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How Does Your Crawl Space Influence Indoor Air Quality?

Read time: 7 min.
Crawl Space Influence Indoor Air Quality

For most of us, our home is a haven where we spend most of our time. We don’t usually think about the unseen forces lurking beneath our floorboards. You should be aware that your crawl space influences your indoor air quality, which can significantly impact your home’s structural integrity and your family’s health.

The National Association of Home Builders reports that around 12% of newly built homes had a crawl space in 2020. Although slab foundations seem to be taking over, a sizeable percentage of Americans live in homes with a crawl space. Many assume this space is inconsequential, but this is far from the truth, as you’ll soon discover. Crawl space influences indoor air quality and should be a priority for every homeowner with this type of foundation. So, you should investigate to learn if you have this in your home.

Table Of Contents:

How Does the Air From Your Crawl Space Impact You?

Most homeowners don’t realize crawl spaces are not entirely sealed off from the living spaces above. Think of them as a sort of giant lung, constantly “breathing” in the air from outside and circulating it up into the home. We’re talking about up to 50% of the air on your home’s first floor. That’s because warm air rises. This is called the stack effect, and it draws cooler air in from the lowest level of your house as a replacement, almost like a vacuum.

Crawl spaces also collect water that seeps in from the ground or leaky plumbing pipes. Throw in high humidity levels, decaying wood, and even animal droppings; the situation can become alarmingly unhealthy. Here’s a breakdown of the contaminants often found lurking in crawl spaces and the risks associated with them:

  • Mold Spores: Mold grows on pretty much any surface. Mold growth thrives in the darkness and dampness, producing tiny spores. Those spores get carried up into the living areas, often spreading through HVAC duct leaks. Those mold spores, particularly black mold spores, can cause respiratory issues and allergies.
  • Pests and Droppings: Crawl spaces are like a comfy all-inclusive resort for rats, insects, and all sorts of creepy crawlies. Rodents create nests and multiply fast, spreading feces. Rodent urine and droppings carry Hantavirus, which can cause Hantavirus Pulmonary Syndrome. HPS is a serious and potentially fatal respiratory disease with flu-like symptoms that can progress to severe breathing difficulties.
  • Radon Gas: This dangerous radioactive gas forms naturally from uranium decay in soil and rock. This gas seeps up from the ground into crawl spaces. Because it is colorless, odorless, and tasteless, most people have no idea they’re being exposed to it. Radon exposure is a leading cause of lung cancer for non-smokers.

All those toxins swirling around under your house? That is affecting you, probably without you even realizing it. This can impact your family in several ways, depending on the severity of the issue and the sensitivities of your family members:

  • Respiratory problems like asthma and persistent cough. People living in a home with a damp crawl space are much more susceptible to these ailments.
  • Allergies. Ever feel like your home makes you sneeze more than usual? That could be due to dust, mold spores, or other allergens in the air, making allergies flare up.
  • Aggravated symptoms for anyone with underlying health conditions, like respiratory disease. Mold exposure can exacerbate symptoms. It might even trigger an autoimmune response.
  • Musty odor. Sometimes, a persistent musty smell is the only indication that you have a crawl space air quality problem. But never ignore it. There’s a good chance you are inhaling contaminants.

The Importance of Crawl Space Encapsulation

This method works when it comes to addressing the negative influence your crawl space has on indoor air quality. Think of it as putting your crawl space in a hazmat suit. Encapsulation prevents moisture and pests from getting in. It even limits radon seeping in from the soil.

How Crawl Space Encapsulation Improves Air Quality

Most foundation contractors use a three-pronged approach to improving crawl space influence indoor air quality via encapsulation:

  1. Sealing Vents. Those open vents intended for ventilation? They often cause more harm than good. Contractors seal them completely to block the entry of pests, moisture, and humidity. Sealing things up keeps major contaminants at bay while allowing limited natural airflow.
  2. Installing a Vapor Barrier. You want to cover every square inch of the floor and walls. A polyethylene vapor barrier prevents ground moisture from entering. This moisture creates dampness and humidity, which causes mold to form.
  3. Installing a Dehumidifier. Controlling moisture and humidity is a crucial element for any homeowner whose crawl space is affecting the air they breathe indoors. Contractors install a high-powered dehumidifier. This helps control those levels. Often, it’s also tied to the home’s existing HVAC system, creating an energy-efficient closed loop that dehumidifies both the crawlspace and the living areas above.

