Glossary

An umbrella term for a secondary, self-contained housing unit located on the same lot as a primary residence. They can take various forms, including backyard houses, garden pavilions, garage conversions, or annexes to the main home. ADUs may be attached to the primary residence (e.g., basement or secondary suites) or detached (e.g., garden suites, laneway houses). They are a cornerstone of gentle density strategies to increase housing availability without drastically changing a neighborhood. 

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• In Ontario, the term Additional Dwelling Unit is often used in provincial legislation and municipal bylaws.
• In Vancouver or parts of the U.S., Accessory Dwelling Unit is the more common term.
• Auxiliary Dwelling Unit is much less common and rarely used in official legislation or policy documents. ‍
• Secondary Dwelling Unit (SDU) is another commonly used synonym in Calgary.

A homeowner or small-scale property owner who actively builds, renovates, or repurposes their property to increase housing availability—either for personal use, family needs, or rental income. Unlike large, for-profit developers, Citizen Developers focus on small-scale housing solutions that support their household or community.

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Citizen Developers contribute to gentle density by:

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• Adding extra housing units on their property, such as ADUs (Accessory Dwelling Units), garden suites, laneway houses, or secondary suites.
• Creating rental housing to generate income and help address affordability in their neighborhoods.
• Supporting multi-generational living, allowing aging parents, adult children, or family members to live together while maintaining independence.
• Converting single-family homes into small multiplexes, such as duplexes, triplexes, or fourplexes, to optimize space and create more housing.

Oversees a building project on behalf of the owner, ensuring it stays on schedule, within budget, and meets quality standards. Unlike a General Contractor (GC), who directly manages construction and takes on financial risk, a CM typically works in a consulting role, advising the owner and coordinating project logistics Key responsibilities include: Planning & Budgeting, Hiring & Oversight, Permits & Compliance, and Risk Management.

A low-rise multi-unit housing type built around a shared courtyard or open space. The units can be arranged side by side (like townhouses) or stacked (like apartments), creating a balance between private living spaces and shared outdoor areas. These buildings are typically 1 to 3.5 stories high, meaning three full floors plus a partial fourth floor, which is often designed as: A mezzanine (an open loft space within a unit), A loft or attic space (used for extra living space or storage) or A setback upper floor (designed to fit under height restrictions).

Low Density: Primarily made up of single-family homes and duplexes on larger lots with more space between buildings. These areas have fewer housing units per lot, limiting housing supply and affordability. Gentle density in low-density areas means adding secondary units like ADUs, basement suites, or laneway houses to create more housing options without major redevelopment.

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Middle Density: Includes townhouses, multiplexes (triplexes, fourplexes), and courtyard apartments, which provide more housing per lot while still maintaining a low-rise, neighborhood-friendly feel. Middle-density housing allows for more affordability and diversity, making it a key part of gentle density initiatives. Unlike high-density areas with large apartment buildings, middle density creates smaller-scale, community-oriented housing solutions.

A single building divided into two separate homes, each with its own entrance, kitchen, bathroom, and living space. The two units can be arranged in two ways: Side-by-side (Units sit next to each other, sharing a common wall) or stacked (one unit is on top of the other, making it ideal for narrower lots in urban areas).

A detached home that contains four separate residential units, each with its own kitchen, bathroom, and living space. The units can have shared or separate entrances from the street. Common layouts include: Side-by-side fourplex and Stacked fourplex.

A self-contained housing unit that can be located above, adjacent to, or within a garage structure. It can be either attached (as in a converted garage) or detached (as a separate structure).

A standalone, detached housing unit located in the backyard of a single-family property. It is designed to be a self-contained unit with its own kitchen, bathroom, and living space.

A construction professional responsible for managing and overseeing a building project from start to finish. Their key duties include: Project Management, Hiring & Managing Subcontractors, Permits & Inspections, Material Procurement, and Auality & Safety Control. Unlike Construction Managers, who typically act as consultants, General Contractors are hands-on, directly managing construction and often taking on financial risk for the project.

The gradual addition of low-rise, multi-unit housing—such as ADUs (Accessory Dwelling Units), garden suites, duplexes, triplexes, and fourplexes—in neighborhoods traditionally made up of single-family homes. The goal is to increase housing supply and variety while maintaining the character of existing communities. Gentle density helps make better use of land by allowing: Additional units on the same property (e.g., laneway houses, basement suites) or the Redevelopment of single-family lots into small multiplexes or infill housing.

The development of new residential units on underutilized or vacant lots within existing urban or suburban neighborhoods. It aims to increase housing density while making use of available infrastructure and amenities, rather than expanding into undeveloped land. Infill housing can take various forms, including ADUs, multiplex conversions, townhouses, and small apartment buildings, and is often promoted as a strategy to address housing shortages, reduce urban sprawl, and create more walkable communities.

A detached housing unit built along a laneway at the rear of a property. It is particularly common in urban areas with laneway access, such as Vancouver and Toronto.

Refers to small-scale housing additions within existing single-family homes or lots, such as basement suites, garage conversions, and garden suites. Unlike Missing Middle, which includes new multiplexes and townhouses, Missing Little focuses on cost-effective, incremental changes that optimize existing structures without full demolition or large-scale construction.

Often synonymous with Gentle Density Housing, refers to a spectrum of low- to mid-density housing types, such as townhouses, ADUs, and multiplexes, that fill the gap between single-family homes and high-rise apartments. This includes small housing or infill development focusing on compact and efficient dwellings that promote sustainability and community integration.

A prefabricated housing unit that can be assembled on-site. Modular units can serve as ADUs or as part of multiplexes. These modules are constructed to meet local building codes and can be configured in various layouts to create a finished building. Modular housing is distinct from traditional construction as it is often faster, more cost-effective, and environmentally friendly due to reduced material waste and controlled manufacturing conditions.

Two to four separate housing units, such as duplexes, triplexes, or fourplexes, within a single structure. Each unit functions as an independent residence with its own kitchen, bathroom, and living space. 

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• The conversion of the principal dwelling into these multiple units, typically ranging from three to five units is called Multiplex Conversion. 
• Unlike Accessory Dwelling Units (ADUs), which are secondary units on the same lot as a primary home, multiplexes consist entirely of primary residences within one building. They are usually owned by a single party but can also include units available for individual sale or rent.

A self-contained unit located within the existing structure of a home, such as in a basement or converted interior space.

Individuals or small firms that undertake real estate development projects on a limited scale, typically focusing on infill housing, ADUs, multiplex conversions, and low- to mid-density residential projects rather than large commercial or high-rise developments.

A term referring to low-density neighborhoods in Toronto and the GTA that are mostly made up of single-family homes and are protected by zoning laws that limit new housing types. These zoning rules restrict higher-density development, making it difficult to build anything other than detached houses. Gentle density initiatives aim to “unlock” the Yellow Belt by allowing more diverse housing options, such as ADUs (Accessory Dwelling Units), garden suites, and multiplexes. This approach helps increase housing supply while keeping neighborhoods livable and community-friendly.

A small to medium-sized attached home where multi-story units are built side by side, sharing one or more walls with neighboring units. Each unit has its own entrance and often includes a private yard or balcony.

A detached home divided into three separate residential units, usually stacked on top of each other. Each unit functions independently, with its own kitchen, bathroom, and living space.