Mold in Attic Insulation After a Roof Leak
Fiberglass batt and loose-fill insulation both hold water for a long time relative to how quickly they appear dry from the outside, and wet insulation loses most of its R-value while it stays damp. After any roof leak significant enough to wet insulation, the affected sections are usually removed and replaced rather than dried in place, both because drying it fully is unreliable and because it may already be growing mold by the time it is discovered.
Attic mold from a roof leak is also one of the cases most likely to be missed for a long time, since attics are not spaces most people check regularly, and a slow leak can wet insulation gradually over multiple storms before anyone notices a ceiling stain below.
Once the leak is confirmed fixed, replacing the insulation is usually straightforward, but it is worth having the decking above the affected area checked at the same time for any staining or soft spots that would indicate the leak went on longer than expected.
Common questions
Can wet insulation just be dried out with fans instead of replaced?
For a small, recently wet area caught quickly, drying may be attempted, but insulation that has been wet for more than a day or two, or that already shows any discoloration, is generally not worth trying to save given the low cost of replacement compared to the risk.
Does the roof leak itself need to be found before replacing insulation?
Yes, and this is the step most often rushed. Replacing insulation without confirming the leak is actually fixed means the new material gets wet the next time it rains.
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