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What is the Stack Effect?: A Problem for Household Mold

Your crawl space is a damp, dank place. If it’s not encapsulated, moisture is getting in there, and that’s causing mold to grow.

Now, you might think, That’s no big deal! If mold is going to stay down there, at least it’s away from where I normally live and move and breathe.

Well, think again. 50% of the air you breathe in your home comes from your crawl space. So, if there’s mold down there, there’s mold spores everywhere.

The culprit here is a process called the “stack effect.” In this article, we’ll tell you all you need to know and what you can do to stop it.

If you take one thing away from this article, it’s that when you see (or breathe) mold, it’s probably coming from your crawl space. The best thing you can do right now is to call Dry Pro, the leading crawl space repair expert serving areas in and around Charlotte, Rock Hill, and Concord. Schedule your free crawl space inspection today!

What is the Stack Effect?

the stack effect illustration

The “stack effect” refers to the process in which hot air rises up through each level of your home, leaves through your attic and upper levels, and creates negative pressure which vacuums air into your crawl space or basement.

The name comes from the phenomenon of air rising in temperature as it rises through your home—”stacking up” towards the top.

What The Stack Effect Means for Your Home

condensation on crawl space pipes

1. Moisture and Condensation

Depending on the season, the air inside your crawl space or basement is either cooler or warmer than the air outside. If it’s cooler (ie. in the summer), the air will bring in moisture that will form condensation on pipes and other features like your floor joists.

Humidity is often measure an a 100% scale, 100% being the point at which the water content outweighs the oxygen content. For every degree of difference between the higher temperature outside and the cooler temperature in your crawl space, the humidity level will go up by 2.2%. So, if it’s 85 degrees outside and the humidity level is 80%, and it’s 73 degrees in your crawl space, then the humidity level will rise to 106.4%, surpassing the point at which it comes to rest and gather on cool surface.

mold in crawl space on wooden beams

2. Mold Growth

Mold’s favorite food is moisture and natural fibers. As the relative humidity in your basement or crawl space rises to 60% or higher, mold will start to grow in your crawl space.

As mold reproduces, it releases millions of allergenic mold spores into the air. In fact, research shows that a single square inch of drywall can contain as much as ten million spores!

Mold and rot will also wreak havoc on your home. Damaged wood, structural issues, and ruined personal property are all consequences of mold, mildew, rot & humidity in a basement or crawl space.

The Stack Effect

3. The Stack Effect Circulates Mold Throughout Your House

Because of the stack effect, these mold spores will not be confined to your basement or crawl space. As air moves up from these spaces into your home, it will bring mold spores and humidity along with it. If you notice that you suffer from symptoms such as a runny nose, watery eyes, mild allergic reactions, a scratchy throat, fatigue, or headaches at home that seem to disappear once you leave the building, mold allergens may be the culprit.

Controlling Humidity & Mold in North Carolina

The key to controlling mold in your basement or crawl space is to eliminate the humidity that keeps it thriving.

At Dry Pro Foundation and Crawlspace Specialists we recommend starting by sealing off any vents, covering any exposed dirt and concrete, and installing airtight crawl space doors. Replacing drafty basement windows will also help hold back outside air.

Once this has been completed, it’s a great idea to install either an energy-efficient basement dehumidifier or crawl space dehumidifier. This will remove any existing humidity in the space and keep it dry in the future.

We offer free basement & crawl space humidity control estimates in North Carolina, including Charlotte, Gastonia, Concord, and many areas nearby. Contact us today to get started!

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Stack Effect FAQs

Mold is a microorganism that is capable of triggering allergies, illness, or in the worst-case scenario, hazardous breathing problems. Long-term exposure to mold damages your respiratory system, so a moldy crawl space is a health hazard. Even if you don’t spend much time don’t in your home’s crawl space, mold can still cause health problems because of the stack effect which moves mold spores into your home as warm air rises.  

While DIY methods are tempting, they often fail to fully eliminate mold or address its causes. We advise against entering potentially hazardous crawl spaces alone. Rely on Dry Pro for professional mold treatment and moisture management in your crawl space. Contact us for a free inspection

While both can affect your home’s structure, wood rot primarily targets crawl space joists and beams, leading to floor sagging. Unlike wood rot, certain molds can exacerbate health issues like asthma and allergies. Dry Pro identifies and addresses whichever problem your crawl space faces during our free inspection.

Michael Wilcher

Michael Wilcher

Michael Wilcher is the Content Lead at Groundworks, helping us to answer all of our customers biggest questions about foundation repair, basement waterproofing, crawl space encapsulation, and concrete lifting. In his free time, Michael enjoys collecting vinyl records, watching Formula 1 Racing, and reading philosophy. He holds an MPhil from the University of Cambridge.

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