How to Improve Basement Air Quality

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Written By Jamila W.

The basement of your property is the most vulnerable area of your home to poor indoor air quality. Many property owners are familiar with the dank and musty smell, dust mites, and close conditions that make breathing in a basement space uncomfortable. If you intend to occupy your basement as a living or working space, you must address basement air quality to protect your health and prevent the spread of air pollutants throughout your home. 

In this article, we explain why basement air quality deteriorates and 8 key steps you can take to improve it. 

Air Quality in Basements

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Basements, cellars, crawl spaces, and other subterranean spaces are known for their dank and musty microenvironment created by wide-ranging biological and chemical pollution sources. They are an integral part of a residential building and directly communicate with the upper levels of a home. If the indoor air quality of a basement is poor, it can affect the other areas of a home. In addition, many basements are converted to create living spaces or complete dwellings where occupants are exposed to basement air for prolonged periods, often with inadequate ventilation.

Factors Affecting Basement Air Quality

Common factors that affect the air quality of a residential basement include

  • Raised indoor humidity relative to the rest of the property.
  • Cooler temperatures because the room is subterranean.
  • Poor ventilation and air exchange, because of limited access to outdoor air.
  • The development of mold and mildew, because of reduced air movement and cooler temperatures causes water vapor to condense on surfaces.
  • Little or no sunlight due to the underground location.
  • Unsealed or poorly insulated flooring and walls can degrade and shed dust.
  • Items in long-term storage, including furniture, paints and household chemicals, or root vegetables, preserves, and pantry items. Studies have shown that up to 75% of basements contain sources of harmful air pollutants like volatile organic compounds, especially if items are old or degraded. [**]
  • The accumulation of house dust from stored items, unfinished walls and flooring, and human occupation and activity. [*]

Poor Air Quality Is Behind ‘Basement Smell’

These factors lead to many basements developing characteristic musty odors known as basement smell. This odor is driven by the raised indoor humidity and dampness of basements with the putrefaction of any biological material by microorganisms in the environment. The air pollution in basements is often predominantly microbial, with high concentrations of mold spores and bacteria suspended in the air that are inadequately ventilated releasing musty odors that persist in the indoor environment.

If basements are occupied for a prolonged period, without tackling the basement’s air quality or problems like high humidity, occupants can be affected by wide-ranging symptoms and health conditions related to indoor air pollutants. Symptoms like headaches, fatigue, and breathing problems are driven by organic pollutants like VOCs, from building materials and paint that cannot freely escape through windows or ducts. 

Air Exchange in Basements

The pollutants that accumulate in basements lead to basement air routinely having higher concentrations of pollutants than indoor air. These pollutants are often transferred into other parts of the property where they diminish IAQ in living and sleeping spaces. U.S. research studies have shown that air is not only exchanged between a basement and living areas in a property, but also the rate of this air exchange is higher in the winter than in the summer. [**] Basements have also been shown to have higher concentrations of VOCs than other areas of a home, probably due to the storage of solvents and equipment like gasoline generators, potentially leading to the increased migration of VOCs to other areas of a home. 

A Toxic Mix

The range of air pollutants in basement air is also extremely diverse. Studies that have identified and measured the concentration of basement air pollution have found noxious substances that include:

  • Pentane
  • Pentanal
  • Hexanal
  • Formaldehyde
  • Acetaldehyde
  • Benzene
  • Toulene
  • Naphthalene
  • Methylene chloride
  • Chloroform
  • Trichloroethene
  • Butadiene

The concentrations of these VOCs in basements can become extremely high in the summer months because of the storage of gasolene-powered garden tools that are being actively used, and the storage of gasoline, diesel, and synthetic oils. 

Radon Is Also a Concern

The proximity of basements to the soil makes radon ingress and accumulation in basements a serious concern. This radioactive gas, released from uranium deposits in the earth, is heavy and can achieve high concentrations in indoor air by settling in basements. Without efficient ventilation exposure, this odorless and colorless gas raises the risk of developing lung cancer. A professional radon test can identify if there is a problem with this radioactive odorless gas in your property.

Health Consequences of Poor Basement Air Quality

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The diverse pollutants in basement air not only cause a bad smell but also can precipitate or aggravate a range of acute and long-term health problems including:

  • Rhinitis
  • Heart disease
  • Hypertension
  • Chronic Obstructive Pulmonary Disease
  • Asthma
  • Lung cancer

How to Improve Basement Air Quality

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A strategy for improving basement air quality has to be multifaceted and address each of the contributing factors to poor IAQ with professional assessment and remediation where necessary. This is particularly important if the basement is being renovated and will be used as a living space. Here are eight key areas that need to be addressed for a sustained uplift in indoor air quality in a basement:

1. Seek Professional Radon Testing

The Environmental Protection Agency recommends professional radon testing if a basement is going to be occupied for a prolonged period on an ongoing basis. As the lowest lived-in level of a property, it is the area where radon exposure will be highest. Ideally, radon testing should take place before any remodeling of the basement to avoid costly remediation work, including having a mitigation system installed, after the basement is finished. An experienced technician will be able to identify key points of radon entry like cracks, drains, sump wells, and foundations. They will also advise on strategies to prevent further ingress like ventilation, sealing, or room pressurization.

