoods

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Who benefits from ADUs?

  • Homeowners – rental income

  • Middle-income tenants – more units

  • Local businesses – employee housing

  • Real estate firms – rental stock

  • Residential contractors – remodeling

  • Lending institutions – home improvement loans

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Affordable ADUs

  • Local Initiative Program can be an instrument for affordability

  • ADU qualification conditions for MA Subsidized Housing Inventory (SHI)

    • Unit approved by local bylaw and DHCD

    • Unit occupied by income-eligible tenant

      (≤80% of area median income)

    • Unit rented at affordable price over term of control

  • For SHI details, contact Department of Housing and Community Development at

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Who typically chooses to build ADUs?

  • Older singles/couples

  • Middle-aged "empty nesters"

  • Younger singles/couples

  • Single working parents

  • People who travel often

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How and where are ADUs built?

  • Apartments in single-family homes

  • Additions to homes

  • Conversion of garages or barns

  • Free-standing cottages

  • Designed into new construction

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ADUs and Neighborhood Type

Traditional Neighborhood Blocks


  • Shallow lots, with or without alley

  • Carriage houses and garages at the back of the lot

  • Original carriage houses small single bay buildings

  • ADUs sited along alley frontage or rear property line

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ADUs and Neighborhood Type

Transitional Neighborhood Blocks


  • Pre-war grid blocks with pre- and post war housing

  • Deep lots

  • Garages located in rear yards

  • ADUs placed within garage zone in rear yards

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ADUs and Neighborhood Type

Suburban Neighborhood Blocks


  • Cul-de-sac blocks

  • Small yards

  • Parking in front of lot with 20’ driveway parking

  • ADUs sited in rear lot areas on bigger lots and/or garage conversions

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Regulation of ADUs

  • Zoning ordinance/bylaw

    • Specifies ADU conversion standards

  • As-of-Right

    • For interior alterations

  • Special Permit

    • For exterior changes and out buildings

  • Licensing

    • Periodic appraisal of ADU via renewal or for change in ownership

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Issues relating to ADUs

  • Eligible tenants

    • Can be restricted to family members, low-income; or unrestricted

  • Maximum persons or bedrooms allowed

    • Varies between 1 to 2 bedrooms with up to 3 people

  • Homes eligible for ADU’s

    • Need for restricting ADU’s to certain percentage?

  • Permitting

    • Special Permit, Site Plan Review or by right

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Issues relating to ADUs

  • Minimum lot size

  • Maximum interior floor space of ADU

  • Setback

  • Ingress/ Egress

  • Wastewater and stormwater management

  • Parking

    • Consider allowing waiver if transit is a reasonable option

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Issues relating to ADUs

  • Recording at the Registry of Deeds/ Land Court

    • Can submit the document to the Building Commissioner prior to issuing an occupancy permit.

  • Annual compliance/ temporary status

    • No requirement for annual compliance/ renewal. Instead, use change in ownership as trigger for renewal of the ADU.

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Launching an ADU program

  • Resident task force

    • Data gathering

    • Community support

  • Sponsoring organization

  • Education for homeowners

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Summary of ADU Benefits

  • Creates new housing using existing infrastructure and services

  • Reduces energy consumption

  • Generates community dollars through home equity

  • Reduces costs for the elderly

  • Preserves housing stock and neighborhood stability

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Selected MA communities with ADU bylaws

  • Case studies

    • Pelham, rural community

    • Lexington, suburban community

    • Northampton, urban community

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Additional Information

  • MA Housing Partnership (MHP)

  • MA Department of Housing and Community Development (DHCD)

  • Background on Subsidized Housing Inventory

  • Older Americans Act

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Additional Information

  • ‘Taking the Initiative – A Guidebook on Creating Local Affordable Housing Strategies’, CHAPA and MHP, Chapter 3, pp. 49-51 (March 2003)

  • ‘Granny Flats Add Flexibility and Affordability’, New Urban News Ithaca, NY, New Urban Publications, (2001)

  • ‘Accessory Apartments’, Leo L. Cram, Missouri Gerontology Institute, University of Missouri (1993)