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The Stack Effect

Open dirt crawl spaces are bad for homes because they let outside air, water, and pests inside.

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Mold, rot, and the resulting damage are something most homeowners will worry about at some point during homeownership. The damage to your house’s structure and your air quality can lead to repairs costing thousands of dollars. Sometimes, it’s even money out of pocket as opposed to an insurance claim. Because mold and rot reduce your property value, you may wonder what the culprit is, but most importantly, how to stop it. 

The stack effect may be responsible for the mold in your home, either partly or fully. Sometimes referred to as the chimney effect, this describes air movement within a home or building. The unique movement of air is a result of air buoyancy, which occurs from the difference in temperatures from the outside to the inside of the home. The stack effect is a natural process that helps with ventilation and air infiltration, but it also promotes humidity and the growth of mold. 

Let’s explore how the stack effect can have a damaging effect on your home and what you can potentially do to minimize the risk.

Problem Signs Concerning the Stack Effect 

Though it’s difficult to think about anything going wrong with your home, there are signs as issues begin to form. Even the stack effect will leave signs that should keep all homeowners vigilant. The quicker you catch a problem brewing, the easier and cheaper it will be to fix. 

  • Cold Areas  

Part of the stack effect is that air comes in from the lower sections of the home, such as the basement or crawl space, and escapes up through the top of the house, either the roof or the attic. As the air comes in, it heats up before it escapes as it passes through the rest of the home. You won’t feel any temperature difference throughout the house until you reach the floors where it comes through. 

Instead, you’ll feel the temperature variance around the areas where the cold air gets pulled into the house. There will be cold drafts next to your home’s exterior walls and cold floors above the crawl space. When the stack effect is in full swing, the temperature change between the lower floors and those up higher will be noticeable. 

  • Continuous Heating or Cooling  

The stack effect pulls in cold air, which heats as it rises before it ultimately escapes. Since homes are always exposed to cold air from below, the heating system has to work overtime. Your HVAC system will end up strained as it struggles to heat your home to your comfort level. You may find your HVAC giving up earlier than it should, needing to get replaced more frequently. Of course, the same thing would happen in the summer, with hot air coming through and cold air escaping through the house’s higher floors. 

A part of the by-product of your HVAC working overtime to either cool or heat the air in your home is the higher bill you’ll see every month. Your bill may rise slowly or there could be a drastic jump, but it should catch your eye the closer you look. Nowadays, smart thermostats are also there to let you know when your HVAC system is working harder than it should, giving you a heads up that a checkup is needed. 

  • Noises in the Home 

As air passes through the house on its way through the bottom and out through the top, the house will make noise. Small cracks where air passes through into the home will create noise, almost like a whistling. You may not hear the noise throughout the entire home, but you’ll hear it the closer you get. 

Other parts of your home will start getting affected by the air getting pulled into the house. When it’s cold outside and hot inside, you’ll find doors are harder to open or close, which could cause a scraping or creaking against the door frame or floor. The opposite is true when the air pulled in is hot instead of cold. This time, the door will actually slam, sometimes all on its own, and sometimes with your help.  

  • Built-up Moisture 

One of the more significant problems with the stack effect is built-up moisture throughout the house or, most notably, in the basement or crawl space.  The humidity inside a home, or even outside, measures the amount of water currently in the air. The higher the humidity level, the closer the air gets to being “full” of moisture. As a rule of thumb, the higher the temperature, the more moisture it can hold. 

The stack effect causes all the warmer air to move upward through your home and the cooler air to remain below. Humidity inside your home will travel throughout the house but will prove problematic in the house’s lower levels. Since those areas, like the basement or crawl space, remain naturally cooler, they hold less water. 

Once the air reaches capacity and can hold no more humidity, it will start turning into water droplets that deposit on cool surfaces such as wood, metal, or concrete. The excess water sitting on surfaces inside the basement or crawl space will cultivate mold and help it spread throughout the house. Depending on how long the stack effect has happened inside the home, you might start to see mold form around your basement or crawl space area.

