Frost shows up in the attic when moisture-laden air from the house gets into the attic. ... When the moisture gets into the attic, it condenses on the roof sheathing, attic insulation and roof trusses in the form of frost. The frost itself doesn't do any damage, but once it melts things get wet, which is when the damage occurs. This can also cause mold.

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The images are from a new home that was purchased directly from the builder. They did not have this home inspected until they realized they had some major defects and had to go through a tremendous amount of stress and frustration trying to get things repaired from the builder.