The answer to 'when to replace shingles' is that you should typically replace your roof's shingles every 15-20 years, or when they show signs of significant wear and tear. Shingles can become cracked, curled, or missing over time, and this can lead to leaks and damage to your home's interior. It's important to inspect your roof regularly and replace the shingles before they cause any major problems.
The lifespan of your shingles can vary depending on the quality of the materials, the climate in your area, and how well the roof has been maintained. Asphalt shingles, which are the most common type, typically last 15-20 years, while more durable materials like metal or tile can last 40-50 years or more. If you're unsure about the condition of your roof, it's best to have a professional roofing contractor inspect it to determine if replacement is needed.