The answer to 'underlayment damaged' is that the underlayment, which is the protective layer installed between the roof deck and the roof shingles, can become damaged for several reasons. Common causes include exposure to UV light, moisture, and physical damage from foot traffic or falling debris. Symptoms of damaged underlayment may include leaks, mold growth, or visible deterioration of the material.
In many cases, minor underlayment damage can be repaired with a DIY patch or sealant application. However, if the damage is more extensive or the underlayment is reaching the end of its lifespan, it's best to call in a professional roofing contractor to assess the situation and determine if the underlayment needs to be fully replaced.