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Stack Effect? Say What?

We’ve said it a hundred times; you can’t have a mold problem without first having a moisture problem. Mold needs moisture to grow and that’s all there is to it. You can’t have mold without water. So if your house has no water leaks, you shouldn’t worry about mold, right? Nope. It’s easy to focus on leaky plumbing or flooded basements as sources of moisture, but don’t forget about the air circulating throughout your home. It carries moisture in the form of water vapor and humidity throughout the HVAC systems, exhaust fans, and living spaces in your home. That moisture can lead to mold growth due to something called the stack effect.



Never heard of stack effect? Long story short, it is the pattern of air flow throughout a building based on temperature and structure. During colder months, cold air is pulled in close to the ground through basements, crawlspaces and air leaks along the main level. That air replaces warm indoor air as it rises to the upper levels and attic of the home.  In warmer months, just the opposite occurs. Warm air is pulled in through the attic, upper level air leaks and other sources. As that air cools, it flows to lower levels and new, warmer air is pulled in to replace it. All that sounds fine right? For the most part, it’s not a terrible thing. It can lead to some energy loss depending on severity of air leaks and may explain some temperature differences between living spaces. It’s the moisture part of the equation that causes the problems.

As air enters and leaves your home, the temperature differences between the inside and outside air can cause condensation and high humidity. That’s typically all the moisture you need to feed a mold problem and why mold frequently grows in attics, crawlspaces and basements. They are the entrance and exits points for air due to stack effect. They are also the places we tend to spend the least amount of time; so mold can grow unchecked and out of control. It’s important to periodically check all areas of your home for signs of moisture or mold concerns.  If you spot something that causes concern or want us to do the checking for you, we are happy to help.