Arlington Zoning Dictionary

Zoning is complex, based on state laws, town bylaws, and jargon. We prepared this dictionary to help explain terms that may come up in hearings or Town Meeting. Some items below have been adopted from DesegregateCT and other sources.

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General Zoning Terms

As of Right / By Right

“As of right” (or “by right”) means a use or structure is allowed under the town’s Zoning Bylaw, requiring only a building permit. The Building Inspector determines if the project complies with all local zoning and state building codes.

Conservation Land

A tract or patch of land reserved for the protection, development and promotion of natural resources and for the protection of watershed resources, as well as for use as open space or for passive outdoor recreation.

Exclusionary Zoning

Exclusionary zoning refers to restrictions (e.g., dimensional requirements) that seem neutral but increase the cost of housing, thereby limiting the number of low-income and racial-minority people who can live in particular neighborhoods. Such restrictions can end up preserving “enclaves of affluence and social homogeneity,” as a judge noted in an important zoning case.

Special Permit

The town’s Zoning Bylaw allows certain uses and structures if the granting authority (Zoning Board or Redevelopment Board) grants a special permit. Special permits are granted if it is found that any adverse effects of the proposal would not outweigh the benefits to the town or neighborhood. The granting authority must hold a public hearing and frequently imposes conditions to address community concerns and ensure compliance with the bylaw. Special permits are sometimes challenged in court, which can tie them up in expensive litigation for prolonged periods of time.


Under state law, the Zoning Board of Appeals can grant a variance (i.e. an exception) from the requirements of the town’s Zoning Bylaw only if four conditions are met: (1) the project is constrained by unique soil conditions, shape, or topography; (2) literal enforcement of the Zoning Bylaw would cause substantial hardship; and the exception can be granted (3) without substantial detriment to the public good, and (4) without nullifying or substantially derogating from the intent or purpose of the town Zoning Bylaw. All four of these conditions must be met. A variance is essentially permission to deviate from the Zoning Bylaw because requiring compliance would cause unreasonable hardship. It is much more difficult to obtain than a special permit, and many projects that may be attractive from the point of view of public policy will not meet the strict state variance requirements.

Overlay District

An Overlay District is a type of land use zoning district that “lies on top of” an existing zoning district. Overlay Districts provide one of the most flexible means to alter zoning in a town. Builders working in an overlay district can either build to the underlying zoning rules or to the overlay zoning rules. It is common for an Overlay District to provide incentives (e.g., density bonuses) for a builder to build to the new use (e.g., multifamily homes with a larger percentage of affordable housing than usually required).

Zoning Map

Zoning maps, together with the Zoning Bylaw, show the types of uses (such as single family, business, or industrial) that are legal for a particular area of town or for a particular parcel. See here for an interactive zoning map of Arlington.

Uses and Structures


The purpose for which a structure or lot is designed or intended to be used, occupied, or maintained. A few example uses are residential, retail, restaurant, and business/professional/medical office.


A combination of materials for permanent or temporary occupancy or use. A few example structures are buildings, retaining walls, swimming pools, fences, signs, and sheds.

Accessory Dwelling Unit (ADU)

An ADU is a separate, smaller living unit with its own kitchen and bathroom facilities and separate entrance that is attached to or included within a larger residence or located in an accessory structure on the same lot as a larger residence.

Since 2021, Arlington’s zoning bylaw (Section 5.9.2) has allowed ADUs by right for both single and two-family dwelling units. An ADU must be the lesser of 900 sq. ft or half the square footage of the principal dwelling and cannot be built by a developer or used as a short-term rental.

Duplex/Two-Family Dwelling

In Arlington, a single building that contains two homes can be either a “two-family dwelling” or a “duplex.” A two-family dwelling has one home stacked above the other, at least in part. A duplex can be either two homes that are side-by-side or two homes that are front-to-back.


A combination of two or more distinct uses in a single structure, such as a building with retail on the ground floor and housing on the upper floors. Mixed-use development may promote a vibrant, pedestrian-oriented living and working environment. Arlington’s Master Plan prioritizes mixed-use buildings, which are authorized by Arlington’s Zoning Bylaw subject to a Special Permit and Environmental Design Review.

