The answer to 'why is my asphalt shingles sagging' is that the shingles are likely experiencing structural issues or improper installation. Asphalt shingles can sag due to factors like inadequate roof ventilation, excessive weight from debris or snow buildup, or poor quality materials. This can lead to leaks, mold, and further damage to your roof.
If you notice sagging shingles, it's important to address the issue promptly. Trying to fix it yourself may be possible for minor cases, but it's generally best to call a professional roofing contractor to properly diagnose and repair the problem. They can assess the root cause and recommend the best solution, whether that's replacing damaged shingles, improving ventilation, or a more extensive roof repair.