An accessory dwelling unit (ADU) is a smaller, independent residential dwelling unit located on the same lot as a stand-alone (i.e., detached) single-family home. ADUs go by many different names throughout the U.S., including accessory apartments, secondary suites, and granny flats. [i]

A generic term covering all federal, state or local government programs that reduce the cost of housing for low- and moderate-income residents. This term has the same meaning as subsidized housing.

Housing can be subsidized, or made affordable in numerous ways—giving tenants a rent voucher, helping homebuyers with downpayment assistance, reducing the interest on a mortgage, providing deferred loans to help developers acquire and develop property, giving tax credits to encourage investment in low- and moderate-income housing, authorizing tax-exempt bond authority to finance the housing, providing ongoing assistance to reduce the operating costs of housing and others. Public housing, project-based Section 8, Section 8 vouchers, tax credits, the State Housing Trust Fund, and Seattle Housing Levy programs are all examples of subsidized housing. Subsidized housing can range from apartments for families to senior housing high-rises. Subsidized simply means that rents are reduced because of a particular government program. It has nothing to do with the quality, location or type of housing.[ii]

ARI is a tool intended to identify census tracts throughout Illinois that are becoming less affordable at a faster rate. The ARI uses American Community Survey data to measure change over time across various factors that indicate affordability loss:

• Median Household Income
• Median Home Value
• Families Below the Federal Poverty Level
• Housing Unit Vacancy
• Renter Tenancy
• Individuals Employed in Management, Business, Science and Arts Occupations
• Individuals with a Four-Year Degree (Bachelor’s) or Higher.

Scores in the ARI range from one (1) to five (5). Areas identified by the Index as having significant changes across the above factors (either positive or negative change depending on the factor) will receive higher scores. [iii]

AMI is the midpoint of a specific area's income distribution calculated on an annual basis. It is a key metric used in affordable housing to determine eligibility for federal and local programs and to set income limits and rents. [iv]

The United States Department of Housing and Urban Development (HUD) considers a household to be “cost-burdened” if they spend over 30% of their gross annual income on housing costs. Households that spend over 50% of their gross annual income on housing costs are considered “severely cost-burdened." Households that are cost-burdened are more likely to experience housing instability, which means a household faces housing-related challenges day-to-day at a level that can negatively impact their health and safety.[v]

“Housing that is affordable” refers to any type of housing, regulated or not, that costs less than 30% of a household's pre-tax income. This definition is a generally accepted definition of affordability. This is not to be confused with "affordable housing." [vi]

The term “housing stock” means the number of existing housing units based on data compiled by the United States Bureau of the Census and referable to the same point or period in time. [vii]

Market-rate housing refers to non-subsidized properties that are rented or owned by those who pay market-rate rents or who paid market value to purchase the property. Unlike subsidized affordable housing, market-rate housing does not confer special government benefits. Rents or prices reflect market conditions; these units are typically developed by for-profit developers. [viii]

Middle housing refers to housing that provides diverse housing options along the spectrum of affordability, which includes duplexes, triplexes, fourplexes and bungalows. Middle housing is not eligible for tax credits or most other federal, state or local government subsidies. Typical middle housing types include multiunit structures such as townhomes, duplexes, triplexes and fourplexes. Other examples can include cluster homes and cottage courts. Middle Housing is housing typically affordable to households earning between 80% and 120% of an area's median family income. It is not typically regulated.[i]

Housing that is affordable to low-income households but not regulated or restricted by a funding source, is referred to as “low-cost market rentals.” These housing units are often affordable by nature of their location, condition, age, or the amenities offered nearby or at the property. These units are often called "low-cost market rentals." [ix]

RIAs are targeted geographic areas that demonstrate the most salient market conditions suggesting that revitalization, or concerted community development planning, would be especially beneficial within these communities. RIAs identify census tracts demonstrating one or more of these market conditions, classifying them as either Moderate or High Revitalization Impact Areas:

• Poverty score
• Job score
• Income score
• Vacancy score[x]

A single-family home is a house intended for one family to live in at a time. In most cases, this phrase is used to refer specifically to single-family detached homes—meaning freestanding structures on their own pieces of property and not attached to homes owned by other individuals. [xi]

Supportive housing is a highly effective strategy that combines affordable housing with intensive coordinated services to help people struggling with chronic physical and mental health issues maintain stable housing and receive appropriate health care.[xiv]