The answer to 'roof decking damaged' is that common causes include water damage, rot, and structural issues. Symptoms may include sagging, soft or spongy spots, and visible damage. Solutions range from minor repairs to full roof deck replacement, depending on the extent of the damage.
If the damage is limited, you may be able to DIY the repairs by replacing small sections of the roof deck. However, for more widespread or severe issues, it's best to call in a professional roofing contractor to properly assess and address the problem. They can ensure the roof deck is structurally sound and prevent further damage to your home.