Under 10 years is generally considered new. Under 5 years is recently replaced. For Ontario home insurance purposes most providers treat roofs under 15 years as low-risk and price premiums accordingly.
The threshold matters most in three situations: buying or selling a home, applying for or renewing insurance, and deciding whether repair or replacement makes more sense. A roof between 10 and 15 years old can still have plenty of serviceable life left if it was installed properly and maintained. But it will come up in real estate disclosure and get closer scrutiny from insurers. Past 20 years most Ontario providers start applying surcharges or coverage restrictions regardless of how the roof looks.
Age thresholds connect directly to whether you should put a new roof over an old one. A roof that insurers are already flagging as old is also the most likely to have underlying decking damage that makes tear-off and inspection non-negotiable. How long a roof lasts in Ontario depends on material and climate exposure. Asphalt shingles under Windsor conditions typically run 20 to 30 years. For full replacement cost context see how much it costs to replace a 2,000 sq ft roof in Ontario.