Ottawa Secondary Suite vs Garden Suite vs ADU: What’s the Difference?

Why the Terminology Is So Confusing — and Why It Matters

If you’ve spent any time researching additional dwelling units in Ottawa, you’ve probably encountered a bewildering mix of terms: secondary suite, garden suite, ADU, SDU, coach house, in-law suite, laneway house, granny flat, accessory dwelling unit. These terms are often used interchangeably in conversation — but in the context of Ottawa’s zoning by-law, building permits, and Ontario Building Code, they have distinct meanings that affect what you can build, where you can build it, and how it gets permitted.

Getting the terminology right isn’t just academic. Applying for the wrong type of permit, or misunderstanding what your zoning allows, can delay your project by months and cost you real money. This guide cuts through the confusion once and for all.

OGC builds every type of additional dwelling unit in Ottawa — from basement secondary suites to detached garden suites and coach houses. Get a free consultation to discuss which type is right for your property.

The Master Category: Additional Dwelling Unit (ADU)

Let’s start at the top. In Ontario planning law and the province’s More Homes Built Faster Act (2022), the formal umbrella term for any secondary residential unit on a property is an Additional Dwelling Unit (ADU) — also sometimes written as Additional Residential Unit (ARU).

An ADU is defined as a self-contained dwelling unit — with its own kitchen, bathroom, and private entrance — located on the same residential lot as a principal dwelling. It can be attached (inside or structurally connected to the main home) or detached (a completely separate building on the same lot).

Every other term in this guide — secondary suite, garden suite, coach house, in-law suite — is a type of ADU. ADU is the genus; the others are species.

Secondary Suite (Secondary Dwelling Unit / SDU)

In Ottawa’s zoning by-law and building permit framework, a secondary suite (officially called a Secondary Dwelling Unit or SDU) is an additional dwelling unit located within the principal building itself. It is attached — physically part of, or structurally integrated with, the main house.

Common examples of secondary suites:

• Basement apartment: A self-contained unit in the basement of the home, with its own entrance (typically from the side or rear of the house), kitchen, bathroom, and separate heating
• Garage conversion: An attached garage converted into a habitable dwelling unit
• Main-floor side suite: A self-contained unit on the main floor of a bungalow, accessed through a separate entrance
• Upper-floor suite: A unit created from upper-floor space in a two-storey home

Under Ottawa’s current zoning rules, a secondary suite is permitted in any detached, semi-detached, linked-detached, or townhouse dwelling in any zone where that dwelling type is a permitted use, provided the suite cannot change the streetscape character of the road and cannot be severed into a separate property.

Under the new Zoning By-law 2026-50 (expected to take full effect September 2026), the City of Ottawa permits up to four dwelling units on fully serviced residential lots in N1 zones as-of-right — including combinations of secondary suites and detached ADUs.

Garden Suite

A garden suite is a fully self-contained, detached residential unit constructed in the backyard of a lot containing a principal dwelling. It is physically separate from the main home — a standalone building, typically accessed from the rear yard.

In Ottawa, garden suites are permitted on lots that do not have direct access to a public laneway (lots with laneway access use the coach house rules instead — see below). Garden suites are the most common type of new detached ADU being built on Ottawa’s standard residential lots.

Key characteristics of Ottawa garden suites:

• Maximum size: typically up to 80 square metres under current rules (larger suites possible under the 2026 by-law)
• Must connect to the primary home’s existing municipal water and sewer service in urban areas
• Setback requirements apply: typically 1 metre from rear and side lot lines, and minimum separation from the main house
• Must comply with Ontario Building Code requirements for a self-contained dwelling (private entrance, kitchen, bathroom, heating, fire safety)
• A building permit is required before any construction begins
• Exempt from development charges as of 2020

Garden suites are sometimes called backyard suites in common use, and in some Ontario municipalities may also be referred to as garden suites, granny flats, or accessory apartments. In Ottawa, the official City term is garden suite for units on lots without laneway access.

Coach House (Laneway House)

A coach house is Ottawa’s official term for a detached ADU located on a lot that directly abuts a public laneway. Coach houses must be designed to face the laneway and have dedicated access from the lane. They are the laneway-access equivalent of a garden suite.

The City of Ottawa defines a coach house as: a separate dwelling unit that is subsidiary to and located on the same lot as an associated principal dwelling unit, but is contained in its own building that may also contain uses accessory to the principal dwelling.

