The answer to 'why is my underlayment worn out' is that the underlayment, which is the protective layer installed between the roof deck and the shingles, can become worn out over time due to a variety of factors. Common causes include exposure to the elements, improper installation, or simply the natural aging process.
Some common symptoms of a worn-out underlayment include leaks, water stains on the ceiling, or visible deterioration of the underlayment material. If left unaddressed, a worn-out underlayment can lead to more serious problems like rotting roof decking or mold growth. In many cases, the underlayment will need to be replaced to maintain the integrity and protection of the roof system.