How Often Should Insulation Be Replaced?

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Insulation is one of the essential parts of a good home energy program because it will save you a ton of money on your heating and cooling bills. But, just like any part of your home, insulation is also prone to damages and may end up degrading over time.

So, how often should insulation be replaced?

Insulation can last for 80 to 100 years under the right conditions. However, insulation can start to degrade in as little as 15 years if moisture or rodents are present. If your insulation is damaged to the point that it no longer provides the insulating value once intended, you should replace the insulation.

Many factors determine whether or not you should replace your insulation and how often you should replace it. So, if you want to prevent air leaks, keep the energy bills down, and live in comfort and peace during the summers and winters, you should get to know more about your home’s insulation.

Lifespan of Various Types of Insulation Materials

There are many types of insulation available. Insulation is intended to last a long time. However, that is not always the case. The two leading causes of degrading insulation are water and animals. Insulation loses its effectiveness when it no longer provides resistance to airflow, which equates to higher energy costs. Let’s look at each type of insulation below.

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Spray Foam Insulation: How Long it Lasts

Spray foam insulation has become popular in newly-constructed modern homes because it is durable, air-tight, and reliable. Spray foam insulation can last a lifetime because it is mold resistant and does not absorb moisture. Once applied, spray foam insulation won’t move unless you cut it away.

Unless your spray foam insulation is disturbed by animals or other construction-related projects such as repairs or remodeling, you may never have to repair or replace it.

Fiberglass Insulation: How Long it Lasts

Fiberglass insulation is a popular choice in most homes because it is cost-effective and easy to work with. It comes as blown or batt insulation. Batt insulation comes in rolls and can be unfaced or faced insulation. Fiberglass insulation can last 80 to 100 years unless it becomes damaged by moisture or mold. Fiberglass insulation can begin to fail in as little as 15 to 20 years.

The number one problem facing fiberglass insulation is moisture. Fiberglass insulation needs to stay light and fluffy to maintain its insulating R-Value. However, it absorbs water, and once it’s wet, it can breed mold. If your fiberglass insulation becomes wet from a roof leak or a damp crawl space situation, it needs replacement regardless of age.

Also, as stated above, fiberglass insulation needs to be light and fluffy to be effective. Often, we will see compressed fiberglass insulation in attic spaces by storage or age. Once fiberglass insulation compresses, it loses effectiveness and needs replacement.

Blown-in loose-fill insulation is more energy-efficient than batt insulation because it can fill all air gaps and, if undisturbed, prevent heat loss better. However, blown-in insulation can’t be used in crawl spaces.

Proper insulation needs to maintain a certain thickness to prevent interior heat transfer. Measure the thickness of your attic insulation and compare it to the chart below. Replace your fiberglass insulation if needed.

R-ValueFiberglass Batt
Fiberglass Blown-in
R-3010″ to 12″12″ to 14″
R-3812″ to 14″14″ to 16″
R-4916″ to 18″18″ to 20″
R-6020″ to 22″22″ to 24″

Insiders Tip: If your attic insulation is damage-free, you can add new insulation directly over existing insulation, provided no gaps exist. Blown-in insulation fills any voids and gaps that may exist when adding insulation.

Cellulose Insulation: How Long it Lasts

Cellulose insulation is eco-friendly because it’s made from recycled materials. It is also more effective at blocking air movement than fiberglass insulation.

Cellulose insulation only has a lifespan of 20 to 30 years and will start to degrade naturally about 15 years after installation.

Cellulose is loose-fill insulation used in attics. It’s well suited as secondary insulation blown in over fiberglass batt or other longer life insulations. So, while it is more environmentally safe, it only has about one-quarter of the life expectancy.

Like other common types of insulation, cellulose is prone to moisture damage and mold growth. Once cellulose insulation is wet, it needs replacement regardless of age.

Mineral Wool Insulation: How Long it Lasts

Mineral wool is durable insulation available in rolls, batts, or blown-in varieties. Mineral wool insulation can last 30 to 80 years, depending on the specific base material used, such as rock wool, glass wool, or slag wool.

Like other forms of insulation, mineral wool insulation is prone to moisture damage and mold growth. Once the insulation is wet, it needs replacement regardless of age.

Mineral wool insulation is well suited to secondary insulation blown in over fiberglass batt or other longer life insulations.

Should Old Insulation Be Removed Before New Insulation is Installed?

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If your insulation has degraded too much and needs to get replaced, you would naturally want to install new insulation. Does that mean that you have to remove the old insulation? Can you add the new insulation over the old insulation to reduce the new insulation’s installation costs?

Yes, you can install new insulation over existing insulation in attics, provided the insulation doesn’t have water damage or mold present. Experts suggest that it is acceptable to add new insulation over the existing insulation. Installing new insulation over existing old insulation applies to attic insulation. You should replace the wall and crawl space insulation.

When you add new insulation over the existing insulation, you must ensure that the old insulation isn’t wet or moldy. Mold insulation will look black in spots or streaks. In short, the old insulation has to be as dry as possible.

How Long Does Crawl Space Insulation Last?

We often think about our walls and attics when it comes to insulation most of the time. Not many people realize that insulating your home’s crawl space is also just as crucial if you want to improve its energy efficiency.

While most insulation can last 80 to 100 years, insulation installed inside crawl spaces can only last about 10 to 40 years, roughly half the lifespan of other areas of your home. The main culprit affecting insulation in crawl spaces is moisture and mold caused by groundwater and ductwork.

If your home has a crawl space, chances are it’s already insulated. However, this is not always the case. Some homes located in southern states have no crawl space insulation. In recent years, contractors have started removing insulation from crawl spaces and opting for encapsulation systems.

