The legal framework for residential density in Markham has changed fundamentally. Ontario Regulation 462/24, in force since 2024, empowers homeowners to add more secondary suites than previously permitted — and the City of Markham is actively updating its Official Plan and zoning by-laws to allow up to three Additional Residential Units (ARUs) on most residential lots, meaning up to four dwelling units total on a single property. For Markham homeowners who want to maximize the income-generating potential of their existing property, this change opens options that simply did not exist two years ago. Michael John Lau, top real estate agent in Markham Ontario, guides homeowners through the permit process.

What Three Units on One Markham Property Actually Means

Under Markham’s evolving policy framework aligned with the province’s Housing Accelerator Fund Action Plan, a typical Markham detached home could potentially contain:

• Unit 1: The primary dwelling — the existing home, used by the owner or rented to a tenant
• Unit 2: A legal secondary suite within the existing footprint — a basement apartment with its own entrance, kitchen, bathroom, and bedroom
• Unit 3: A garden suite in the rear yard (detached residential structure) — or a coach house above a rear-lane garage (particularly relevant in Cornell) — or an additional interior suite where the house configuration permits it

Step 1 — Confirm Your Property’s Current Eligibility

Before constructing any secondary suite in Markham, homeowners must contact Building Standards at 905-475-4870 to determine if they are allowed in their specific area. While the province has directed municipalities to permit up to three ARUs on most residential lots, Markham’s implementing zoning by-law amendments are in progress. Some areas are fully enabled. Others are still transitioning. Heritage district properties may have additional restrictions. Call Building Standards and ask specifically about your address before investing in design drawings or contractor commitments.

Step 2 — Understand What Each Unit Type Requires

Basement Secondary Suite (Unit 2): Minimum 1.95 metre ceiling height throughout, separate entrance, 45-minute fire-rated separation from the main dwelling, egress windows in all bedrooms, interconnected smoke and CO alarms, ventilation, heating, and a kitchen and bathroom with dedicated plumbing. Full Ontario Building Code compliance required.

Garden Suite (Unit 3): A detached residential structure on the same lot. Requires its own building permit addressing foundations, structure, energy efficiency to current code, fire separation from property lines, and all mechanical systems. Minimum lot dimensions apply — typically 1.2 metres from property lines. Most Markham detached home lots of 40 feet width or more can accommodate a modest garden suite. Box Grove, Markham Village, and Bullock lots with 50+ foot frontages have the most flexibility.

Coach House (Unit 3 in Cornell): Available primarily in Cornell, where rear-lane access and original community design included coach house provisions. Applications follow the housing permit process through ePLAN with specific drawings showing the coach house unit and its relationship to the garage below and the main dwelling.

Step 3 — Prepare the ePLAN Drawing Package

All Markham building permit applications for secondary suites and garden suites are submitted through the ePLAN digital portal. Paper applications are not accepted. Required drawings typically include: a site plan showing all units, their footprints, setbacks, entrances, and parking; floor plans of each unit with room names, dimensions, and ceiling heights; construction details for fire separation; window schedule confirming egress compliance; smoke alarm and CO alarm interconnection diagram; plumbing and mechanical system details; and energy efficiency documentation for new structures. Engage an architect or designer familiar with Markham’s specific ePLAN formatting requirements before submitting — non-compliant submissions are rejected at pre-screen.

Step 4 — ESA Inspection, Fire Inspection, and Registration

After construction, an ESA (Electrical Safety Authority) inspection certifies the electrical system in each new unit. After ESA certification and City building inspection, the home must be registered as a multi-unit dwelling with the City Clerk’s Department. A Two-Unit or Three-Unit House Declaration Form must be submitted with the registration fee. Fire inspection by Markham Fire and Emergency Services at 905-415-7521 is required before registration is complete.

The Investment Case for Three-Unit Conversion in Markham

At today’s interest rates, the Canada Secondary Suite Loan Program’s $80,000 loan at 2% over 15 years costs approximately $515 per month to service. Against $4,000 to $5,200 per month in combined rental income, the net rental cash flow after loan servicing is approximately $3,485 to $4,685 per month. The capital investment in a garden suite — typically $150,000 to $250,000 — is recoverable in four to seven years from rental income alone.