Multifamily housing

Multi-family housing can have different meanings. Under Arlington’s Zoning Bylaw, “multi-family housing” refers to a building containing four or more residences. The State Housing Choice legislation, however, defines “multifamily” (in part) as a building with three or more dwelling units. Note that under state Housing Choice legislation, ADUs do not count towards the number of dwellings in a multi-family building.

Nonconforming Lots/Buildings/Land

A condition that occurs when a lot, building, or land use that legally existed before current zoning requirements does not conform to one or more current requirements, such as dimensional requirements. Most of Arlington’s homes were built prior to the contemporary zoning requirements, and the majority of residential houses or lots are nonconforming in some way.

If someone wants to add to a house or lot that is non-conforming, they may do so provided that no new non-conformities are created and the ZBA determines that the change is not substantially more detrimental to the neighborhood.

Parking Minimum

Parking minimums are local laws that require private businesses and residences to provide off-street parking spaces. In Arlington, most dwelling units (houses, condos, apartments, etc.) are required to have at least one parking space per unit. Before the 2022 Town Meeting, Arlington required more than one parking space per unit in apartment buildings. Cities around the US, ranging from Sacramento and South Bend to Cambridge, MA, have been removing minimum parking requirements entirely.

Arlington Town Boards/Governance

Arlington Redevelopment Board (ARB)

The Arlington Redevelopment Board acts as the town’s planning board and redevelopment authority under state law. It is also the special permit granting authority for projects that require environmental design review. The Town Manager appoints four members of the ARB and the Governor appoints a fifth.

Environmental Design Review (EDR)

EDR is conducted by the town’s Redevelopment Board according to the town Zoning Bylaw (Section 3.4). Its purpose is to provide individual detailed review of uses and structures that have a major impact on the character of the town, and on traffic, utilities, and property values. EDR review applies to development along the town’s main transportation corridors (including Mass Ave, Pleasant St, Broadway, parts of Mystic and Medford Streets, and the Minuteman Bikeway), as well as a few particular uses. EDR standards concern landscape, open space, circulation, drainage, safety, heritage, sustainability, and other criteria.

Residential Design Guidelines

Arlington’s Residential Design Guidelines provide residents, builders, and Arlington's review staff a set of recommendations for new residential construction and renovations. These non-mandatory guidelines apply to low-density residential zoning districts (R0, R1, and R2), which cover the vast majority of Arlington’s land area, but generally enter the review process only for projects needing a variance or special permit.

Town Meeting


Town Meeting is Arlington’s legislative body that deliberates and votes on articles proposed by citizens, committees, and boards. Arlington has a representative Town Meeting, where 12 representatives are elected from each of 21 precincts, making for a legislative body of 252 Town Meeting Members. Arlington’s Annual Town Meeting is generally held beginning in late April. In addition, Special Town Meetings can be called by the Select Board or residents to address interim issues of import.

Zoning Board of Appeals (ZBA)

The town Zoning Board of Appeals decides on zoning variance requests and requests for special permits (if they are not subject to EDR). It also handles comprehensive permits for affordable housing projects under state law Chapter 40B and appeals of zoning decisions by the Building Inspector. The Select Board appoints five members to three-year terms, as well as two associate members.

Massachusetts Laws

Chapter 40A

What we consider “regular zoning” is established under MGL Chapter 40A. This chapter authorizes cities (other than Boston) and towns to establish local zoning rules and sets standards for their administration.

Chapter 40B

Adapted from CHAPA.

Informally known as the “Anti-snob zoning act” at the time of its passage in 1969, Chapter 40B is also known as the Comprehensive Permit Law. It was enacted to expand where low- and moderate-income households can afford to live by reducing regulatory barriers to building affordable housing. In the 2010 state-wide referendum, Arlington voted overwhelmingly in favor (64% to 36%) of preserving 40B in Massachusetts.

Chapter 40B empowers the Zoning Board of Appeals (ZBA) to waive certain town zoning and other requirements for projects where at least 20%-25% of the units have long-term affordability guarantees. In towns where less than 10% of housing or 1.5% of land qualifies for the Massachusetts Subsidized Housing Inventory (SHI), there is a strict review of the 40B decisions by the state and the town has less authority over its decisions. Currently only 6.54% of Arlington’s housing is listed on the SHI, even though the town is close to meeting the 1.5% land area standard.

Housing Choice Legislation

Adapted from MAPC:

Housing Choice refers to a number of changes to the state’s zoning law, MGL Ch. 40A that were enacted in January, 2021 as part of the Economic Development Bond Bill (H.5250). Final guidance for implementing the law was released in 2022.

