We bought a house with an attic fan that was improperly installed. During a pounding rain storm water poured thru holes around the fan, across the ceiling joists, thru a heat duct and stained the ceiling below. The blown-in insulation also got wet. We put fans in the attic, dried out the insulation and repainted the ceiling. However, I am having a debate with my husband on whether or not we need to replace the ceiling insulation. I have a 3 and 6 year old with allergies and am concerned about the dangers of mold.
lta1atl - 10/13/06 10:50 AM
Mold needs air, water and an organic food source to prosper. Insulation is inorganic so it is not a mold food. However, I have seen cases where mold CAN grow in insulation.
Some years ago I was filming a story about a "sick house" for a national television program. Upon entering the attic to film the lack of adequate ventilation there, I had a very hard time doing my segment without getting out of breath. Thinking that I needed to lay off the cookies and get my tail to the gym more often, I pushed on and got through the segment. Before stepping out of the attic though, I grabbed a small handful of the insulation on a hunch to send to the lab to check for mold.
Several days later, I got a call from the lab  with a positive result. For the first time anywhere in America, I had inadvertently discovered that mold CAN grow in inorganic fiberglass insulation - given the right set of circumstances, that is. In this case, we were dealing with a very damp/humid home. Secondly, the ceiling of the home had many high-hat (flush mounted) lighting fixtures. As a result, dirty, damp and dusty air was leaking up through the light fixtures and on up into the insulation. The insulation acted as a "filter" and trapped the ORGANIC dust. Fueled by the excessive humidity, mold grew in the dust being trapped in the insulation.
So, while inorganic insulation itself won't sustain mold growth, organic dust trapped in the insulation will. When we looked at the slides of the mold under the microscope, we saw mold wrapped around the fiberglass strands like ivy on a tree trunk (see photo above). It was a most amazing find.
Now, in your case, assuming the home was just saturated once and dried quickly, there is probably little risk that you have a mold problem. However, having said that, insulation is cheap and if it will make you feel better, simply remove and replace it.