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crawl space vent

Crawl Space Ventilation

While it is always a good idea to keep your crawl space well ventilated, we now know that the best methods of ventilation to avoid damage are interior air conditioning systems.

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While everyone agrees it is best to not let air stagnate in your crawl space, the best methods of crawl space ventilation have changed drastically over the last 20 years. Previously, installing exterior crawl space vents to allow airflow from outside was considered best practice for those looking to minimize the chances of dampness and damage in a home. These days, we know that exterior crawl space vents are more likely to cause damage than prevent it.

This is why so many homeowners now have crawl space vent covers and doors installed when they move into a new home. If you have a home with uncovered vents, or you are about to move into one, there are some things that you should know about crawl space ventilation.

The History of Crawl Space Vents

Building codes and the definition of “best practice” can change drastically and quickly. This is because the construction industry is constantly conducting research to find out the limits and benefits of new materials, tools, and processes. Crawl spaces, however, have existed as a kind of no man’s land for both construction workers and homeowners. This is probably because they serve a functional purpose as a space that all utilities pass through but aren’t really a usable space.

Crawl space ventilation has always been somewhat necessary, but the concept of having crawl space vents in place to increase airflow began in the 1950s. The idea was that by allowing air to freely circulate the crawl space, the likelihood of dampness, humidity, and the issues they can bring would be reduced. For this reason, crawl space vents were installed as a matter of best practice until roughly the 1990s. At this point, research found that they not only failed to prevent dampness but actually made it worse. Studies of the stack effect also showed that crawl space vents could impact a whole home.

crawl space vent

What Is the Stack Effect?

The stack effect as a term refers to the process by which external airflow removes conditioned air from a property entirely, drawing in moisture, bacteria, and other contaminants from the outside world. This means that a property with exterior crawl space ventilation can experience several issues that affect everything from the structure of the property to the health of its owner and even the property’s energy usage levels.

This is why it is now considered best practice to cover crawl space vents when they are present. Doing so offers many benefits and seriously minimizes the chances of avoidable dampness and damage within the crawl space and the wider property. This has been considered best practice since the early 1990s but has since come to include wider waterproofing measures.

Why Crawl Space Ventilation is Harmful

We now know that crawl space ventilation is actually harmful to a property—but why is this? First and foremost, uncovered vents leave your crawl space, and thereby your home, open to the elements. This means that your crawl space is affected by the temperature and weather extremes of the outside world (even if it is limited to a degree). As such, things like heavy rain, snowstorms, sudden thaws, and flooding can all lead to water seeping, dripping, or even pouring through the vents and into your property. This will cause obvious issues in both an immediate and long-term sense.

Changes in temperature can lead to plumbing damage. A sudden cold snap, for example, is much more likely to cause the pipes in a property’s crawl space to freeze. This will cause the water inside to expand and can lead to the pipes in question bursting. A plumbing flood will follow the next thaw, and this can be catastrophic for any home.

The real problem with crawl space vents is not the potential for isolated, catastrophic damage, but the ways in which it undermines the stability and health of a property on a day-to-day basis. These issues are caused partly by the stack effect but also by frequent and persistent condensation.

The clash of warm and cool air that occurs in an unsealed crawl space will lead to condensation forming on cold surfaces like stone, wood, and metal. This will not only create a general air of dampness and humidity, but can directly contribute to things like fungal growth, rot, and corrosion. This can cause wider structural damage over time, but will also impact your energy consumption and even your health. As such, it is best to have an exposed crawl space assessed and encapsulated by a professional.

Problem Signs to Look Out for in Your Crawl Space

Learning to spot problem signs of dampness, humidity, and damage in your property and crawl space is something every homeowner should do. As well as allowing you to catch issues before they spiral out of control, these problem signs will help a professional diagnose all underlying issues in a crawl space before proceeding with encapsulation.

Pooling Water

If you have uncovered vents, there are many fairly benign reasons as to why you might find pools of water in your crawl space. That doesn’t mean they are not a red flag. Water will wreak havoc in your crawl space over time, leading to avoidable issues in every part of your home and even impacting your health.

However, if you see a lot of water, there is a chance that the source is some kind of plumbing or foundation damage. Look for steady or visible drips of water around the wettest areas of your crawl space. If you can see steady, consistent drips, it is likely that there is damage to your pipes or plumbing appliances somewhere in the vicinity.

