The answer to 'why is my underlayment worn out' is that the underlayment, a protective layer installed beneath the roof shingles, can become worn out over time due to exposure to the elements and normal wear and tear. Some common causes include UV radiation from the sun, moisture infiltration, and physical damage from high winds or falling debris.
Symptoms of a worn underlayment may include visible cracks, holes, or deterioration of the material. This can lead to leaks, water damage, and other roofing problems if left unaddressed. In most cases, the underlayment should be replaced every 10-20 years, or sooner if significant damage is observed.