Fiberglass Insulation Being Installed in Wall / dpproductions

Reliable insulation is essential for keeping your home comfortable affordably. While insulation can last for decades, it can also fail early due to water damage, pests, and other issues. Knowing what to expect from your insulation helps you maximize its lifespan and decide when it’s time for replacement.

Estimating Your Insulation’s Lifespan

Blow Fiberglass Installation in Attic / photovs

How long insulation lasts depends on the type and how well it’s maintained. The International Association of Certified Home Inspectors states many common types of insulation, including cellulose and fiberglass in batt and blown-in form, rockwool, and foam board, can last 100 years or more. While this might be true technically, it only happens under ideal conditions.

Because conditions in the average home are rarely ideal for keeping insulation pristine, insulation often fails before reaching its maximum lifespan. For batt and blown-in insulation, warranties range from 10 to 70 years, but on average, most should last at least 25 years, barring any serious issues such as flooding. Natural insulation materials, such as straw and wool, also last several decades under average conditions.

Without good home maintenance, insulation can start to degrade within as little as 15 years. Even if you keep your insulation mostly free from damage for 50 years or more, it won’t be as efficient as when it was new. For that reason, some experts recommend replacing your insulation after 25 years to make sure you’re getting optimal efficiency.

Choosing Durable Insulation

Worker Installing Rock Wool Insulation in Wall / Bilanol

Although most common types of insulation have around the same lifespan, there are some differences between them.

Fiberglass insulation doesn’t rot or grow mold, but the paper backing can. It’s also non-flammable, except for the backing. The biggest drawback of fiberglass is that when exposed to high moisture levels, it compresses and sags, causing it to lose R-value (thermal resistance) so that it’s less effective. Blown-in is more susceptible to moisture problems than batt form. Rodents and insects love using fiberglass for nests, which puts it at further risk of damage.

Cellulose insulation is made from recycled paper treated to stave off mold, decay, and pests. Although it can still develop these problems, it holds less moisture than fiberglass. Because it’s denser than fiberglass, it doesn’t compress as easily, so it retains its R-value for longer. The downside of cellulose is that it’s more expensive and difficult to install by yourself.

Mineral wool (rock wool) is highly efficient, rot-proof, moisture resistant, fire resistant, and unappealing to most pests. It’s an ideal insulation in many ways, but it’s more expensive than fiberglass and cellulose, and it’s hard for a DIY-er to install.

Rigid foam board is exceptionally efficient and so good at resisting moisture damage it’s often used in areas with a high risk of humidity issues and leaks. It doesn’t attract rodents, but carpenter ants like it. Installation is simple and largely mess-free, even for a DIY-er. The biggest disadvantage is its high cost, but you might find the extra efficiency and durability worth the investment.

Helping Your Insulation Last Longer

Spray Foam Insulation in Attic / photovs

Good maintenance is just as important as the type of insulation you choose. Problems such as moisture buildup, dust, and pest damage are common reasons insulation fails early, but they’re largely preventable. To catch problems early, inspect your accessible insulation at least once a year.


All types of insulation are at some risk of degradation from high moisture levels. Twice a year, check your roof and walls for leaks. Stay alert for signs of high humidity in your home, such as foggy windows and mildew problems, and takes steps to control the humidity before it damages your walls and insulation. If your attic is humid, consult a heating, cooling, and ventilation expert. This could be a sign the space needs more ventilation or insulation.

Physical Damage

The force of gravity can cause insulation to sag from ceilings and crawl space walls around 15 to 20 years after installation, but this can happen sooner if the insulation wasn’t correctly installed. Sagging insulation isn’t fully effective and leaves air gaps that encourage mold growth and drafts. If the insulation is still in good condition, you can staple it or use twine to hold it in place. If it’s compressed from moisture or damaged by pests, though, you’ll need to replace it.

Tears and punctures in batt or board insulation let air and heat through and reduce the insulation’s effectiveness. Damage that compresses the insulation also makes it less effective. This kind of damage can happen during home repair work, storms, and rodent infestations. It doesn’t make the insulation useless, but it does reduce its lifespan.

Dust and Dirt

If you spot a section of insulation that’s noticeably grimy, there’s a good chance that grime is coming from an air leak that’s been blowing in dust for months or years. Leaky ducts and gaps in exterior walls are common sources of leaks. Before you replace any dirty insulation, find and seal the leak to prevent a repeat of the problem.

Large sections of insulation that are visibly dirty are most likely also compressed and harboring mold and pest debris, especially if the insulation is more than 15 years old. Foil-backed insulation is even more affected because the dirt prevents the reflective foil from working. If your insulation is in this state, it’s time to replace it.


Mice, rats, squirrels, raccoons, and other rodents love to make their nests in insulation, and insects such as termites, cockroaches, and fleas do the same. In the process, they tear and trample the insulation and bring in moisture, dust, and other debris. Birds can cause damage, too, either by nesting in the insulation or by tearing off pieces to carry away.

This damage seriously reduces your insulation’s effectiveness and exposes you to bacteria and parasites, so once your insulation is infested, you’re better off replacing it. To protect your insulation, seal up gaps and cracks in exterior walls, minimize the clutter in your attic, and maintain trees and vines that contact your home’s walls.

Visible damage isn’t the only sign your insulation is failing. If you have trouble maintaining comfortable, stable temperatures or you notice your heating and cooling bills constantly rising, the problem could be worn out insulation.

With good home maintenance, you can expect your insulation to keep you comfortable for at least 25 years. Regularly inspect for signs of developing damage to keep your insulation in top form for its full lifespan.

Editorial Contributors
Henry Parker

Henry Parker

Henry Parker is a home improvement enthusiast who loves to share his passion and expertise with others. He writes on a variety of topics, such as painting, flooring, windows, and lawn care, to help homeowners make informed decisions and achieve their desired results. Henry strives to write high quality guides and reviews that are easy to understand and practical to follow. Whether you are looking for the best electric riding lawn mower, the easiest way to remove paint from flooring, or the signs of a bad tile job, Henry has you covered with his insightful and honest articles. Henry lives in Florida with his wife and two kids, and enjoys spending his free time on DIY projects around the house. You can find some of his work on Today’s Homeowner, where he is a regular contributor.

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