If there are no drips and the water is concentrated away from your vents, there is a chance that some kind of structural or foundation damage is allowing groundwater to seep up into your home. For the safety of your home, you will want to act quickly.

Growing Cracks

If you find cracking getting larger in your property’s foundation walls, support columns, and floors, you should call a professional as soon as possible. These cracks are a sign that there is serious pressure or strain somewhere in your property that is starting to take its toll. These cracks will let groundwater seep into your home, but that is really the least of your worries.

Structural problems are issues that will only deteriorate over time, and if they are left alone for too long they can even lead to the collapse of a structure. Though this is the most serious and extreme outcome, it is more likely that the issues that deteriorate until they cause the structure of your home to become uneven, unstable, and lead to issues like jamming doors and windows. Structural issues will only get more expensive and complicated to fix over time.

Sagging Joists/Floors

If your flooring or crawl space joists are starting to bow, lean, or sag, this is a serious problem sign you should not ignore. This could be a result of deterioration caused by an unhealthy environment (which is most often caused by uncovered vents). However, there are other potential causes.

Defects in the wooden joists, for example, can lead to them deteriorating over time. Likewise, certain kinds of pests and fungal growth can cause enough damage to weaken the joists significantly. Finally, joists can be overspanned because of design faults and miscalculations. Whatever the cause of damage, sagging joists will lead to sagging floors and cause problems over time.

Mold and Mildew Formations

Mold and mildew go hand in hand with dampness and humidity in any space. If you see them, you should investigate. Do so carefully, however, as some species of mold are actively harmful or toxic, especially if you have underlying health conditions.

You will recognize mold and mildew by the texture, color, and even the smell that it produces. Mold formations can vary in color from light grey to pinkish to black or brown, can look or feel fuzzy, and will generally take a rounded, organic-looking pattern of growth. The smell that it produces tends to be slightly musty, dry, or sweet and powdery.

The issues that mold can cause include wood damage, ruined soft furnishings, skin irritation, throat, nose, and eye irritation, migraines, breathing difficulties, and light-headedness. If you have an autoimmune condition, however, the issue could be far more severe.

Pest Infestation

The signs of pest infestation can be varied and surprisingly subtle, but when there are pests in a crawl space, the rest of a property is sure to suffer. The most common pests found in Toledo and Cleveland, Ohio, home include cockroaches, spiders, mice, rats, bees, or wasps. The signs of infestation vary, depending on the type of animal.

However, their general signs include droppings, shed skins, nest formations, eggs, and sightings of the live animals themselves. With things like bee or wasp nests, you will also notice a low-level humming. Closing off your crawl space vents will not prevent infestation altogether, but it will make it less likely.


Rot can take many forms. From dry rot (otherwise called brown rot) and wet rot in wood to deterioration and rot in insulation, there are many different organic materials and surfaces in a crawl space that can start to deteriorate when exposed to the elements.

Brown rot, or dry rot, is most common in wood and is recognizable by the way that the wood seems to shrink, crack, and become brittle. Many say that this looks similar to the way that burned or charred wood looks, simply with different coloring. Wet rot, by contrast, tends to make surfaces and substances look shiny, feel slimy or soft, and even take on a whitish sheen or fuzzy coating.

Rotting insulation will fall away in strips. These strips may be wet and soft or mold-infested. Either way, the smell will be terrible.

Bad Odors
Dry rot

Bad odors are a general problem sign in any area when there is no obvious cause. If you notice a bad smell in your non-encapsulated crawl space, however, you should contact a professional as soon as possible. There is a chance that it could simply be an animal that has passed away (which is unfortunate, but not necessarily harmful to the overall structure of your home), or this can be a sign of wider structural issues.

Bad odors can be a sign of rot, infestation, mold formation, fungal growth, and general dampness. While stagnant water doesn’t have an overpowering smell, it is not a pleasant scent.

If you notice any of these problem signs in your crawl space, you should prioritize a professional inspection as soon as possible. In fact, you should also schedule an inspection before encapsulation, even if you think that your crawl space is healthy. It is far better to be safe than sorry.

Crawl Space Ventilation


If a recent foray into your crawl space has uncovered dampness or flooding, it is natural to be worried. There are a number of issues that can lead to standing water in your crawl space, but the most common (other than open vents) are:

Internal Leaks

One way in which a lot of moisture can make its way into a crawl space is via internal leaks in the plumbing system that runs through a property and its attached appliances. For example, small leaks caused by weak joints between pipes or pipes and appliances can produce a surprising amount of water in any crawl space. A more dramatic example, however, is a bursting pipe.

