The answer to 'how often to replace skylight' is that most skylights should be replaced every 15-20 years. Skylights are exposed to the elements and can deteriorate over time due to UV damage, leaks, and other issues. While some high-quality skylights may last up to 25 years, it's generally recommended to inspect your skylight every 5-10 years and replace it if it's showing signs of wear or leaks.
When replacing a skylight, it's important to choose a durable, energy-efficient model that is properly installed by a professional roofing contractor. This will help ensure the skylight lasts as long as possible and doesn't cause any leaks or other problems in your home.