But if you have already insulated your crawl space, you also have to consider that the insulation in your crawl space won’t last long because animals and moisture can easily damage it.

How Moisture Affects Crawl Space Insulation

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Insulation in crawl spaces becomes wet by damp ground and condensation from the ductwork.

If you live in an area with high groundwater levels, your crawl space should have a moisture barrier – a thick layer of plastic covering the ground in the crawl space. Moisture barriers (vapor barriers) keep wood moisture levels under control, prevent dry rot, and deters wood-destroying organisms.

However, sometimes a vapor barrier, while necessary, may not be enough to control moisture. Ventilation is also essential. Crawl spaces require a good source of airflow to keep moisture levels low and the crawl space dry.

However, sometimes a vapor barrier and ventilation are not enough to control moisture. So now what?

The reason vapor barriers and ventilation may not be enough is something is obstructing airflow – likely your home’s HVAC ductwork.

The ductwork’s large supply air trunks often block airflow in crawl spaces. I’ve seen some crawl spaces with literally no clearance around ductwork. So what does all this have to do with insulation?

If the conditions inside your crawl space are dry, moisture and mold will form on your insulation. Wet insulation becomes stringy as the fibers start to separate. You need to replace damp insulation no matter how old it is.

Replacing the insulation does little good if you don’t address the source of the moisture problem. You may need to replace ductwork or relocate air ducts from your crawl space to your attic, which airflow and removes the source of condensation from the crawl space.

If relocating your HVAC ductwork to the attic is not possible, you will likely need a crawl space encapsulation with a commercial-grade dehumidifier to control crawl space conditions and keep the insulation dry.

When Should Crawl Space Insulation be Replaced?

How often should you replace crawl space insulation? Well, similarly, insulation in crawl spaces should last upward of 40 years when the conditions are right. However, crawl space insulation may need to be replaced in damp conditions as soon as 10 years after installation.

In other words, you should replace your crawl space insulation as often as needed, primarily when the signs are pointing to the fact that it needs to be changed. The best way to know this is by having an expert inspect your crawl space insulation.

You can still expect most crawl space insulation to last 20 to 40 years as long as conditions are right.

How Long Does Attic Insulation Last?

Similarly, attic insulation should last for the recommended 80 to 100 years in ideal conditions. However, attic insulation exposed to animals and moisture will affect longevity. Attic insulation under normal conditions can last 40 to 80 years.

How Often Should Attic Insulation be Replaced?

How often should attic insulation be replaced? Attic insulation should last upward of 80 years when the conditions are right. Attic insulation may become damaged and need replacement as soon as 15 years after installation. At 15 years, attic insulation can degrade due to heat, moisture, humans, or animals.

If you experience roof leaks or storm damage resulting in moisture damage, wet insulation will need replacement. Wet insulation can occur from improperly vented bathroom fans, HVAC condensation leaks, or ventilation problems causing a lack of airflow.

Other problems, like rodent infestations, can damage insulation too. Often, squirrels and other rodents seek shelter in attics for warmth by bedding in the insulation, which leads to damage to the insulation material caused by feces, urine, and potential diseases. In other words, have it replaced as needed after inspecting your insulation for damages.

People can also damage insulation. Compressed attic insulation occurs when people store personal items inside attics. Compression occurs when fluffy insulation is pressed tightly together under an object’s weight, such as boxes or storage bins. People will sometimes lay wood down over the insulation to create a walking surface where no walking surface is present. As insulation becomes compressed, the R-value diminishes.

In other words, undisturbed attic insulation can last for 80 years or more. Unless disturbed, you should not need to replace the attic insulation sooner.

How Long Does Insulation in Basements Last?

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The insulation lifespan in basements will often be determined by whether the basement is finished or unfinished. Basement insulation is usually in the same boat as your crawl space, but you have to consider that your basement isn’t as exposed to the elements as your crawl space.

The most significant difference between an unfinished basement and a crawl space is that it likely has a concrete basement floor. That means that you have fewer worries when it comes to your basement, but that doesn’t mean that its insulation would last indefinitely.

The fact is that basement insulations are still subject to certain negative external factors you have to worry about, like rodent infestations and moisture that could quickly degrade the insulation material.

That said, basement insulations would generally last for 30 to 50 years. But because it is less likely to suffer from severe damages, you probably won’t need to replace your basement insulation for another 20 or so years as long as you keep your unfinished basement dry and as watertight as possible.

How Long Does Exterior Wall Insulation Last?

Unlike the other insulations in your home, wall insulation tends to last longer because it is concealed and protected from moisture and other factors that can damage and degrade it. Theoretically, the insulation hidden in your walls’ cavities should last for as long as your entire house will. 

Wall insulation theoretically will last longer than most other insulations because it has less exposure to weather and animals. But that is in theory alone because some wall insulations may not have been installed very well and may end up degrading faster than expected.

Still, wall insulation is less likely to suffer damages from moisture or dampness and is safe from rodents and other types of animals that can degrade their quality. That means that wall insulations can last for up to 80 years or more without the need to be replaced.

Unless you live in a 100-year-old house, chances are you’ll not need to replace your exterior wall insulation any time soon. Old houses generally have low insulation levels and are not air-tight by design. Old houses allow the free flow of air but are very energy inefficient due to their natural draftiness.

Unfortunately, the only way to improve exterior wall insulation would be to remove the outer wall siding or interior wall plaster. Therefore, many people tolerate the draftiness and focus on attic insulation instead.

Keep in mind that opening the exterior walls or plaster will require removing potential lead-based paint or asbestos-contaminated materials. You’ll also need to update old wiring or plumbing, making for a costly home renovation, explaining why most older houses have likely never replaced exterior wall insulation.


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.