Most roofs last 20 to 30 years, but you don't need to wait for a leak to start thinking about it. If shingles are curling, cracking, or losing granules, that's a clear sign. Also check for missing pieces, dark streaks that might be algae, or daylight peeking through the attic. After big storms, look for damage, especially around vents and chimneys. Sagging spots or water stains on ceilings mean trouble. If you're patching more than once, it's probably time for a full replacement rather than ano… when to replace a roof 17