Does Wet Insulation Need to be Replaced?

Estimated reading time: 5 minutes

There are many causes for wet insulation, like attic insulation that gets wet from a leaking roof. That leads many to ask, does wet insulation need to be replaced? Suppose you live in a humid area. That humidity is beneficial when you want plants to grow, but it could lead to other issues. Like, what happens when that moisture gets inside your home? The short answer is that it can damage your insulation.

How Water and Moisture Affect Residential Insulation

The two most common types of residential home insulation include cellulose loose-fill and fiberglass batts. While these two types of insulation differ from each other, water affects them in the same way.

Cellulose Loose-Fill Insulation

If you see loose, gray fibers in your attic or crawlspace, that means your home has cellulose loose-fill insulation. Many choose cellulose loose-fill insulation because of its insulating properties and because it’s an eco-friendly option.

loose cellulose

Because this type of insulation features plant fibers, that means it can pick up moisture like a sponge. If a small section of the insulation is wet, you might be able to get away with replacing only the affected area. It might also be possible to dry it out.

For example, this might be possible if you have a significant amount of space to dry out the insulation. You’ll need to lay the bats out to dry for ten days or longer. If you can remove the insulation to dry it out, you’ll need to clean and dry the area thoroughly where the water leak is. That way, you’re preventing mold or mildew growth in that area.

However, if the water leak is significant, don’t be surprised if most of the insulation soaks it up in the affected area. The cellulose construction of this insulation is the ideal environment for breeding mold and mildew. That’s unfortunate as it can grow mold or mildew throughout a few days instead of taking several weeks. In that case, you’ll need to replace the entire section of insulation.

Fiberglass Batts

If you see pink loose-fill or batting, that means your home has fiberglass insulation. Because fiberglass batts feature spun glass fibers, they won’t absorb water. If water does get into this insulation, it won’t cause a significant amount of damage. However, if a water leak causes this insulation to get wet, you can expect that issue to dramatically reduce the insulation’s functionality.

Water is a natural temperature conductor. That means if warm air tries pressing against wet insulation, the water transfers warm air outside your home. The fiberglass’s density also makes it challenging for water evaporation to occur. However, this is typically only the case when the insulation is thoroughly wet.

In the case of thoroughly drenched fiberglass batts, the recommendation is to replace it all. Otherwise, you run the risk of the wood surrounding the insulation experiencing damage. If the insulation isn’t too wet, you can use a few fans or a dehumidifier to dry it out. If that doesn’t do the trick, remove the batts and place them in direct sunlight or a warm area to dry.

Circumstances Dictating if You Can Save Insulation

Remember that it isn’t uncommon for wet insulation to spawn mold and mildew growth. So, keep that issue in mind when determining if you should save it or if it needs replacing. Two circumstances dictate whether you can save wet insulation or not.

Insulation Type

Under some circumstances, you can dry cellulose, loose-fill insulation, and fiberglass batts. For example, if you’re trying to dry out fiberglass batts, you’ll achieve the best results by aiming fans at the wet insulation. It’s also a good idea to keep dehumidifiers running in the affected area, like your attic or crawlspace.

If you have cellulose loose-fill insulation, that’s typically comprised of very absorbent pulverized paper. That means the insulation inside your walls or in your attic can retain moisture for extended timeframes. Unfortunately, that also means this insulation type typically resists drying methods. Unless it’s a small area, the recommended mitigation is removing and replacing this insulation type.


Can you determine approximately when the leak occurred? If you can’t make this determination, the recommendation is to replace the insulation wherever you feel or see evidence of moisture. If you find the water leak immediately, you have 48 hours to mitigate the situation. Otherwise, controlling or preventing mold or mildew growth won’t be easy. You’ll find this is especially true if you have fiberglass batting.

Does Wet Insulation Need to be Replaced in Wall Cavities?

Your attic or basement aren’t the only areas where water leaks can occur. Holes in siding or other damage can cause water leaks to occur inside your home’s wall cavities.

fiberglass insulation

The only way to dry out wet insulation inside wall cavities is to open up the wall. Then, you’ll need to inject dry air directly into the wall’s cavities using special drying equipment. Remember that the wooden structure surrounding it will also be wet when you have wet insulation. So, to prevent mold and mildew growth, this is the recommended mitigation.

You can take several steps to prevent wet insulation from happening again after drying out or replacing sections. Those include:

  • Checking your roof frequently to ensure it isn’t leaking.
  • Preventing moisture from seeping in by inspecting your siding for holes
  • Sealing your basement and foundation walls to prevent moisture from intruding.

Address Wet Insulation Immediately

While your first reaction might replace wet insulation as soon as you find a leak, it might be possible to dry it out if the leak isn’t significant. However, if the insulation is too wet, that causes its fibers to join and create wet clumps in your attic, crawlspace, and other affected areas.

If compression or contamination occurs, then your insulation loses its effectiveness. Then, the recommendation is to contact an insulation specialist to replace it immediately.

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