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Open Vents

Open crawl space vents are a known cause of dampness, humidity, and generally poor health in a property’s crawl space. Here’s what you need to know.

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Between the 1950s and 1990s, many homes across Indiana, and the U.S. as a whole, were built with crawl space vents as standard. This was considered best practice at the time because professionals believed that increasing airflow inside a property’s crawl space would minimize the chances of dampness and humidity from impacting the space. Crawl space vents do increase airflow in a property, but the problem is that this is not as beneficial as many people believed that it would be. 

Here’s what you need to know about open vents and the damage they can cause in your crawl space

Open Vents and the Stack Effect 

crawl-space condensation

Open crawl space vents contribute directly to the formation of the stack effect in a property. The stack effect is a process that disrupts the climate of a whole property very quickly and causes serious damage over time. The stack effect requires ventilation points at both the top and bottom of a property in order to take full effect. 

How Does the Stack Effect Work? 

The stack effect is essentially a process that relies on the pressure changes in the air as it is processed by a property’s HVAC system. Hot air is lighter than cold air, which is quite dense—in a property that has a neutral pressure level, meaning that the pressure inside and outside the property is the same, the hot air rising will not make much difference, as it will have nowhere to go. This is how your HVAC system is able to fully heat your home. 

When there are opposing ventilation points, the artificially heated or cooled air will be pushed out of the vents, drawing in air from the outside. For example, during winter when your HVAC system is heating the air in your property, that hot air will rise and escape through the roof ventilation points, drawing in cold air at the bottom of your home. By contrast, when your air conditioning system is cooling air in the summer, this cold air will sink and exit via your crawl space vents, drawing in warm air from above. 

This makes it very difficult for your property’s HVAC system to effectively control the temperature and climate in your home. As a result, it will have to work much harder and may deteriorate quicker. This can lead to avoidable damage and breakdowns and will lead to a general decrease in energy efficiency. 

The Damage Open Vents Can Cause 

Thanks to the stack effect, open vents in your crawl space can cause many different problems and kinds of damage in your home. Most of them are connected to dampness and crawl space humidity in some way, or result from the effects of dampness because open crawl space vents primarily cause condensation and allow water to invade a crawl space. The damage that can result from this includes: 

Mold and Mildew 

Mold and mildew are unfortunately common in crawl spaces across Indianapolis, Indiana, because of the climate. Mold requires three things to form and spread: moisture, organic material, and spores. This makes your crawl space the perfect space for mold growth, especially because it is so rarely traversed by anyone. 

As well as smelling bad, mold can cause damage to your home and have an impact on your health. This is because mold eats away at organic surfaces, especially those which are dealing with wet rot or other forms of damage. Because mold spores are airborne, the stack effect will also spread them through your property. This can have a huge impact on your health, especially if you have black mold. 

Black mold is one of the few actively toxic mold species that can take root in your home. Black mold can cause headaches and migraines, dizziness, breathing problems, skin and eye irritation, and even bacterial infections. If you have any underlying health conditions, especially ones that impact your immune or respiratory systems, the implication of black mold can be far worse. 

Wet Rot 

Wet rot is fairly easy to spot because it changes the look, texture, and smell of anything it affects. The most worrying kind of wet rot in a structural sense is that which affects wooden surfaces. The support joists and beams in your crawl space, for example, as well as the wooden floorboards and any drywall in your property, are vulnerable to this and will suffer if it starts to affect them. 

Wet rot will make these surfaces look and feel slimy, and may impart a white-ish sheen on their surfaces. It will also weaken them and give them a soft or crumbly texture. As a result, this can lead to them falling apart or collapsing entirely, taking down any structures that are reliant upon them. 

Pest Infestations 

Pests are attracted to the environment in a crawl space, and open vents provide them a very convenient point of access, as well as contribute to the kind of environment that is very welcoming to them. The most common pest infestations in and around Indianapolis, Indiana, are cockroaches, spiders, rodents, and termite infestations.  

