Before

After

Mold from Ice Dam in Attic

This exposure shows what happens when water intrusion from ice dam is left untreated for a period of time.  Ice dams are difficult to address or prevent.  A lot of time they actually lift the roof shingle up, and allow for the water intrusion to take place.  Prevention items like gutter heaters or elements or proper snow/ice mitigation is paramount, otherwise roof decking can begin to deteriorate and lead to other issues. Although this is a green or fairly new mold, if left untreated, or mitigated, it can lead to spores that can become more harmful.  White or efflorescence is more common with air molecules rather than physical or visible moisture intrusion.  The reconstruction shows that the damaged roof decking was replaced, and likely resealed.