Causes of the Stack Effect

Let’s review how the stack effect works and why it happens in more depth. 

How Does It Work? 

The stack effect happens in larger buildings but also in two-story homes, especially those with a crawl space or basement. The entire home will essentially act like a chimney where the air at the bottom (the hottest air) is pushed upward before being forced out to leave the house. Typically, the stack effect will only happen when the air outside is much colder than the air inside. 

The entire air movement between the cold and hot portions of the house only creates a large draft throughout every room. Though it might not sound like a huge problem to have some air come into the house, it will not stop all on its own, raising your electricity bill and potentially making you buy new appliances. 

What Causes the Stack Effect? 

You’ve learned the stack effect is air pulled in from the outside to the inside of your home, which then escapes through the attic or roof. Cracks inside the home, especially in the basement or crawl space, will allow air to slowly seep into your house, starting the stack effect cycle. 

The escaping air perpetuates this cycle either through cracks at the top or even household members opening windows. Since the home is hotter at the top before the air escapes, it’s not uncommon for homeowners to try and vent the air to help it cool down.

Solving the Stack Effect Problem

Once you’re aware of what causes the stack effect and how it can have a negative impact on your home and well-being, you should take a look at ways to solve the problem. Innovative Basement Authority in Minnesota, North Dakota, and eastern Montana has ways to help you secure your home against the potential pitfalls of the stack effect. Let’s take a look at some ways this process is solved.

  • Air Sealing  

Cracks within the home will only help start the problem and facilitate its continuance. Any type of crack allows air, hot or cold, to move into the home and begin the stack effect process. During the winter, cold air will come through the bottom, and warm air will escape out the house’s top. When it’s summer, hot air will come in at the top of the house and escape through the bottom, allowing mold to grow inside the home. 

Take a look through your attic for any cracks around lights, the chimney, vents, wiring, and exhaust fans, since that is where they are likely to form. Seal areas where the attic meets the wall as an added precaution to stop the flow of air into the home and out as well. 

When looking through your basement or crawl space, be sure to check around the rim joists, the sill plate, and any penetrations into the floors for things like ductwork, wiring, and plumbing. These are high problem areas and should get reinforced with a sealant. 

  • Insulation 

Upgrading your insulation is a great way to fix the stack effect in your home. Poor insulation in the basement or crawl space will help air come into the home in the winter. Air is then likely to escape through the attic or top portion of the home if the insulation hasn’t been upgraded there as well. 

The focus of your insulation upgrade should be the exterior walls of your home, as well as windows and doors. You want to try and keep the warm air in when it’s winter, but at the same time, avoid letting cold air infiltrate from the bottom of your home. 

  • Humidity Control 

Even if you’re unable to completely stop the stack effect in your home, you can attempt to control the humidity level to prevent mold from growing and becoming a larger problem. Apart from sealing off areas as mentioned above, you can install airtight doors around the basement, exterior crawl space vent covers, better windows, and even a dehumidifier. A basement or crawl space dehumidifier will remove excess humidity that would normally turn to water droplets, instead keeping it dry and away from any types of mold. Controlling the humidity in your home will help stop the spread of mold and spores from infiltrating not just the basement or crawl space, but also the rest of the organic material inside your home. This will save you property damage and help you preserve the health of yourself and your family.

The Stack Effect


The stack effect has a few different driving forces behind it that start or perpetuate the problem. Learning a little more about these will help you understand how to solve the problem within your home.  

  • Height of the Home 

The taller the home (or the building, if it’s commercial), the stronger the convection. The stack effect has a bigger effect on the entire home, so the more floors there are, the more damage that can be done. Likewise, it’s far easier to overlook the subtle signs of mold damage if you happen to have a two or three-story home. 

Because of this, it’s important for larger homes in damp areas to look into preventative solutions. For example, you may need a dehumidifier set up in the basement, crawl space, or other spots of your home. This could be paired with repairs on any of the structural support beams, should mold have already begun to settle into the walls or floors of your multi-story home. 

