What happens if cellulose insulation gets wet?

Author: Odie Fay DDS  |  Last update: Friday, October 10, 2025

When cellulose insulation gets wet, it tends to settle, compacting down into a tighter space within the ceiling, floor or wall cavity. This leaves part of the cavity devoid of insulation, and in the areas that do have insulation, the material is now so dense that it loses a lot of its effectiveness.

What to do if cellulose insulation gets wet?

4-Step Strategy to Overcome Cellulose Insulation Water Damage
  1. Identify and Fix the Source. Immediately address the cause of the water intrusion. ...
  2. Remove the Wet Insulation. Discard all saturated material. ...
  3. Dry the Affected Area. Use fans to quickly remove remaining moisture. ...
  4. Contact a professional.

Is insulation ruined if it gets wet?

While insulation is not automatically ruined if it gets wet, leaving it damp for too long can significantly degrade its performance, reduce its R-value, and promote mold growth.

How long does cellulose insulation take to dry?

How long does it take for the spray applied cellulose to dry? Depending on atmospheric conditions, you should wait 3-5 days after installation before hanging sheetrock. Cellulose dries from the face back towards the sheathing and loses 1/2 it's moisture in the first 24 hrs.

What happens when closed cell insulation gets wet?

Because it doesn't absorb moisture, closed cell spray foam can get wet without losing its insulating properties. Once the water is removed, the foam will continue to perform as expected.

What If My Attic Insulation Gets Wet?

Does mold grow on cellulose insulation?

In addition to losing effectiveness, wet cellulose can also encourage the growth of mold and mildew, contaminate your indoor air with mold spores and lead to structural problems as wood framing begins to rot.

How long does insulation take to dry if it gets wet?

How Long Does It Take Wet Insulation To Dry? The type of insulation, ventilation, temperature, and the humidity all play a role in determining the drying time. Typically, if the insulation does not dry within 2 or 3 days, it is advisable to remove it to prevent mold growth and wood decay.

What are the disadvantages of cellulose insulation?

Cellulose insulation is heavy, and compacts any underlying insulation. Because cellulose insulation is paper, it absorbs moisture when it rains, and in areas of high humidity. Cellulose insulation degrades over time and has to be replaced. Cellulose insulation promotes the growth of mold & mildew in your attic.

What is the life expectancy of cellulose insulation?

Cellulose Insulation

The typical lifespan is 20 to 30 years, with degradation beginning as early as 15 years after installation. As with other types of insulation, severe weather or outside interference can reduce the lifespan. Note: cellulose is often used as supplementary insulation.

Can you put in too much cellulose insulation?

Too much insulation will leave humidity and moisture to accumulate in your attic space. This can lead to mold growth on your walls and insulation. There might also be water damage to the support beams in your home's roof.

Can insulation be left out in the rain?

As commonly known, even the best insulation can be destroyed by water. The same applies to PIR boards. Leaving PIR foam insulation exposed to water for prolonged periods can cause permanent damage. In general, leaving PIR boards under the influence of water for more than 30 days can affect their thermal properties.

How to tell if insulation is damaged?

Signs Of An Insulation Issue
  1. Expensive Energy Bills. If your energy bills have been rising steadily without a change in your consumption, it is typically a sign that your home temperature maintenance system is troubled. ...
  2. Inconsistent Temperatures. ...
  3. Indoor Condensation. ...
  4. Mold Spots. ...
  5. Unwanted Visitors. ...
  6. Ice Dams.

What happens when moisture gets into the insulating materials?

As water has a much higher thermal conductivity than insulation, the absorption of moisture always leads to a rise in the thermal conductivity of the material and a reduction in its insulation performance. In many cases, the damaged insulation is not visible and hence not addressed after the damage is done.

Do you have to replace insulation if it gets wet?

Wet insulation will join its fibers together and create clumps in your attic. If your insulation is compressed or contaminated, then it will lose effectiveness. At that point, you will need to replace the insulation completely.

How do you know if cellulose insulation is bad?

Identifying Old Cellulose Insulation

Over time, cellulose can settle and compact. This changes its original appearance. As it compresses, you may notice areas with uneven coverage. One clear sign of aging insulation is the accumulation of dust and debris.

Is cellulose insulation water resistant?

In addition, because it's susceptible to moisture, blown-in cellulose runs the risk of being wet, and wet insulation will have a drastically lower R-value, which reduces its effectiveness.

Does old cellulose insulation need to be removed?

The bottom line is the old insulation needs to be removed because it hinders the airflow into the attic, it can promote mold growth, and it is dirty. The old insulation on the floor has been exposed to air from the outside because the attic is vented.

Does cellulose insulation lose R-value over time?

However, like other loose fill insulation, it also has a tendency to settle over time, reducing its R-value and its ability to prevent air movement.

Why is cellulose insulation so cheap?

Factors Contributing to Affordable Pricing

Cellulose insulation is primarily made from recycled paper content. The abundance of paper waste provides a cheap and readily available source of raw materials. Additionally, sustainable sourcing practices ensure a continuous supply of cellulose materials.

Do mice hate cellulose insulation?

Cellulose Insulation and Its Composition

As the fire retardant can irritate rodents such as mice, they often avoid nesting within cellulose insulation.

What are the negative effects of cellulose?

Microcrystalline cellulose is generally safe, but some people may experience side effects such as gas, bloating, stomach cramps, and constipation. In rare cases, allergic reactions may occur, manifesting as rash, itching, swelling, severe dizziness, or trouble breathing.

Can cellulose insulation get moldy?

Mold rarely grows in cellulose insulation without direct water damage because of boric acid used as a fire retardant in the material. Boric acid is a natural mold preventer that is very effective at preventing mold growth.

Can mold grow in wet insulation?

Wet insulation can be a dangerous hazard in your home or building. It can lead to the growth of mold and mildew, which can cause respiratory issues for occupants of the building as well as damage to the structure itself.

What happens if insulation gets damp?

When your insulation gets wet, the insulation is not able to repel the heat back into the inside space, and instead, it conducts the energy. This means your insulation is less effective and will result in heat loss. The result? A colder house and higher energy bills.

Can wet insulation be salvaged?

If a large section is affected and the insulation is soaked salvaging the wet insulation probably isn't a viable option. Because it's so absorbent, cellulose insulation retains moisture for a long time making it difficult to dry completely. It also degrades very quickly and won't work well once it gets wet.

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