Do I need a change of use permit if I plan a different business use after buying a commercial building?

Often, yes, and it involves two separate questions that are easy to conflate. First, zoning: municipal zoning by-laws under the Planning Act determine what uses are permitted on a property, so switching from, say, retail to a restaurant or industrial to a different industrial use may require confirming the new use is permitted, or applying for a variance or rezoning if it isn't. Second, the building itself: the Building Code Act, 1992 framework requires a change-of-use permit whenever a building's use changes in a way that affects the code requirements applicable to it, such as fire separation, occupancy load, and accessibility, even if no physical construction is planned.

The mistake buyers make is assuming that because a building already exists and looks suitable, no permit is needed simply to change what happens inside it. A change-of-use permit exists precisely because different uses carry different life-safety requirements, and a building built and approved for one use may need upgrades to safely support another.

Before finalizing plans for a new use, it's worth confirming both zoning permission and change-of-use permit requirements with the municipality early, since either one can affect renovation costs and timing.