Rodent infestation is one of the most unpleasant for many people because of the droppings they leave, the smell of urine that they cause, and the visible presence of rats and mice in many cases. That said, rodents are actually less harmful than cockroaches in many senses because cockroaches are so notoriously unhygienic and can get into every part of your property very easily. Termites are the most likely to cause serious damage to your home, however, and can decimate huge amounts of wood in just a few months. 

Cosmetic Damage 

The dampness and humidity caused by open vents will also cause cosmetic damage throughout your property over time. This can take many forms, including discoloration, bubbling or peeling wallpaper, pitting or flaking concrete, and staining on your fabric furnishings or surfaces. 

Sagging Floors 

Sagging floors are often a tertiary issue that forms after wood rot has impacted the joists and beams that support your home’s main floor. This will first start as bounciness and springiness underfoot and will develop into a noticeable and visible sag. 

Once the floor has started to sag, it will eventually pull away from the walls that it should be attached to and lead to gaps between your floor and walls. This will increase airflow and exacerbate the effects of the stack effect in your home. 

Above and beyond these issues, open vents and the stack effect will impact the climate in your home as a whole. The dampness and mold that so often go hand in hand will produce a bad smell that can permeate your whole home. This will make your internal climate changeable, unpleasant, and unhealthy as well as increase your energy bills, but if you catch these issues early, you will have a chance to avoid the worst of the damage.

sagging floors in crawl space

Signs of Damage To Look For 

These problem signs are some of the most obvious signs that you have damage in your property that may have been caused by open vents and dampness caused by an ongoing stack effect. These signs can also be connected to other problems, so please contact a professional to ensure the issues are dealt with appropriately. Here are the most serious warning signs. 

Pooling Water or Flooding 

Pools of water in your crawl space, or outright flooding, is a serious issue that is both symptomatic of a problem and likely to cause lots of extra damage. If you have open vents in your crawl space it is very likely that the source of the water is outside of your home. However, this is also a chance that there is an internal leak in your home’s plumbing system somewhere. 

Bad Odors 

If there is a sudden and persistent bad smell in your property that will not go away even when you deep clean and air your property well, the most likely cause is going to be open crawl space vents and some kind of fungal or bacterial growth, or even rot as a result of dampness and humidity. Whatever you do, don’t ignore that bad smell. 


There are times when condensation is perfectly normal. For example, condensation is common in bathrooms and kitchens when they are in use because of the steam that is often found in these areas. Likewise, you may sometimes see condensation on your windows. If you find condensation on your walls, however, or in your crawl space, this is a sign of serious issues with dampness that you should not ignore. 

Increasing Energy Bills 

Energy bills can go up and down based on a number of factors, which makes them fairly hard to keep track of. An abnormal rise in your bills, however, is something that you should not ignore. If you feel that your bills are rising you can check them against bills from the same period the year before. Just remember to consider things like how many people are at home, how often you use your HVAC system, and whether you are in the house for more of the day than usual. If everything is much the same but the cost of your bills has risen, you should call a professional. This can be caused by excessive humidity or HVAC deterioration and breakdown (among other things). 

Fluctuating Temperatures 

A healthy, well-insulated property should not experience frequent or dramatic fluctuations in temperature. If this happens, you can be certain that something is destabilizing the climate in your home. As such, it is important that you act quickly and nip it in the bud. This will make your home more comfortable, and also increase energy efficiency. 

If you see more than one of these signs in tandem and you notice that you also have open crawl space vents, please contact a professional quickly to undertake repairs and encapsulate your crawl space. 

Open Vents


One of the things that makes many people wary of covering their open vents is the matter of access to their crawl space. Thankfully, there are many options open in this regard. 

Internal Access 

Covering your crawl space vents and doors does not seal your crawl space away forever. Most properties have access hatches inside the structure somewhere to ensure that the crawl space, and all of the important wires and pipes it acts as a hub for, are always easy to access. If you do not know where your internal access hatch is, you can consult your property’s floor plan. 

If this doesn’t help you, contact a professional, as they will be able to tell you where most access hatches are located on the inside of a property. If all else fails you can also install an access point inside your home. While this extra work may not be quite what you had in mind, covering your vents is absolutely for the best in the long run, and this makes it more viable in some cases. 

