FAQ's

Terms/Definitions

 

Questions/Answers

 

Crawlspaces

 

Crawlspaces are not part of the breathing environment, and are generally not intended to be as clean as the living area of the home or building.  Crawlspaces are often in communication with outside air (through vents), so ambient conditions in a crawlspace will tend to approximate outdoor conditions.  For these reasons, it is important to ensure that crawlspace air cannot travel into the living area of the home or building.  All plumbing insertions, ductwork, or other penetrations should be properly sealed to eliminate air movement between the crawlspace and the breathing environment.

 

Vapor barriers should be installed in the crawlspace to minimize the introduction of soil moisture into the crawlspace air.  These vapor barriers should be constructed of 6-mil polyethylene.  All soil should be covered and all joints should be taped or otherwise sealed.  By extending the vapor barriers up the foundation walls and over the crawlspace vents, soil moisture is allowed to escape and the crawlspace itself is kept dry.

 

Since the crawlspace is in contact with outside air (and is generally a few degrees cooler), condensation is often a problem.  All HVAC ductwork should be insulated to eliminate exposed metal.  Floors should be insulated (even in warmer climates, where the floor insulation actually prevents condensation on floor surfaces cooled by HVAC systems) with fiberglass insulation.

 

Exhaust Fans

 

All bathrooms should be equipped with exhaust fans to eliminate the excess moisture created by showering, bathing, or other bathroom activities.  These exhaust fans (along with kitchen or dryer exhaust fans) should always discharge to the outside, rather than to the attic or crawlspace.

 

If bathroom exhaust fans cannot be installed, other means of humidity reduction (dehumidifiers, etc.) should be employed to minimize excess moisture and prevent mold growth.

 

Grading and Drainage

 

Site grading and drainage plays a huge role in indoor air quality.  If surface water is directed towards or trapped against the foundation wall, moisture may enter the basement or crawlspace.  This moisture will raise the relative humidity of the home, encouraging mold growth.  To keep surface water from entering the home, the homeowner or building manager should take a number of actions.  These include the installation of gutters (provided they are well-maintained and that the downspouts discharge at least six feet from the foundation wall), re-grading the soil near the foundation to ensure the proper slope to direct water away, and eliminating swales or gullies that carry water towards the home.  Accumulations of mulch or organic debris against the foundation walls or on the roof (pine needles, leaves, etc.) that might trap and hold moisture should also be eliminated.

 

 

Heating, Ventilation, and Air Conditioning (HVAC) System

 

Proper operation of the HVAC system is the backbone of any indoor air quality plan.  The HVAC system should be regularly inspected by qualified personnel to ensure proper operation.  In addition, regular examination of the ductwork is necessary to identify and repair all leaks, damage, or other problems.

 

The thermostat inside the home should be set to the proper room temperature (~72°F) to ensure both regular system cycling (which provides dehumidification) and also to prevent abnormally cool surfaces that might encourage condensation.  In addition, the fan should always be set to the “AUTO” position.  Setting the fan to “ON” will cause the fan to continue running even when the thermostat set point temperature has been satisfied.  Areas of negative building pressure will develop, causing humid outdoor air to enter the home at an increased rate.  This air will be circulated throughout the home by the HVAC system (which no longer dehumidifies the air when the compressor is not operating). Over time, the indoor relative humidity will increase and mold growth will begin.

 

Microbial growth (including bacteria, mold, and algae) often occurs in the condensate drain pan, since this area receives a constant supply of moisture during the cooling season.  This microbial growth can clog the drain line, resulting in an overflow that can damage underlying building materials.  The drain pan should be regularly inspected to prevent this microbial growth.  The regular addition of chlorine bleach or an algicide tablet will discourage microbial growth and prevent clogging.  The discharge point of the condensate drain line should be located outside the home or building, at a minimum of six feet away from the foundation wall.

