The answer to 'why is my underlayment cracked' is that the underlayment, the protective layer installed beneath your roof shingles, can crack due to a few common causes. Exposure to UV rays, extreme temperature changes, and improper installation can all lead to cracking and deterioration of the underlayment over time.
Cracked underlayment can allow water to seep through to the roof deck, potentially causing leaks and water damage. It's important to address cracked underlayment promptly to prevent further issues. In some cases, you may be able to repair small cracks, but if the damage is more extensive, it's best to call a professional roofing contractor to assess the situation and determine if the underlayment needs to be replaced.