The Stack Effect: Understanding Air Quality

Before delving into the reasons for the stack effect or the ways in which it can impact you, there’s a simple question to ask first. What is the stack effect in the first place? Here’s a brief primer on what the stack effect is and how it might impact you.

Entrances and Exits

The first thing the stack effect needs is an entrance and an exit. The stack effect happens where there’s an entrance for air in the crawl space or basement and an exit for air in the attic. Almost all attics have an exit for air of some kind, even if it takes a bit of time for it to go through the pathway. That means the problem usually rests with crawl space vents.

When you have an entrance and an exit for air, you’re usually going to end up with the stack effect. This can even be a problem in one-story homes, where the air doesn’t have to travel very much. These entrances and exits are an important part of the stack effect and removing them typically helps.

Warm Air Rises

The second important thing that drives the stack effect is the fact that warm air rises and cool air sinks. This is true regardless of the temperatures of the air; it will automatically rearrange itself so that the warmest air goes to the top and the coolest air goes to the bottom. If the cool air is on top of the warm air, the warm air will move upward through space.

When air enters the crawl space through crawl space vents, it’s either going to be cooler than the surrounding air or warmer than the surrounding air, depending on the weather. If it’s cooler, it will stay in the crawl space for some time, then warm up, rising through the living area and exiting through the attic. If it’s warmer, it will start to rise through the living area as soon as it enters the home.

Tiny Airborne Particles

What’s the big deal with the stack effect? Aside from the fact that it brings in air from the outside, which might include all manner of things, it’s important to note that it’s not just air that’s coming up through the home. The air might include tiny airborne particles it picked up from whatever’s happening in your home’s crawl space.

Many types of particles can become airborne. Mold spores, dirt, dust mites, pest droppings, and many other types of particles are small enough for the air to pick them up. When that air sweeps through your home, those airborne particles are also sweeping through your home, spreading them across your living space. More than 50 percent of the air you’re breathing in your home comes from the crawl space, so whatever is in this area under your house also is in the air circulating throughout the rest of your home and affecting you.

The stack effect isn’t just annoying; it has some genuine problems associated with it. Although this isn’t a comprehensive list of the health and wellness problems from the stack effect, they’re definitely some of the most common.

Allergic Reactions

Far and away, the most common health problem you might encounter because of the stack effect is an allergic reaction. That’s because many people have allergic reactions to things like dust, mold spores, and insect droppings, which are all things that can rise up into your home because of the stack effect.

Allergic reactions can range from extremely mild to worryingly severe. You might have anything from a general runny nose and cough to serious trouble breathing. Regardless of how severe your allergic reaction is, it’s not great to live in a state of constant allergic reaction. You should remove the source of the allergies, which in this case would be the stack effect.

Mold and Mildew Through the Home

When the stack effect causes air to rise through the home, it also brings airborne particles with it. Mold spores are typically small enough to become airborne, and that means they’re probably going to rise throughout the home. As they do, they’ll scatter all across your home, landing in some cases in areas that can grow mold very effectively.

Technically, mold and mildew require high levels of humidity to grow. However, if you’re dealing with the stack effect, that means you almost certainly have high levels of humidity because you have open crawl space vents. More than likely, no matter what you do, you’re going to be scattering mold and mildew spores all through your home because of the stack effect.

High Energy Bills

The last problem is one you probably haven’t thought much about in the past. High energy bills are a serious concern that many people deal with when they have open crawl space vents. In fact, an Advanced Energy study has shown your energy bills may be 15-25% higher than they should be, just because you have open crawl space vents. If you’re experiencing the stack effect, you’re going to have higher energy bills.

The open vents in your crawl space are definitely annoying, but they’re also costing you money. In this situation, it’s almost always better to invest the money in an expert who can help you with your crawl space woes. A crawl space encapsulation should be able to save you enough money that it’ll eventually pay for itself.

When it comes to reducing the stack effect, there’s really only one thing that will cut the stack effect off at the source. You need to encapsulate your crawl space. After all, if there’s nowhere for air to come into the crawl space, you can’t have the stack effect in the first place. This is the process a crawl space expert will use to encapsulate the crawl space.

Remove Standing Water and Fix Leaks

First up is the process of removing any standing groundwater in the crawl space and any places water might be leaking into the crawl space. Standing water is a terrible thing to have in your crawl space because you’re inevitably going to have extremely high levels of moisture as the water evaporates into the air.

Leaks are the most common reason you might have standing water in your crawl space, but they’re far from the only reason. You might have standing water in the crawl space because your crawl space isn’t graded correctly, because of open crawl space vents, or many other possible causes. Fixing the leaks should be the first thing you do in your crawl space to avoid this exact problem.

Close Crawl Space Vents and Doors

After you’ve removed the standing water in the basement, it’s time to close the crawl space vents and make sure all the doors have effective seals. If there’s no way for air to move into the crawl space from the outside, you won’t have to deal with the stack effect at all. That means the best way to avoid issues that often arise from the stack effect is to close off the crawl space vents and install additional insulation to ensure there’s no way for air to move in.

There are a number of ways to seal crawl space vents and doors to make your crawl space function more effectively. Typically, that means adding crawl space vent covers to any open vents you have, then either installing new doors or adding additional insulation measures to the crawl space doors you have. This can be a very involved process, and it’s important to get a crawl space expert to help.

Install a Vapor Barrier

Next, especially if you have a dirt crawl space, you need to install a vapor barrier under your home. A vapor barrier does what it sounds like: It forms a barrier against water vapor. When you have a dirt crawl space, water vapor is inevitably going to rise through it. This is the case even if the top layer of the dirt seems dry. Dirt crawl spaces connect to the earth far underneath the crawl space, which retains moisture even if the rest of the dirt is fully dry.

However, a high-quality vapor barrier ensures the crawl space stays dry even if the dirt is completely soaked through with moisture. When you have a suitable vapor barrier, you no longer have to worry about any water vapor coming in through the crawl space floor. JES only uses the 20-mil CrawlSeal™ vapor barrier. Although these are thicker than the traditional vapor barrier thickness, JES uses them because of the idea that the crawl space should be overly protected rather than under-protected.

Add a Crawl Space Dehumidifier

The last step is usually to add a crawl space dehumidifier. Even if you’ve completely blocked off the entrances for crawl space humidity, that doesn’t necessarily mean your crawl space will stay at a healthy humidity level. Some locations just have naturally high levels of humidity. Those naturally high levels of humidity will still have a significant impact on your crawl space, which is why it’s important to adjust them.

Instead of just allowing the crawl space to become heavily moisture-laden, you might want to install a crawl space dehumidifier. A dehumidifier allows you to keep the crawl space at a certain relative humidity, which you can keep to a healthy level. Although this isn’t necessary for everyone, it’s useful if you want to maximize your crawl space health.