How To Get The Job Done: Preparation is Key

Encapsulation sounds involved, and it is. It’s best to hire a foundation specialist who understands how the crawl space influences indoor air quality. But you should prep your crawl space for the work to make things go smoothly:

  1. Standing water: It is not only unsanitary but can be dangerous too. Electricians, for instance, will refuse to work around moisture for safety reasons. So deal with standing water ASAP. That usually means calling a plumber and a foundation company to investigate the cause. Maybe you have broken or blocked plumbing under your house. If the moisture on surfaces does not look like a plumbing leak, the foundation expert may suggest additional ventilation or other remediation.
  2. Safety: Clear out anything that might obstruct the work area: rocks, stored boxes, old tools – whatever might be down there.
  3. Wiring: I can’t stress this enough. Electrical problems are not just an inconvenience; they can also cause a fire. Double-check that your electrical wiring isn’t damaged or compromised. This includes wires feeding power into your home. Those damaged wires may need immediate repair.
  4. Other issues: When you go under your house, really pay attention. Take pictures. Then, discuss any questionable spots with your foundation professional. Pinpointing problem areas, like recurring leaks or damaged insulation, can really help direct their inspection.

Health Considerations

This is often overlooked in the building and design phase. Architects, HVAC professionals, and plumbers can easily install piping and ducting in an open crawlspace without hassle. The Environmental Protection Agency (EPA) has identified a real problem – most people are spending an increasingly large percentage of time indoors. Protecting this interior living space from hidden dangers such as those found under a house is essential.

Your crawl space’s influence on indoor air quality goes beyond just impacting your lungs. The EPA tells us that allergic reactions include but are not limited to sneezing, itchy and runny nose, red, itchy eyes, and even skin rashes. While the EPA doesn’t have specific standards for regulating most common contaminants, including those found in a crawl space, that doesn’t mean they aren’t problematic.

What are some of the long-term effects?

Those allergy symptoms could just be the beginning. If mold and contaminants persist long enough, some individuals become increasingly sensitive to their effects. Symptoms become progressively more pronounced. Some effects don’t manifest for months or even years after prolonged exposure to damp and polluted crawl spaces. Chronic respiratory illness, chronic fatigue, and even persistent skin issues have all been linked to crawl space toxins. The worst-case scenario is chronic lung illnesses.

Preventative Measures

Your crawlspace checks out okay? Or are you just buying a new home that already has one encapsulated? Don’t just assume things are great. It’s about what you do to address crawl space influence on indoor air quality going forward because a lot can change even from season to season. Keep these practical steps in mind:

  1. Regular Inspections: An ounce of prevention goes a long way. Go under the house. Check for signs of water intrusion or animal activity at least twice a year. Be especially watchful during the wet or humid months of the year. If your crawl space already has an installed dehumidifier, pay attention to it. Empty any collection tanks or replace drain tubes as needed.
  2. Insulation: Look closely. Deteriorating insulation should be replaced immediately before it starts contributing to mold and moisture problems. Pay close attention to pipe insulation. A little tear or rip in pipe insulation could quickly trigger mold issues because condensation collects readily around cold water pipes. Insulation is also key for keeping heat bills down. Replacing worn or missing insulation on HVAC ducts and hot water lines can really make a difference in keeping energy costs down.
  3. Keep things clean: Treat your crawl space as if it were an extension of your living space. Regular sweeping to remove dust, cobwebs, or stray leaves can limit problems down the road.
  4. Pest control: You should never ignore even minor signs of pest activity because even a few mouse droppings can spread Hantavirus. The EPA gives an even deeper look into how mold exposure can affect you.
  5. Moisture Mitigation: Pay close attention to signs of dampness. Mold starts to grow within 48 hours of excess moisture.

Maintaining a Crawl Space

Here’s a tip: consider making a list or checklist. Attach it to a clip board and store it in the crawl space so you can quickly reference the items you should pay close attention to during your twice yearly visits. You could organize it like a table:

Issue Prevention Steps
Leaks and water intrusion Visually check plumbing pipes and water lines for evidence of moisture and dripping. Look closely for signs of leaks on walls and insulation. Ensure gutters and downspouts divert rainwater away from the home’s foundation.
Mold Growth Remove existing mold with an appropriate cleaning solution and check the dehumidifier for correct operation.
Pest Activity Look closely for droppings and signs of nesting activity, paying special attention to stored boxes or loose insulation. Seal any gaps or holes in the foundation to prevent pest entry.
Insulation Issues Replace missing or deteriorated insulation, particularly pipe insulation.
HVAC Concerns Check the HVAC air filter regularly and replace it as needed to maximize air flow efficiency.


Understanding the invisible threats your home could hold will go a long way toward protecting yourself and your loved ones. Taking practical, common-sense steps now could protect your health for years to come. You owe it to yourself to address the crawl space’s influence on indoor air quality. Do not underestimate its potential effect.

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