The answer to 'how often to replace skylight' is that the typical lifespan of a skylight is 15-20 years, but this can vary depending on factors like the quality of the skylight, the climate, and how well it's maintained. Skylights are exposed to the elements and can deteriorate over time due to UV damage, weather exposure, and normal wear and tear.
It's generally recommended to inspect your skylight every few years and consider replacement if you notice issues like leaks, cracks, or excessive fogging between the glass panes. Replacing a skylight before major problems occur can help prevent water damage and other costly repairs to your home.