Is Insulation Mold Resistant? (Explained and Helpful Guide)


As homeowners, we all can relate to how concerned we get when we notice mold has invaded our prized insulation. Considering you must have spent a fortune insulating your home (typically north of $1,500), you wonder if insulation is not mold resistant?

Insulation’s mold resistance depends on its deployed environment and what materials such insulation is made of. Generally, fiberglass insulation excels at resisting mold, especially since it is made from inorganic glass shards that don’t support mold growth. On the other hand, cellulose insulation doesn’t fare well against mold, particularly when sustainably exposed to moisture.

You don’t want to get engulfed in the nightmare of battling insulation mold. A lot has to do with getting your choice of insulation right.

What types of insulation resist mold more, and in what circumstances do they perform best? How do you prevent mold in your insulation, and how can you remove mold if they have already invaded your insulation?

What Type of Insulation is Mold Resistant?

Fiberglass and stone wool have the highest mold and mildew resistance properties among the most commonly used home insulation materials.

Fiberglass excels at resisting mold because it contains significantly reduced glass shards. Being inorganic, glass doesn’t support the growth of mold. Mold is fungus, needing food, oxygen, and water to grow.

Glass doesn’t present any of these nourishments, thereby inhibiting the propagation of mold.

Stone wool also resists mold, especially when deployed on interior walls. Stone wool dries fast and has zero biological components.

Stone wool is essentially melted inorganic rock materials enhanced with recycled slag. This means mold has almost nothing to grow on stone wool – no spores or food.

Generally, when searching for mold-resistant insulation, inspect for the insulation type’s drying capacity, material composition, and moisture resistance.

As you would understand, insulation made from organic materials will likely feed the mold and accelerate its growth.

Similarly, insulation material that absorbs moisture tends to support mold growth. Preferably, go for insulation with hydrophobic capabilities.

Lastly, your chosen insulation should dry out fast when exposed to moisture. The thing is, you can’t be super-confident that water will never permeate your insulation.

Bad things can happen. Your pipes could leak, rain water can penetrate, or the humidity inside your home can unnaturally shoot up.

All of these can dump moisture into your insulation. Now, if your insulation doesn’t quickly dry out, it will surely attract mold.

Are All Insulation Types Mold Resistant?

It is worth stating that not all insulation types do well against mold. While we have established that fiberglass and stone wool excel against mold, other insulation types like cellulose perform don’t perform as highly.

The reason for cellulose insulation’s poor mold resistance is not hard to find. Cellulose is made from ground paper.

Such materials feed mold, especially when wet. When dry, it is hard for mold to penetrate cellulose insulation, specifically those treated with boric acid.

Boric acid remarkably prevents mold in cellulose insulation but dramatically flops once such cellulose insulation becomes wet.

The boric acid would leach out upon exposure to moisture, making the cellulose vulnerable to mold invasion.

What Causes Mold on Insulation?

Moisture is the principal facilitator of mold growth on insulation. When your insulation retains water, and its material decomposes, it is likely to be infested with mold and mildew.

Relative humidity also influences mold growth. In an environment where relative humidity shoots above 50% more (than the exterior), mold thrives.

Even if your insulation material doesn’t decompose, it can yet support mold growth if significant amounts of organic materials nest on it.

Dust on your insulation can also support mold growth.

How Do You Prevent Mold Insulation?

Avoiding moisture accumulation on your insulation is the first step toward keeping mold off. The dryer your insulation stays, the higher your chances of keeping it mold-free.

The location of your insulation determines which specific vulnerabilities (to moisture and, therefore, mold) it has.

For example, if you have insulation in your interior walls, then such insulation risks mold growth if there is a leaky pipe. The same vulnerability extends to insulation on your ceiling.

Therefore, regularly inspecting your pipes against leaks goes a long way in preventing mold growth in such insulation locations.

Insulations in your attic and roof can also gather moisture and attract mold if your shingles get damaged. Keeping your eyes on the structural integrity of your shingles and overall roofing structure also helps.

Lastly, another way to prevent mold insulation is by choosing insulation material with appropriate dimensional stability.

Some insulation materials settle across time. Despite being one of the most ecologically friendly insulation types, cellulose insulation shifts.

Depending on the installation process, your cellulose insulation can settle as much as 20%.

Such shrinkages can create openings for air leakage and moisture penetration, facilitating mold growth. This will even further accelerate the deterioration of the insulation stability.

However, this doesn’t mean cellulose insulation is prohibited. A dense packing installation method, where the material is slightly squished, compensates for such settling.

This avoids mold invasion in the latter part of the insulation’s lifespan.

How to Remove Mold from Insulation?

Having mold on your insulation doesn’t sentence you to completely replacing such insulation (unless it is cardboard or paper insulation).

Except for such exempted insulation types, which are almost impossible to clean, there are restorative procedures to remove the mold and give your insulation a fresh start again.

While the processes vary depending on the porosity of the insulation type, all methods require you to kit yourself against mold before starting.

Fortify yourself with gloves and a respiratory mask. You can either go with latex or rubber gloves.

Alright, next is identifying which insulation has been infested with mold. If porous (say foam insulation or its fabric counterpart), get rid of the mold by scrubbing the insulation with a wire brush.

If the insulation is non-porous, probably it is plastic or fiberglass, you have to rub off the loose mold with a metallic scraper.

It helps if you can completely separate the insulation from the infected area. This way, you can properly disinfect such contaminated regions.

You may use a bleach solution – preferably combined with detergent – on such areas to kill the mold.

Keeping the solution on such areas for about 15 minutes should eradicate the mode.

Also, disinfect the insulation before deploying it. If you can’t use a machine washer, soak the insulation in the bleach solution for about 40-60 minutes.

Follow this disinfection process up by directly drying the insulation in the sun. Sunlight is a potent mold eradicator on its own.

Yes, future mold growths on that revamped insulation are possible. But you can prevent such ugly reoccurrences by spraying your insulation with fungicides.

After this, you can reinstall your insulation.

How Long Does It Take for Mold to Grow on Wet Insulation?

Moisture rapidly attracts mold. Once your insulation soaks and retains water, you can expect mold to start growing on within a day or two.

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