Fourplex + Garden Suite: Can You Build 5 Units on 1 Lot?
Double the units, double the fun? Combining a fourplex with a garden suite (detached ADU) can skyrocket your rental yield, but it also creates a regulatory puzzle.
Bill 23 allowed more accessory units, yet local rules still bite. Here are the top tips:
Zoning Limit
Ontario now generally permits up to 4 units per lot, but most cities still cap it there.
- Adding a 5th unit (like a laneway or garden suite behind a fourplex) usually exceeds the density limit
- You’ll likely need a zoning variance or even an official plan amendment — so don’t skip that check
Triple check before proceeding or running your numbers!
Lot Coverage & Size
A garden suite has strict size caps:
- Fire Code limit: Maximum 75 m² (800 sqft) or 90% of the main floor, whichever is smaller (applies to 2–3 bedroom units)
- City bylaws add more rules: local rules may further restrict lot coverage, especially when stacking multiple units. Sometimes unfinished basements count as floor area, thus causing issues with the max area requirement
- Backyard room is tight: double-check yard setbacks and total building coverage before finalizing your design
Separate Systems
Think of the garden suite as its own mini-house:
- Dedicated setup: must have its own address, kitchen, HVAC, and parking space
- Fire safety first requires fire separation from the main home (especially if above grade)
- Plumbing alert: if you’re planning a basement laundry or kitchen, don’t forget a backwater valve
Tags: Fourplex, Garden Suite, Lot Max
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