Damp environments, poorly maintained heating and air-conditioning systems and carpeting may contribute to poor indoor air quality, according to experts at the annual meeting of the American College of Allergy, Asthma and Immunology (ACAAI) in Miami Beach, Fla. Americans spend about 90 percent of their time indoors, where they are repeatedly exposed to indoor allergens and airborne particles that can lead to respiratory symptoms and conditions.
"If there was just one thing I could do to fix buildings, it would be to change the relative humidity," said Doug Garrett, CEM, CDSM, building scientist and president of Building Performance and Comfort, Leander, Texas. "Moisture leads to conditions that are conducive to dust mites and mold, as well as bacteria, yeast and other living organisms."
Garrett pointed to dust mites and mold as particularly worrisome.
A damp building with high humidity may lead to increased levels of dust mites and mold, leading to increased allergic respiratory symptoms, as well as the worsening of asthma. And even if someone is not allergic, molds may produce mycotoxins and volatile organic chemicals (VOCs) that smell bad and may cause respiratory irritation, he said.
Dust mites are microscopic arachnids that thrive in humidity. They cause allergic reactions and trigger asthma symptoms. Nearly half of all young people with asthma are allergic to dust mites; about 10 percent of the population is allergic to dust mites.
Mold requires moisture to grow. Indoor environments house many sources of moisture including condensation and leaky pipes.
Indoor Breathing Environment
Although there are many culprits that negatively affect indoor air quality, poorly maintained air-conditioning and carpeting are among the most problematic.
"A home's heating and air-conditioning (HVAC) system, if poorly maintained, can become a major source of microbial allergens," said Garrett.
According to Garrett, up to 30 percent of the air inside a home can come from the attic, parking garage or basement. One study supported by the EPA found that 75 percent of homes had carbon monoxide from the garage inside of the home.
Like air conditioning systems, carpeting often harbors allergens, including dust mites and molds said Jeffrey May, M.A., principal scientist of May Indoor Air Investigations LLC, Tyngsborough, Mass. Organisms and particles that become airborne eventually settle in carpeting. In damp environments, carpeting provides an ideal environment for mold growth.
"Many schools shampoo their carpeting right before school starts at the end of summer when it's humid outside," said May. "There couldn't be a worse time."
Making a Healthier Indoor Environment
To improve indoor air quality, Garrett lists several construction practices that, when done right, can make a significant difference. These include installing tight ductwork, achieving airtight construction, using a correctly sized HVAC (heating, ventilation and air conditioning) system and making sure there is fresh air ventilation. Proper ventilation involves introducing air from a known source and then filtering, dehumidifying and pre-cooling or heating it.
"You can't build houses too airtight," said Garrett. "But you can under ventilate them."
Once built, maintenance becomes key. May offers the following advice for home owners on making their indoor environments healthier:
•Keep the air conditioner clean. Use a filter with an American Society of Heating and Air-Conditioning Engineers (AHRAE) Standard MERV (Minimum Efficiency Reporting Value) of at least 8.
•Do not have carpeting in any buildings or homes where humidity can't be controlled. If you cannot replace carpet, vacuum thoroughly, carefully and methodically so you don't stir dust into the air. Use a vacuum with a HEPA filter or cyclonic vacuum.
•Prevent mold by dehumidifying the basement. In unfinished basements, humidity should be kept lower than 50 percent. Do research before buying a dehumidifier. "There are scams out there" said May. "And 'exhaust only' systems are not effective."