Can Water-Damaged Insulation Be Salvaged?

wet insulationInsulation in the attic is often the first victim when roof leaks occur or when plumbing pipes routed through the attic leak. The two most common types of insulation — fiberglass batts and blown-in cellulose loose-fill—are vulnerable to attic water damage in two specific ways:

Loss of insulating value. Wet insulation no longer performs its primary function of inhibiting heat transfer. Saturated insulation typically loses at least 40% of its insulating R-value. While fiberglass is technically waterproof, inside an enclosed attic the thick batt retains moisture which degrades its thermal resistance properties. Cellulose loose-fill, made of pulverized particles of paper and cloth, absorbs a large volume of water and compacts, losing the fluffy characteristics that make it an effective insulator.

Mold growth. Fiberglass insulation traps dust, which typically contains microscopic airborne mold spores. Following exposure to moisture from attic leaks, active mold growth affecting the paper backing of fiberglass batts is common. Cellulose insulation is treated with chemical fire-retardants that also make the material itself fairly mold-resistant. However, the absorbency of cellulose means destructive mold is still a major factor if it becomes wet. Saturated cellulose insulation acts like a wet sponge that continuously transfers moisture to adjacent wooden structure in the attic and to the ceiling drywall below, causing mold growth and destructive decay in these materials.

Can Wet Insulation Be Saved?

  • Fiberglass batts will eventually dry if lifted up and exposed to warmth and sustained air circulation. However, if active mold growth is evident, the material should be removed. Drying a large area of soaked insulation as well as detecting mold is a labor-intensive process. Because fiberglass batts are relatively low-cost, instead of attempting to salvage wet, possibly contaminated material the better option may be removal and replacement with new insulation.
  • Soaked cellulose insulation will retain absorbed water for an extended time and resists drying. During that time, it will also degrade wooden structure and trigger attic mold growth. Wet cellulose is generally not salvageable and needs to be removed, then new material blown-in to replace it.


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