Indoor Air Quality and Changing Outdoor Environments

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How Can Changing Outdoor Environmental Conditions Affect the Indoor Environment?

Most people in the United States spend about 90% of their time indoors where indoor air quality can be impacted by many factors, including people’s activities, how the building is used, its age, design, construction, operation and maintenance, and outdoor air quality. Changing environmental conditions outdoors can worsen indoor air quality, other indoor environmental issues and occupant health. In some cases, changing outdoor environmental conditions can introduce new indoor environmental concerns.

Outdoor air can enter and leave a building by infiltration, natural ventilation, and mechanical ventilation. In a process known as infiltration, outdoor air flows into buildings through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors. In natural ventilation, air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between indoors and outdoors and by wind.

Most U.S. homes and buildings today are not new and were built to withstand environmental conditions at the times they were built. Methods of ventilating buildings and maintaining acceptable thermal conditions can be included in building design or modification strategies to help adapt to evolving outdoor conditions while maintaining indoor air quality.

Variations in environmental conditions outdoors can affect the indoor environments and occupant health in many ways. For example,

  • Rising ambient pollutant levels and warmer temperatures can over time increase or change the types of outdoor airborne allergens which can infiltrate into indoor spaces and potentially impact asthma, allergies and other occupant health concerns. 
  • Some areas may experience higher temperatures and less precipitation, resulting in more droughts and wildfires. This can result in more particulate air pollution, such as dust and smoke. The particulate air pollution can enter buildings and homes, affecting lung and heart health of occupants.
  • More frequent and longer outdoor heat waves can result in higher indoor temperatures potentially leading to increases in heat-related illnesses.
  • Variable environmental factors can increase precipitation, frequency and severity of storms and weather events, increasing the risk of flood and dampness indoors. This can result in damage to buildings and allow water or moisture to enter indoors creating a perfect environment for indoor mold growth.
  • Changing outdoor conditions can lead to increases in indoor dampness and humidity. These conditions can lead to increases in pests, dust mites, mold, bacteria, and other biological contaminants indoors. Exposure to indoor mold and other biological contaminants can lead to respiratory and other health problems for occupants. Increase in mold, bacteria or other pests indoors can also lead to increased indoor exposure to toxic chemical products to combat infestations.
  • Extreme weather events can increase power outages which can make it more difficult to maintain comfortable and healthy indoor temperatures and indoor air quality.
  • Variations in outdoor environmental conditions can affect building operations that can impact IAQ.  In winter, occupants often close windows and increase use of heating which can reduce ventilation in a building and cause levels of some indoor pollutants to buildup. More people are weatherizing (sealing and insulating) their homes and buildings to offset outdoor temperature changes and to help save energy by reducing the need for heating and cooling changes which without maintaining proper ventilation can negatively affect indoor air. 

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Tips to Help You and Your Home Withstand Weather Extremes and Maintain Indoor Air Quality

Make an emergency plan

Electric power outage

  • Plan for an alternate power source: Consider how to provide electric power safely if floods, high winds, ice storms or other weather events result in power outages. 
  • Plan for an alternate shelter: Include a backup location where you know there will be power, and you will be welcome as part of your emergency plan for power loss.

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High winds

  • Improve the wind resistance of your house:
    • Roof: Small changes can improve the wind resistance of your roof. Roofs are the most exposed part of the house and typically experience the most damage during high winds. High winds can damage the gable end walls and overhangs or lift the roof off the walls. Consider options to secure the roof to the house frame such as adding roof ties downs.
    • Windows: Consider options such as adding shutters.
    • Garage doors: Consider reinforcing double-width garage doors.

Heavy rains

  • Direct water away from your home:
    • Add gutters and/or maintain gutters: Keep gutters and down spouts free of debris and leaks. Direct downspouts away from the house.
    • Slope ground away from building: If rain puddles against the foundation after a storm, correct the problem by regrading the area or installing underground drainage.

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Heavy snowstorms

  • Prevent ice dams: Heavy snow can result in ice dams that can lead to water damage and mold growth indoors.
    • Air seal between the house and attic, to prevent warm air from entering the attic and melting any snow that accumulates on the roof.
    • Air seal and insulate ductwork in the attic.

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Heat wave

  • Keep air-conditioned air out of the attic*: Air seal ductwork and air handlers in attic (*Note that there are a few homes where the attic is intentionally air conditioned, and this would not apply.)
  • Reduce unwanted solar heating of your home, in other words, reduce solar gains.
    • Add reflective coating on the roof.
    • Add reflective film on windows.
    • When you reroof choose a light color.
    • When you get new windows, select windows with low solar heat gain.

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Extreme Heat and Indoor Air Quality

Resources on IAQ and Changing Outdoor Environmental Conditions 

Indoor Air Quality (IAQ)

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Last updated on August 5, 2025