A substantial change usually means a significant alteration to the nature or accommodation standard of the property, such as adding bedrooms, creating a self-contained unit or carrying out a major extension. Routine repairs, repainting, replacing fittings or ordinary refurbishment will not usually be enough on their own. The landlord should explain the exemption and provide the required information and supporting details when setting the rent. Whether the change qualifies is ultimately determined by the RTB or a court based on the tenancy’s facts, so consider taking professional advice if it is disputed.