The answer to 'when to replace roof installation' is that a roof typically needs to be replaced every 20-25 years, depending on the roofing material and local climate conditions. Asphalt shingle roofs generally last 15-20 years, while metal, tile, or slate roofs can last 40-50 years or more with proper maintenance. Signs that it's time to replace your roof include missing, cracked, or curling shingles, leaks in the attic, or significant damage from storms or other weather events.
It's important to have a professional roofing contractor inspect your roof regularly and provide recommendations for repairs or replacement. While some minor roof repairs can be done as a DIY project, it's generally best to hire an experienced roofer for major work to ensure the job is done safely and to code.