You are correct. The faulty workmanship exclusion does not apply. That exclusion only applies when another excluded event occurs to cause the loss. For example: say that the roof was constructed poorly. As a result, birds got into the attic, nested there for some time, and caused damage. The HO 00 03 excludes damage done by birds.

Without the faulty, inadequate, or defective construction exclusion discussed above, the insured could then claim that his loss was caused not by the birds, but by the use of those faulty methods.

That is the purpose of this exclusion. But, because a covered ensuing loss—ice and snow damage—has intervened, the exclusion does not apply.

The insurer also may not apply the wear and tear exclusion to deny coverage for the roof. If the roof was worn out, a covered loss still happened. The wear and tear exclusion is meant to preclude coverage for normal wearing out or deterioration that occurs over time. The wear and tear exclusion prevents insureds from expecting insurers to replace worn out property. But once a covered loss happens—in this case the ice and snow damage—that exclusion doesn't apply, either.

Both the insured's roof and interior are covered by the HO 00 03 for this loss.