External Access 

Alternatively, you can invest in crawl space doors rather than vent covers. These act in the same capacity as covers by sealing your crawl space away, but they have the added benefit of making external access possible when needed. This is perfect for those who prefer to access their crawl space from outside or whose internal access point is in a place that makes it hard to access while carrying tools or replacement appliances. 

These are manufactured to the same standards as crawl space vents and provide the same level of protection, although they should receive more regular maintenance to ensure the seals around the doors have not started to wear away or deteriorate. This is the only real weakness crawl space doors have when it comes to keeping dampness and the stack effect at bay. 

Yes, waterproofing your crawl space at the same time as sealing your vents is very beneficial in a lot of ways. In fact, many feel that it is an absolute necessity. 

Don’t Just Seal Your Vents 

While many people are tempted to simply seal up their vents and be done with it, this can be incredibly damaging to your home. Sealing up your open vents may prevent the stack effect from continuing to impact your home, but if you have any issues with dampness and humidity in this space you will soon see the negative effects of the lack of airflow. 

This will allow water in your crawl space to stagnate and mold to spread at an increased rate. Furthermore, if the water is actually coming from a point of structural or internal damage, the water will just keep building up in your crawl space. So while sealing your vents is a good idea, it is important to remember it is not a cure-all. 

Waterproofing Makes Your Home Healthier 

Investing in a process of waterproofing as well as sealing your crawl space vents will improve the health of your home as a whole drastically. This is partly because professionals will deal with underlying damage before they even start waterproofing, but also because of the benefits of waterproofing itself. 

Waterproofing your crawl space will not only lower humidity levels and prevent the stack effect from impacting your home, but it will also improve air quality, increase energy efficiency, keep mold and pests out, and even allow you to use your crawl space as a storage area if you want. So as you can see, waterproofing your crawl space is a real investment. 

No, you should not waterproof your crawl space or seal open vents without professional help. There are a number of reasons as to why this is the case. From the potential for injury to yourself or extra damage to your home, it is not always easier to go it alone. 

Damage and Injury 

The problem with simply rushing ahead to seal your crawl space off is the likelihood of covering up damage or trapping dampness, mold, and pests inside your home. This will actually make the impact on your property as a whole worse because it will create an incubator of sorts in your crawl space. Likewise, if there are structural issues or toxic forms of mold in your crawl space you could make the damage worse or even injure yourself by trying to go it alone. 

Professionals have the right tools and skills to deal with all underlying causes and co-occurring issues that might be impacting your home safely and efficiently. They will provide you with a high-quality, durable result that protects your whole home. 

Structural Issues 

One of the main reasons why we recommend that you do not try DIY is the chance that structural damage has occurred within your home. Whether the issue is a sagging floor or there is actually a deeper issue contributing to the unhealthy environment (such as foundation damage), it is far better to bring in someone with experience. 

Foundation repair is dangerous, complex, and prone to going wrong when the people involved lack the right tools or training. Furthermore, if you consider the cost of buying products, hiring equipment, and potentially having to replace some things as a result of accidental damage, professional services can be much the same cost. 

Call Indiana Foundation Service for Crawl Space Repair 

If you have noticed signs of dampness and damage in your property or your crawl space is starting to give off some strange smells, Indiana Foundation Service should be your first port of call. Our skilled and experienced team is here to help no matter what problems may be at work in your home. From foundation problems to pest infestations, we have seen it all. If you want to know what we can do for your home, please call us or book your free inspection appointment online

We will schedule this appointment for a time and date that suits you and send a skilled and knowledgeable technician to your home. They will assess your property in full to identify the issues that need to be addressed and diagnose their underlying causes. They will also provide you with a tailored repair plan and a written estimate for all costs associated with these repairs. This way, you can make an educated decision with all the information you need. 

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Foundation Repair, Basement Waterproofing & Crawl Space Repair and Encapsulation, Serving Central Indiana & Indianapolis

Indianapolis, IN

624 North Front Street
Whiteland, IN 46184