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9 Surprising Reasons Why Insulation Gets Wet

Nobody wants wet insulation, even if you can dry it out. Handling compromised R-value, mold, and the cost of replacing aren’t my favorite activities either. While we know the common culprits, like a leaking roof or pipe, there are other possibilities to consider when you aren’t finding the typical leaks.

Surprising reasons why insulation gets wet:
  • Pipes and ducts are not insulated
  • The walls are damp
  • Attic/soffit vents are blocked
  • Ducts are cracked
  • Animals are living in the walls/roof
  • The insulation is insufficient
  • There is too much insulation
  • The insulation has moved
  • The house is drafty

1. Pipes and Ducts Aren’t Insulated

If your pipes and ducts are not insulated, then you will have some condensation problems. This is because insulation keeps the temperature of the air in the pipes and ducts separate from the temperature of the air outside them.

Water will condense on the pipes and ducts if the air temperature within them is lower than the air around them.

Technician checking the hvac duct.jpg

Heat will transfer down the temperature gradient from the warmer air outside the duct to the cooler air inside the duct. As air cools, it can carry less moisture causing condensation on the outer surface of the duct.

Considering your pipes and ducts typically run through spaces that contain insulation, this condensation can build up and cause moisture issues with the insulating material.

Condensation can also be a problem for exhaust system ducting. These systems contain warm air that needs to be insulated. If water condenses in the duct run, this can cause damage to the shell or compromise seals (mold), allowing water to seep out of cracks. Your insulation will also end up wet.

In terms of ducts, you will likely notice dripping. This will be more noticeable in colder weather since the temperature difference is greater.

Duct Insulation R Value Guide (Thickness to R Value Table)

2. The Walls Are Damp

Not all walling materials are fully waterproof, and insulation will not solve this. Most materials, even tiles, typically need a treatment of some kind to prevent water from absorbing into and passing through the walls.

If there is a missing vapor barrier on the wall into the living areas, you can end up with condensation forming in the wall cavities. This can soak into the insulation and will also cause mold problems on the walls from humidity.

This is particularly important for bathrooms, which are exposed to a lot of humidity. Even the ceilings in bathrooms require waterproofing.

So, you should protect the walls by painting on liquid membranes (i.e., Drylok) or using sheeting membranes (these will take time to dry), or you can use thermoplastic waterproofing. You should also make use of bathroom paint and drywall that is rated for bathrooms.

Drylok, sheeting membrane, thermoplastic waterproofing and bathroom paint.jpg

3. Attic/Soffit Vents Are Blocked

Something to know about attics is that they need to be ventilated as part of the air system for your home. This is achieved through vents that are installed in the roof.

There are typically upper vents (i.e., ridge vents or the like) and lower vents (i.e., soffit vents) that provide passive ventilation to the roof space.

These vents work in tandem to allow air to flow in and out of the attic space. This airflow assists with temperature regulation and permits moisture in the space to be vented out.

If these vents get blocked, then the moisture is trapped in the attic. Since insulation is installed in attics, this can create issues with the material getting wet.

These blocked vents will also interfere with the passive ventilation of your home, which means you might notice that warm or cool air is not distributed through your home properly. Or you might notice your attic is getting hotter than usual.

4. Ducts Are Cracked

Ducts for exhaust systems are associated with moisture. The air the exhaust ducts remove from dryers, kitchens, and bathrooms contains steam. The air within these ducts needs to be kept separate from the environment outside of the duct, which is why they must be insulated.

Ducts can end up cracking when there is physical or water damage to the run. Cracks compromise airflow through the ducts because the pressure balance is thrown off. This slows the air, keeping it in the ducts longer and allowing it to cool before being exhausted.

This, along with exposing the humid air to the cooler temperature outside the duct, results in condensation.

This condensation can then drip out of the crack, soaking into the insulation for the duct and any insulation nearby.

This problem can be indicated by water dripping out of bathroom fans or gathering around a dryer since it isn’t exhausted fast enough and is running back through the ducts.


Your exhaust system can also struggle with the pressure imbalance, so you may notice that it takes longer for your kitchen and bathroom air to clear or that your dryer is getting hotter than usual.

5. Animals Are Living in Your Walls/Roof

If you have animals in your walls or roof, your insulation can get wet as they come in wet to take shelter from the rain in your nice and dry house. They can also wet the insulation by urinating on it.

You might be thinking that surely any gap in your house large enough to let an animal in is also large enough to let rain in to wet the material. This would certainly be a more likely cause, except that these gaps aren’t always near your insulation.

Animals can get in at one spot and move to your insulation, making it wet. They can also get in at an opening that isn’t letting rain in, like the gap under the soffit.

6. Your Insulation Is Insufficient

Sometimes the insulation present is not enough. Insulation can degrade over time, meaning you are losing R-value. Damage from things like dust and water can also compromise the R-value of the insulating material.

It can also be a result of using unsuitable insulation materials, such as moving blankets or packing peanuts.

When there is insufficient insulation, you will have problems with condensation that can cause a moisture problem with your insulation. This is because warm air holds more moisture than cold air; without enough insulation, the indoor air can be influenced by outdoor temperatures.

When inside air is cooled too quickly (particularly in humid areas), it causes water droplets to form as the air cannot hold all the water it was previously carrying. Therefore, we get condensation, which is problematic.

You might notice issues with dampness, temperature regulation, mold, and soundproofing if your insulation isn’t providing the necessary R-value.


Depending on the state of the insulation, you might be able to add more to reach the intended R-value for the area, but you might need to replace all the insulation.

7. Too Much Insulation

On the other end of the scale, there is such a thing as too much insulation.

Now, there is no official upper limit to the amount of insulation you can have. However, when you have too much, it can block up the vents.

When airflow is compromised, it can readily lead to a buildup of moisture in the attic, which can wet the insulation.

8. The Insulation Has Moved

As insulation ages, it can also move. Unless it is spray foam or foam board, the fibers of your insulation can compress with age and sag into the bottom of the spaces and cavities.

Or, it might be that the cavity wasn’t enclosed properly, giving the insulation space to change positions. This means that even if you have enough insulating materials installed, you might not benefit from proper insulation.

As mentioned above, without the correct R-value, the air within your home is more easily influenced by unconditioned external temperatures. So, if your insulation is not covering the area it needs to, you can end up with condensation troubles.

Since insulation is there to help keep conditioned and unconditioned air separate, if the insulation is not in a position to do its job, we are, again, looking at condensation issues.

9. Your House Is Drafty

If there are too many air gaps in your home’s thermal envelope, then you can have a problem with balancing the air pressure system between your home and the outdoors. Unconditioned air can be transferred inside through these, creating drafts.

This can come from a lack of vapor barriers, the presence of spaces around door and window frames, and even unsealed baseboards.

Man wearing gloves caulking the gap in the window.jpg

You will notice cold spots in your home where conditioned air is leaking out and being replaced with air from outside. You will likely be paying extra on utilities as your HVAC system must work harder to heat or cool your home.

Because the air coming in is a different temperature (unconditioned), this will create condensation, which can gather in wall and floor cavities and in attics where insulation is present.


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