Zoning and permits come before design
Whether a secondary suite is permitted, and under what conditions — as an addition, a basement conversion, or a separate structure like a laneway or garden suite — depends on the specific municipality's zoning bylaws, which vary considerably across Ontario and have been shifting in recent years as many municipalities loosen restrictions to support this kind of housing. Confirming what's actually allowed on the specific property, before spending money on design work, avoids paying for plans that don't match what's permitted.
A building permit is generally required regardless of the exact form the suite takes, and inspections along the way confirm the work meets code — this isn't optional for a legal, insurable secondary suite, even though informal conversions without permits do happen.
Why doing this properly, not informally, matters more with an aging parent
An unpermitted conversion carries real risk beyond legal exposure — insurance can be affected if a claim arises in an area that wasn't properly permitted and inspected, and safety features like proper egress, smoke detection, and electrical work matter more, not less, when the occupant is someone with mobility or health considerations. This is a case where cutting corners to save time or money creates exactly the kind of risk the project exists to reduce.
Accessibility features — a no-step entry, wider doorways, a main-floor layout without stairs — are worth building in from the start if the suite is specifically for an aging parent, since retrofitting later is more disruptive and expensive than planning for it in the original design.
Weighing it against the alternative options
A secondary suite is a real investment of time and money, and it's worth comparing honestly against other paths — moving a parent into an existing bedroom with some modifications, in-home care without construction, or a different living arrangement entirely. It tends to make the most sense when the family expects the arrangement to be long-term and values the added privacy and independence a separate suite provides over a shared living space.