Plumbing leaks can be caused by a number of factors, but they are fairly easy to spot. Plumbing floods and burst pipes are the most serious issues, and the easiest to spot. You can recognize smaller leaks, however, by sudden changes in water pressure, small fluctuations in temperature, stains around impacted pipes and appliances, and a visible leak.

Structural Damage

Structural damage is a slightly more insidious and worrying cause of dampness and water in a crawl space. The most likely cause of large amounts of water in a crawl space (when open vents and internal leaks have been ruled out) is foundation damage. Any kind of cracking or damage in a foundation will allow a surprising amount of groundwater to seep up into a property.

The most likely foundation issue at work in these cases is settlement. Generally caused by expansive soils, settlement sees sections of a foundation breaking away and sinking into the ground. When rainfall saturates the soil, this will let water seep into the crawl space quite quickly. Another possible cause is subsidence.

Dealing with an exposed crawl space can take a number of forms.Preventing damage is ideal, but when it has already taken root, there are repair methods available.

Structural Repairs

Structural repairs will always take precedence when there is a professional involved. In fact, they should always take precedence over waterproofing measures and cosmetic repairs. That’s because if they are not completed before these processes, the issue could recur or grow in severity and scope. This will make the situation more dangerous and could increase repair costs overall.

Structural repairs cover a broad number of processes including foundation repair, concrete lifting, joist repair and replacement, and wall reinforcement. The nature of structural repairs required in each home will vary depending on a number of factors. This is why we recommend that you call in a professional as soon as possible.

Waterproofing and Encapsulation

If there are no structural repairs needed or the structural concerns have all been resolved, a professional will most likely suggest crawl space waterproofing or encapsulation. This will include covering exposed vents and crawl space access doors but goes much further and has many tangible benefits for your whole home.

Like structural repairs, encapsulation varies from home to home and is tailored to the confines of a specific situation. Generally speaking, however, structural repairs include drainage assessment and improvement, insulation, and the installation of a vapor barrier, as well as the covering of vents and doors. This will improve energy efficiency, reduce humidity, and even allow you to use your crawl space for storage. 

If you have recently moved into a home with an exposed crawl space, or you are ready to consider encapsulating the crawl space of your current family home, we urge you to contact a crawl space specialist.

The Dangers of DIY

DIY repairs are something that many homeowners dabble in, and while we agree that it is good to have basic DIY skills, we also believe that DIY should end where structural issues begin. Because there is a high likelihood of structural problems in a damp, wet, or unhealthy crawl space, we urge our clients to avoid DIY encapsulation.

If you simply waterproof and seal a crawl space that is being affected by things like foundation damage, all you will be doing is covering up the signs of deterioration. This will lead to the issues being far more advanced when they are discovered. Worse still, you could end up creating an incubator of sorts, trapping water and pests into your crawl space. This could actually cause more damage than was previously at work.

The Benefits of Professional Services

A professional service offers many benefits, but the most obvious is its ability to safely and effectively tackle structural issues. Foundation damage, in particular, is quite dangerous when it comes to DIY repairs. This is because of the way in which it destabilizes many other parts of a structure. If you try to go it alone, you run the risk of causing damage or injury.

Furthermore, these tools are specialist in nature. Most homeowners will not have them to hand. By the time you rent all the necessary equipment and buy the required products, you could well end up paying more for a lower quality result if you try DIY. An expert will have all these tools already and can guarantee a certain standard of results. Finally, professional services offer permanent solutions. This is something you cannot guarantee if you try to undertake repair and encapsulation alone.  

Choose Ohio Basement Systems for Crawl Space Encapsulation

Whether you have noticed signs of dampness and damage around your home, or you are simply concerned about the open vents in your crawl space, Ohio Basement Systems is here to help. Our team of qualified specialists has been helping homeowners across Toledo and Cleveland, Ohio, since 1999, building a reputation for excellence that cannot be denied.

If you want to know what we can do to improve the health of your home, do not hesitate to contact us directly to book your free inspection appointment. These appointments come with no obligation to book an encapsulation through us on that day, or at any point, and will include a written estimate for all of the costs associated with the work that we are suggesting.We give this to you to help plan for your appointment and make an informed choice about what is best for you.

Contact our Crawl Space Experts today!

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