Does homeowners insurance cover window replacement when they start rotting at the sills?

Assuming that the damage was the result of natural wear and tear-such as moisture, no. However, if a covered loss, such as a hurricane causing water to enter and the rotting can be traced to that, perhaps. Note, though that the insured has an affirmative duty to ameliorate the damage promptly when found. Therefore, even if otherwise covered, the insurer may take the position that a condition of the policy was breached if the potential for damaged was not mitigated.