What to Do About Wet Insulation

wet insulation

Wet insulation can occur from a number of different sources, mainly depending on the location of the insulation. If it’s installed in the attic, roof leaks are the usual suspect when insulation becomes wet. Wet insulation inside walls, however, may result from leaky plumbing pipes routed through walls or outdoor flooding that has entered the structure. Wherever it occurs, wet insulation requires attention and action, ASAP.

Water affects common types of residential insulation—fiberglass batts and cellulose loose-fill—in two ways:

  • Loss of insulating value. This means the wet material no longer stops heat loss in winter or heat gain in summer.  
  • Wet fiberglass insulation frequently spawns mold growth in the attic

Can Wet Insulation Be Saved?

Two circumstances affect the decision of whether to save or replace waterlogged insulation:

Time Frame

The drying process of wet insulation must be initiated within 48 hours to prevent mold contamination in the material, particularly with fiberglass insulation. If that time frame elapses, replacement of the insulation is the best course.   

Type of Insulation

Fiberglass insulation may be dried in certain circumstances. Continuously directing fans across batts of attic insulation and also keeping a dehumidifier running in the attic may dry wet fiberglass. Alternatively, fiberglass batts may be removed from the attic and dried in a place with better air circulation and warm temperatures.

If fiberglass insulation is installed inside wall cavities, the walls must be opened up or dry air must be injected into the cavities using special drying equipment. The wall cavity and associated wooden structure will typically be wet, too, and must also be properly dried and treated to prevent mold growth.  

Blown-in cellulose insulation is composed of pulverized paper and thus very absorbent. Mounds of cellulose in an attic or inside walls retain moisture for an extended period of time and resist drying methods. In most cases of water damage, except the most minor, replacement of wet cellulose insulation is the best option.

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