The law makes major changes to zoning statues in three categories:

  • Elimination of the 2/3 vote for certain zoning changes related to housing production, allowing instead a majority vote to adopt those zoning changes;
  • Multifamily zoning requirements for MBTA municipalities; and
  • Other changes to streamline permitting and discourage meritless legal challenges, including reducing from ⅔ voting for certain special permits to a majority vote instead.
MBTA Community

Under the Housing Choice Law passed in 2021, 175 Massachusetts cities and towns that host or are near an MBTA service are defined as MBTA Communities. Thanks to its proximity to the Red Line at Alewife, Arlington counts as an “adjacent community.” Adjacent communities must have at least one zoning district of reasonable size that allows multi-family housing by right, among other criteria. Arlington will lose eligibility for certain state grants if it is noncompliant.

Affordable Housing

Affordable Housing

As a general term, housing that costs no more than 30% of a household’s gross income is considered ‘affordable’ for that household. For example, a family whose gross income is $120,000 a year should spend no more than $3,000 a month for rent and utilities. Affordable (with a capital A) is housing created in partnership with local and national government agencies such as the U.S. Department of Housing and Urban Development (HUD) and MA Housing and Community Development (DHCD). Affordable housing often has long-term income restrictions and residents have to be selected through a fair housing marketing plan.

Area Median Income (AMI)

Area Median Income is the household income for the median or 'middle' household in a given region. The relevant region for Arlington is Boston-Cambridge-Quincy, MA-NH Hud Metro Fair Market Rent (FMR) Area. Depending on the project, a home may be considered Affordable if it is at 40%, 60%, or 80% of the AMI. It’s important to understand that while some of these numbers look high (e.g., 80% of AMI for a family of 4 is almost $112K) families at and above the AMI cannot afford to rent or buy in Arlington.

Inclusionary Zoning

Inclusionary Zoning is a requirement that sets aside a percentage of units in a multi-family development that are required to be Affordable (e.g., with rent not exceeding a certain percentage of the Area Median Income). In Arlington any project with six or more homes is required to devote 15% of the homes as Affordable.

Dimensional Requirements

Buildable Lot

A lot on which housing can be built given the existing footprint, lot size, setbacks, height, and open space requirements. In contrast, a non-buildable lot is a lot in which some restriction or combinations or restrictions makes building impossible on that particular lot.

Gross Floor Area (GFA)

Gross Floor Area (often abbreviated GFA) is “the sum of the horizontal areas of all stories of a building or buildings measured from the exterior faces of exterior walls, or in the case of a common wall separating two buildings, from the centerline of such common wall”. It’s roughly the interior area of a building, plus the space occupied by the building’s walls.

GFA can include both finished and unfinished interior areas. There are many rules outlining what areas to include and exclude; these rules can be found in Section 5.3.22 of the Zoning Bylaw.

Floor Area Ratio (FAR)

Floor Area Ratio is the gross floor area of buildings on a lot divided by the total area of the lot (GFA/Lot Area). For example, a building with a FAR of 2 could be:

  • a two-story building covering the entire lot,
  • a four-story building covering half the lot, or
  • many other variations with the same gross floor area.

Required distance between building and lot edge.

  • Front yard setback: distance between the building’s front façade and the front lot line, or lot line along the street.
  • Side yard setback: distance between the building and the side lot lines, or the lot lines perpendicular to the street.
  • Rear yard setback is the distance between the building and the rear lot line.
Open Space

Arlington’s zoning bylaw defines two types of open space. First, there are open space districts, which are generally owned by state or town entities, available to the general public, and provide for various conservation and recreation uses. Second there are open space regulations, which apply to the portions of a lot that aren’t occupied by buildings, and not used for parking or vehicular traffic. The formal definition of this kind of open space is “A yard including sidewalks, swimming pools, terraced areas, decks, patios, play courts, and playground facilities; and not devoted to streets, driveways, off-street parking or loading spaces,or other paved areas.” Open space regulations are based on a percentage of gross floor area, so they partially regulate building size and massing, similar to FAR.

The predominant kind of open space required by Arlington’s zoning is Usable Open Space, which must be generally flat, and measure at least 25’ in each direction. This requirement was added to the zoning bylaw in 1975 and a significant number of smaller residential lots do not comply with it.