Mold Under Vapor Barrier In Crawl Space: Reasons And Preventive Tips

Having a damp crawl space smell should be a surefire indication of possible mold under vapor barrier in the crawl space.

Almost nobody inspects the basement corners or spends time in the crawl space. So, the growth of mold is somewhat inevitable.

So, let’s talk about why there is black or white mold under vapor barrier and I will explain exactly how you can prevent this problem.

Why Is There Mold/Condensation Under Vapor Barrier?

white mold under vapor barrier

Moisture in the crawl space is a common problem for every house with crawl space vents. That moisture eventually leads to other problems like mold and mildew growth.

Not just the crawl space vents, several other factors are responsible for such problems. You need to figure out the reasons first before you can take any preventive measures.

Let’s talk about those factors that are responsible for the white and black mold under vapor barrier one by one:

  • Through Crawl Space Vents

Homebuilders used to add crawl space vents to the foundation to prevent moisture problems. But recent studies have shown that such vents actually do more harm than any good.

Not just by letting water in, such vents will let hot and damp outside air in the crawl space and lead to mold and mildew problems.

So, if your house has crawl space vents, seal them up to prevent the outside damp and hot air to get inside the crawl space.

Also, cover the crawl space floor and walls with a vapor barrier to prevent moisture and water from coming through the foundation’s walls.

Now, if you have a vented crawl space, there can be still moisture issues. So, the following reasons can be responsible.

  • Through Plumbing Leaks
damp crawl space

There can be leaks and cracks in the water supply pipe or drain pipe. Water from those leaky pipes can form puddles on the crawl space floor.

This will ultimately lead to mold growth and invite other pests.

So, you should inspect whether you see any dripping water inside the crawl space while you’re running the water inside your home.

You should call a plumber to fix such leaks and ask him to inspect for standing water under the shower, toilet, or below the tub.

  • Leakage of Groundwater

The soil around the foundation of your home contains water and such water can seep into the crawl space in several ways like the cracks of the concrete wall, or through the block walls, or under the footing, etc.

A good way to stop this water from entering the crawl space is by installing a sump pump and a perimeter drainage channel in the crawl space.

  • From Exposed Dirt

Another way of having moisture and eventually mold under the crawl space is from the exposed dirt in the crawl space. Yes, any exposed dirt in there will add moisture to your crawl space.

Let me explain how…

As the ground is usually damp, the water from the dirt is evaporate towards the crawl space as the damp soil dries. You need to do something about this.

A great way to deal with this is by adding a vapor barrier over the dirt floor. But don’t confuse vapor barrier with crawl space encapsulation!

Having a vapor barrier over the dirt floor will prevent the water vapor to evaporate upward into the crawl space.

Apart from this, you can also think about fixing the grading around your house and doing some cleaning for the downspouts and gutters.

So, these are the 4 prominent causes of why you have mold behind vapor barrier. Usually, you will have a combination of the above four (4) reasons.

Now, let’s talk about what to do to avoid this problem.

Fixing And Preventing Mold/Condensation Under Vapor Barrier

condensation under vapor barrier

For a serious mold outbreak, you must hire a professional to safely remove the mold.

Don’t try it yourself because if you are not careful the mold spores may be sent into the air and intoxicate your entire home.

But the good news is you can take preventive measures yourself so that you don’t end up having a mold outbreak in the first place! Here are preventive measures you can take:

  • Get A Dehumidifier

Keeping the crawl space dry is vital to avoid mold growth. When the humidity level reaches 60%, the growth of mold begins!

And when you use a dehumidifier, you can keep the humidity level in check and avoid mold behind the vapor barrier.

  • Fix Any Leaks

There could be leaks around the plumbing components and fixtures, HVAC ducts, pipes, etc. Leaks around that stuff can be another reason to have water or mold in your crawl space.

So, I would occasionally inspect those and fix those leaks if I were you.

  • Check Your Dryer Vents

Check whether the dryer vents are taking the moist air outside or not. You should not let the dryer vents take the hot and moist air into the crawl space.

  • Insulate Against Sub-floor of Crawl Space

You can use plastic sheets to cover the floor to create this sort of insulation against the sub-floor of your crawl space. Such insulation will prevent moisture from coming from the ground.

Not just moisture, using plastic sheets will prevent water from seeping into the crawl space too.

  • Functioning Gutters And Downspouts

Your gutters and downspouts should keep the water away from your house and should not let the water accumulate anywhere near the foundation. They should not let the water seep into the crawl space.

Now, are they doing their job? You should occasionally inspect your gutters and downspouts in this regard.

  • Check The Crawl Space Ceiling And Foundation

There will be water under the vapor barrier in the crawl space if there are holes in the ceiling of the crawl space. Seals those holes up so that the water can’t make its way down.

You should check the below-ground walls for cracks as well and fix them if there are any.

  • Regular Inspection

This is the best thing you can do if you inspect your crawl space at least twice a year. That way it won’t come to the mold spread situation where you will have to call a professional to get rid of it.

There you have it! I can promise you if you just follow the preventive measures I mentioned above, you should be able to avoid this unpleasant situation.

Frequently Asked Questions (FAQs)

Does mold grow under crawl space vapor barrier?

Yes, the crawl space vents and moisture from the ground can lead to mold growth under the crawl space vapor barrier. Not just mold, it can lead to mildew and dry rot growth too. Insects love to thrive in there.

Can a vapor barrier cause mold?

The vapor barrier is not responsible for the mold. In fact, it helps to prevent mold growth in your crawl space. However, when the walls get wet due to many reasons, the vapor barrier alone won’t help prevent mold growth.

Is it normal to have moisture under vapor barrier in crawl space?

No. It happens but it’s not normal. Such moisture under the vapor barrier will lead to mold and mildew growth. Usually, it happens when you did not install the vapor barrier the right way.

How do I get rid of mold in my crawl space under my house?

I would recommend hiring a professional to get rid of it considering the hazardous effect the mold spores can have on you if you try to do it yourself. Once the molds are removed, you can take preventive measures to avoid this situation in the future.

How do you seal a moisture barrier in a crawl space?

Using plastic sheeting and foil-faced rigid to perfectly seal a moisture barrier in a crawl space.

Final Thoughts

Usually, the combination of more than one issue leads to water or mold under vapor barrier in crawl space. I believe you can spot the reasons now.

If you want to avoid paying the professional a hefty price, taking preventive measures will be your best damp crawl space solution.

It’s not a good place to visit but for the sake of preventing hazardous mold, inspect your crawl space every now and then to avoid having a mold outbreak.

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