Key differences between a coach house and a garden suite in Ottawa:

• Access: Coach houses require access from a qualifying public laneway; garden suites access from the rear yard without a laneway
• Eligibility: Not all Ottawa lots are adjacent to public laneways — laneway access is a prerequisite for a coach house that isn’t required for a garden suite
• Design: Coach houses are typically oriented toward the laneway; garden suites are oriented toward the backyard
• Servicing: Both connect to the primary home’s municipal water and sewer in urban areas

In casual conversation, Ottawa homeowners often use “coach house” and “garden suite” interchangeably. Technically they’re different — the laneway access requirement is the distinguishing factor. For a side-by-side comparison, see OGC’s guide: Garden Suite vs Laneway Home in Ottawa.

In-Law Suite / Granny Flat / Nanny Suite

These terms — in-law suite, granny flat, nanny suite, accessory apartment — are informal, colloquial descriptions that do not correspond to a distinct legal or building code category in Ontario. They describe the intended use (accommodating family members) rather than the physical type of the unit.

In regulatory terms, a “granny flat” is simply a secondary suite or garden suite or coach house — depending on whether it’s attached or detached, and where it sits on the lot. The same building code, permitting, and zoning rules apply regardless of whether you intend to house a grandparent, a tenant, or a nanny.

Accessory Dwelling Unit (ADU) vs Secondary Dwelling Unit (SDU): Ottawa’s Specific Terminology

Ottawa uses these two terms with a specific technical distinction that differs from how they’re sometimes used elsewhere in Ontario:

• SDU (Secondary Dwelling Unit): In Ottawa’s framework, an SDU typically refers to an attached unit — within or structurally integrated with the primary building. Basement apartments, internal garage conversions, and main-floor side suites are SDUs.
• ADU (Accessory Dwelling Unit / Additional Dwelling Unit): In Ottawa’s framework, an ADU typically refers to a detached unit — a separate building on the lot. Garden suites and coach houses are ADUs.

This distinction matters for permitting: the building permit application process, setback requirements, servicing rules, and zoning regulations can differ between attached SDUs and detached ADUs. OGC’s guide ADUs vs SDUs in Ottawa goes deeper on the practical differences.

Quick Reference: Ottawa ADU Terminology at a Glance

How Many Units Can You Have on One Ottawa Lot?

Under Ottawa’s current Zoning By-law (2008-250), a fully serviced lot can have up to three total dwelling units: the principal dwelling plus either two SDUs within the home, or one SDU within the home plus one detached ADU (garden suite or coach house).

Under the new Zoning By-law 2026-50 (expected September 2026), fully serviced lots in N1 residential zones can have up to four units as-of-right, opening up more combinations of attached and detached units on a single property.

Note that only one detached ADU is permitted per lot under current rules — you can’t build both a garden suite and a coach house on the same property.

Which Type Is Right for Your Property?

The right type of unit depends on your lot, your goals, and your budget:

• Basement already exists or can be finished? A secondary suite / SDU is often the most cost-effective starting point.
• Want to maximize privacy and rental independence? A detached garden suite or coach house commands premium rent and offers complete separation from your living space.
• Lot abuts a public laneway? A coach house may be the right detached option — and may have design advantages from the laneway-facing orientation.
• Planning for multi-generational living? Either an attached SDU or a detached garden suite works well — the choice depends on the degree of privacy and independence the family arrangement requires.
• Maximizing income potential? A detached ADU generates the highest long-term rental income due to complete privacy and independence.

OGC builds all types of secondary units across Ottawa — from basement secondary suites to full detached garden suites and coach houses. Our team will assess your property, confirm what’s permitted under your current zoning, and design a unit that works for your lot and your goals.

Explore Your Options With OGC

• Explore OGC’s Custom Home and ADU Building Services
• ADUs vs SDUs in Ottawa: Understand the Difference
• Garden Suite vs Laneway Home in Ottawa
• How to Rent Out Your Backyard Suite in Ottawa Legally
• Can You Airbnb a Backyard Suite in Ottawa?
• Connecting Utilities to Your Backyard Suite in Ottawa
• Request a Free Property Assessment

Related reading: Ottawa’s New Zoning By-Laws | How to Get a Building Permit in Ottawa | Ottawa N1 Zoning Rules