  • Interior-Exterior Temperature Difference  

The larger the difference in temperatures, the more likely they are to mix together. If the weather is significantly colder in the winter, it will almost certainly come in through any crack or lack of insulation. This will only perpetuate the humidity problem in the basement or crawl space. 

That might be paired with other damages caused by sudden heat waves or freezes. For example, this can also lead to soil shifting or bowing walls, which can create access points throughout your home to let in pests. Having a professional examine your home for signs of mold is one step, but having them also look for related issues while they’re there can help you save on repair costs in the future. 

  • Air Leakage 

This is the driver you can directly prevent, unlike the first two. Air sealing is one of the best ways to limit air seeping into the home, causing the stack effect to build inside the house. A professional can seal the most important parts of the home in the basement, crawl space, and attic. 

A professional will be able to properly assess where the seals are needed and what types are necessary. For example, your basement may benefit from simple repairs to cracks or gaps in your walls. It may also need more advanced fixes, such as a vapor barrier. Scheduling a free inspection is the quickest way to get a customized solution for your exact home, which saves you money long term.

The stack effect can significantly impact the structure of the home and the health of the family living inside. Some problems may not seem as obvious as others, but here is an overview of what you can expect. 

  • Mold  

The stack effect facilitates the growth of mold around the basement or crawl space of the home. As explained above in more detail, due to the cold air at the bottom of the home in the winter, the air will get oversaturated with water, causing it to turn into water droplets and settle along any cold surface like wood or concrete. 

Mold spreads rather quickly as it eats away at any organic matter it comes across. In some instances, it can travel through non-organic matter to get to its food source. This means that once a mold problem starts, it becomes nearly impossible to solve it without spending thousands of dollars. The best thing to do is to try and prevent it from starting in the first place. 

  • Overwhelmed HVAC 

Whether it’s the winter or summer months, the HVAC system in your home will have to work double-time in order to keep up with your desired temperature. For example, in the winter, cold air will start infiltrating the home from the basement or crawl space, along with surrounding areas. This air will rise toward the top of the house, where the HVAC system will work overtime to heat it to the temperature you’ve set. Of course, this air then escapes, and the cycle starts over again. 

You’ll find your HVAC overwhelmed and start to endure wear and tear quicker than it should. This points to potentially thousands of dollars’ worth of repairs more often than they should take place. It also means your HVAC is using more energy consistently to keep itself running. Your electricity bill is likely to grow in size from month to month as the problem continues.

Even if you don’t notice the damage to your home, you’re likely to notice how the stack effect impacts your family. Anyone living in the home may run into: 

  • Health Issues 

Derived explicitly from the mold that starts as a result of the stack effect, there are significant impacts on the family members’ health living inside the home. Mold spreads through spores, which often become aerosolized, making family members sick the longer they live in such an area. 

Anyone exposed to mold and its spores is likely to develop different allergic reactions, even if they haven’t had allergies in the past. Some of the most common types of reactions are a runny nose, watery eyes, scratchy throat, fatigue, or even headaches. These problems will only grow in scope the longer there is exposure. 

  • Comfort Issues 

The general comfort of the people living in a home will be impacted if the stack effect is in full swing. Aside from the overwhelmed HVAC and high utility bill, the family’s comfort should matter just as much. No matter the season, the stack effect would make it considerably more challenging to get comfortable. 

For example, in winter, the home continually feels cold and uncomfortable as the HVAC works to bring the temperature to your desired level. The summer would be the opposite, with the HVAC unable to cool the air enough to get relief in the heat.

Innovative Basement Authority Offers Trusted Solutions 

If you live in a home where the stack effect is causing problems, there is no reason to hesitate in contacting Innovative Basement Authority. Serving Minnesota, North Dakota, and eastern Montana areas, all you need to do is reach out for a free quote

Our team of experts can use their 15 years of experience to evaluate your home, with its unique problems, and recommend customized solutions. Ready to start fighting the stack effect and mold growing in your home? We’re here to help.

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