 

Lead Base Paint (LBP)

 

Lead poisoning, the No. 1 environmental illness of children, is caused primarily by lead-based paint in older homes. The most common exposure to lead by children is through the ingestion of paint chips and contaminated dust from deteriorated or disturbed lead-based paint in homes built before 1978.

 

Lead-based paint was used both inside and outside of homes, especially on windows, baseboards, trim and doors to ensure its durability. After many years of exposure to moisture and climate changes, the paint begins to deteriorate, causing lead dust and chips to settle in window wells, and on door frames and porches. Even the deepest layers of lead-based paint can be disturbed during remodeling or home repair. The only way to know for sure if your home contains lead-based paint is to have it tested by a licensed lead professional. 

 

 

Mold Growth

 

Mold growth is one of the leading causes of indoor air quality problems.  Mold spores are potential allergens, meaning that they can trigger allergic responses much like animal dander or pollen.  In addition, some types of mold produce toxins that can be harmful to humans.  All visible mold growth should be removed from the indoor environment as quickly as possible.  Mold sampling should only be performed to determine a specific hypothesis.  If mold growth is already visible, sampling is often a waste of time and money, as all mold growth is cleaned in the same manner.

 

Light mold growth may be cleaned by the homeowner or building manager (while using the proper personal protective equipment, including eye protection, gloves, and dust masks).  Cleaning methods should include an antifungal detergent and light abrasion to remove all fungal growth.  If the area of mold growth is greater than ten square feet, a professional mold contractor should be consulted.  Smaller areas of heavy mold growth (especially growth that warrants drywall removal) should also be handled by a professional.

 

 

Negative Building Pressure

 

Negative building pressure results when an HVAC system inside a building draws in more air from the return ducts than it expels through the supply ducts.  A building can be wholly under negative pressure, or exhibit zones of negative pressure in certain areas (e.g. a room contains a return air grille and no supply grille).  Given the current configuration of most HVAC systems, most buildings operate under some degree of negative pressure.

When buildings operate under negative pressure, some air must be introduced from outside to balance the pressure differential.  Ideally, this air would enter the HVAC unit through a valve or duct and be dehumidified before being introduced to the indoor environment.  Unfortunately, however, this is rarely the case.  HVAC units often have no allowance for outside air, meaning the air must be brought in from different areas.  This often results in air being sucked in around doors and windows, through cracks in the foundation, or through other penetrations in the building skin.  When this occurs, the introduced air is not dehumidified before entering the indoor environment.  Over time, the indoor relative humidity will increase, potentially causing mold growth on cool interior surfaces or inside wall cavities.  In addition, negative building pressure can introduce soil gases into the home, including radon.

 

To eliminate negative building pressure, the HVAC system must be reconfigured so that any outside air that comes into the home passes over the condenser coils.  This can be accomplished by adding an outside air allowance valve to the air handler unit.  This process requires careful calculation and precision, so it should only be attempted by a professional.

 

Radon

 

Radon is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product ofuranium.  Radon gas from natural sources can accumulate in buildings, especially in confined areas such as attics, and basements.

 

Epidemiological evidence shows a clear link between breathing high concentrations of radon and incidence oflung cancer. Thus, radon is considered a significant contaminant that affects indoor air quality worldwide. According to the United States Environmental Protection Agency, radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the United States.

 

Radon has been classified by International Agency for Research on Cancer as being carcinogenic to humans.

 

 

Relative Humidity

 

The amount of water that can dissolve in a given volume of air is dependent on the temperature.  Absolutely dry air has a relative humidity of 0%; completely saturated air has a relative humidity of 100%.  When a constant volume of air and dissolved water is cooled, the relative humidity goes up.  When the temperature has dropped to a point where the relative humidity is 100%, water will condense to a liquid in the air itself or onto surfaces with a temperature below the dew point (defined as the temperature at which a given volume of air reaches 100% relative humidity).  Ideally, the relative humidity indoors should be between 35 and 55%.  Values greater than this will encourage condensation on cooler surfaces (un-insulated floors, HVAC registers, windows, etc.) and subsequent mold growth.