The answer to 'why is my asphalt shingles leaking' is that there are several common causes, including damaged or missing shingles, improper installation, roof age, and improper ventilation. Symptoms may include water stains on the ceiling, mold growth, and musty odors. Solutions can range from minor repairs to full roof replacement, depending on the extent of the damage.
If the leaks are localized and the damage is minor, you may be able to fix it yourself by replacing a few damaged shingles or sealing any cracks or gaps. However, for more extensive damage or if you're unsure of the root cause, it's best to call in a professional roofing contractor to properly diagnose and repair the issue.