2. Upgrade Basement Ventilation

Increasing ventilation is a priority for basements but their subterranean location naturally limits the opportunities and infrastructure for achieving this. If a basement is to be excavated or renovated there must be a robust strategy for integrating mechanical ventilation that ideally extracts indoor air rather than allowing the ingress of outdoor air which can promote mold and mildew. 

3. Install or Replace Basement Windows

Windows allow in natural light and increase the opportunity to ventilate a basement. However, the air that enters basements from outside tends to be moisture and mold-spore-laden, especially if there is a temperature gradient, so windows should not be relied on as the primary means of ventilation. 

Old basement or crawl space windows from homes built before the 1970s may have lead paint in their frames that can lead to the release of lead dust into a home. If possible, choose ENERGY STAR-rated windows that are less likely to cause condensation and the development of mold. 

4. Control Moisture

Moisture is a big contributor to poor air quality in basements as it promotes mold growth. Moisture problems in basements can quickly become pervasive and start to affect other areas of the property, so it’s important to thoroughly inspect the basement for dampness, high humidity levels, leaks, mold, and other sources of moisture. 

Internal and external sources of moisture should be corrected like downspouts that are draining water towards the basement, the poor venting of a clothes dryer, waterproofing walls, or installation of a membrane system. A portable dehumidifier may also help to improve indoor air quality by removing water vapor from the air indoors. Dehumidifiers can be run continually as they have an air quality monitor that measures humidity levels and adjusts the performance of the unit.

5. Ensure Any Gas or Combustion Appliances Are Working Properly

Combustion appliances like furnaces are often located in the basement of a property. They are a potential source of harmful airborne particles and poisonous carbon monoxide (CO) gas. Arrange professional HVAC assessment of combustion equipment to ensure that it burns fuel efficiently and is properly vented and obstruction-free. A CO alarm should be installed in the basement to alert occupants to raised CO levels.

6. Address Basement Flooring

The flooring of a basement is also a key source of moisture mold and mildew problems, or masonry dusts that deteriorate air quality. One of the big issues with flooring in a basement is that it is installed on a porous concrete slab, allowing moisture to penetrate and rot the flooring materials. Concrete slabs are also cooler and promote condensation and the growth of mold spores on carpets. If there is a chronic moisture problem the floor should be raised and carpet would be avoided. 

7. Address Removable Sources of Air Pollution

After addressing the structure of the basement, you can look for sources of pollutants that can be removed or sealed in the basement to prevent their ongoing release and accumulation in the air. Here are some common basement air pollutants you can address:

  • Asbestos: If you have concerns that there may be asbestos present in the basement, it is important to get suspect materials professionally tested and undertake asbestos abatement where necessary. 
  • Volatile Organic Compounds include poisonous air pollutants like benzene, formaldehyde, and toluene. These noxious chemicals can be found in gasoline, engine oil, paints, solvents, and weed killer. If these items are stored in the basement, removing them will improve air quality. 
  • Biological air contaminants: Sources of airborne microbes include infestation, rotting foodstuffs, and mold. A basement or root cellar should be cleaned regularly if food stuffs are being stored, to prevent the spread of bacteria and mold. 
  • Dust: Regular cleaning helps to reduce the level of dust which can become a vector for mold and odor in the basement. 

8. Use an air purifier to cleanse basement air

If a basement is occupied on an ongoing basis, air purifiers can help to keep down levels of common allergen particles and gaseous air pollutants, making the air safer to breathe. Air purifiers work best when the underlying causes of indoor air pollution have been addressed and sources of pollutants have been entirely removed, but they are one of the most effective solutions for the basement odor that accumulates due to stagnant air. Several classes of air purification technology target specific types of air pollution in basements. Key classes of air purifiers include:

  • Fibrous filter media: These air purifiers have fibrous filters that trap particulate air pollutants using mechanical, fan-based filtration. HEPA filters, an industry standard for fibrous filters, can trap particles as small as 0.3 microns with 99.97% efficiency.
  • Electrostatic precipitation (ESP): This air purification technology targets particles and some organic gases using electrostatic forces generated by electrically charged plates.
  • Chemisorbent media: Air filters are coated in materials like activated carbon filters that chemically trap and retain organic and non-organic gasses. This is the most-effective air purification technology against odor.
  • Catalytic oxidation:  This is a particularly effective air cleaning technology that can destroy particulates and gasses in indoor air using ultraviolet light and a titanium dioxide catalyst. 

In Conclusion

Managing air quality in your basement is essential for the protection and breathing comfort of occupants. Basements are affected by a wide range of biological, organic, and inorganic pollution sources. Their unique microclimate, due to their location, limited ventilation, and temperature differences makes it easy for pollutants to build up and cause harm. After addressing the key causes of poor air quality in your basement, an air purifier is essential for keeping pollutants at bay and reducing the musty odor that can easily return.