Building Your Home

Radon Information & Indoor Problems

Colorado is a Red State - Build Your Home to be Radon Resistant!

What is Radon?

Radon is a gas that has no color, odor, or taste and comes from the natural radioactive breakdown of uranium in the ground.  You can be exposed to radon by two main sources: (1) radon in the air in your home (frequently called "radon in indoor air") and (2) radon in drinking water.  Radon can get into the air your breathe and into the water you drink.  Radon is also found in small amounts in outdoor air.

Radon is a gaseous radioactive element having the symbol Rn, the atomic number 86, an atomic weight of 222, a melting point of -71° C, a boiling point of -62° C, and (depending on the source, there are between 20 and 25 isotopes of radon - 20 cited in the chemical summary, 25 listed in the table of isotopes); it is an extremely toxic, colorless gas; it can be condensed to a transparent liquid and to an opaque, glowing solid; it is derived from the radioactive decay of radium and is used in cancer treatment, as a tracer in leak detection, and in radiography.

Most of the radon in indoor air comes from soil underneath the home. As uranium breaks down, radon gas forms and seeps into the house.  Radon from soil can get into any type of building - homes, offices, and schools - and build up to high levels in the air inside the building.

About The Map

The purpose of this map is to assist National, State, and local organizations to target their resources and to implement radon-resistant building codes.  This map is not intended to be used to determine if a home in a given zone should be tested for radon.  Homes with elevated levels of radon have been found in all three zones.  All homes should be tested regardless of geographic location.  Important points to note:

  • All homes should test for radon, regardless of geographic location or zone designation.
  • There are many thousands of individual homes with elevated radon levels in Zone 2 and 3.  Elevated levels can be found in Zone 2 and Zone 3 counties.
  • EPA also recommends that this map be supplemented with any available local data in order to further understand and predict the radon potential of a specific area.  For more information, contact your state radon coordinator to see if your state has more detailed information available.
  • The map should not be used in lieu of testing during real estate transactions.

The Map was developed using five factors to determine radon potential: indoor radon measurements; geology; aerial radioactivity; soil permeability; and, foundation type.  Radon potential assessment is based on geologic provinces.  Radon Index Matrix is the quantitative assessment of radon potential.  Confidence Index Matrix shows the quantity and quality of the data used to assess radon potential.  Geologic Provinces were adapted to county boundaries for the Map of Radon Zones.

Radon gas can also dissolve and accumulate in water from underground sources (called ground water), such as wells.  When water that contains radon is used in the home for showering, washing dishes, and cooking, radon gas escapes from the water and goes into the air.  It is similar to carbonated soda drinks where carbon dioxide is dissolved in the soda and is released when you open the bottle.  Some radon also stays in the water.  Radon is not a concern in water that comes from lakes, rivers, and reservoirs (called surface water), because the radon is released into the air before it ever arrives at your tap.

Why is Radon the Public Health Risk that it is?

EPA estimates that about 20,000 lung cancer deaths each year in the U.S. are radon related.  Exposure to radon is the second leading cause of lung cancer after smoking.  Radon is an odorless, tasteless and invisible gas produced by the decay of naturally occurring uranium in soil and water.  Radon is a form of ionizing radiation and a proven carcinogen.  Lung cancer is the only known effect on human health from exposure to radon in air.  Thus far, there is no evidence that children are at greater risk of lung cancer than are adults.

Radon & Lung Cancer Studies Find Direct Evidence Linking Radon in Homes to Lung Cancer - Two studies show definitive evidence of an association between residential radon exposure and lung cancer.  Two studies, a North American study and a European study, both combined data from several previous residential studies.  These two studies go a step beyond earlier findings.  They confirm the radon health risks predicted by occupational studies of underground miner’s who breathed radon for a period of years.  Early in the debate about radon related risks, some researchers questioned whether occupational studies could be used to calculate risks from exposure to radon in the home environment.  “These findings effectively end any doubts about the risks to Americans of having radon in their homes,” said Tom Kelly, Director of EPA’s Indoor Environments Division.  “We know that radon is a carcinogen.  This research confirms that breathing low levels of radon can lead to lung cancer.”

Is There Radon in My Water?

Not all drinking water contains radon.  If your drinking water comes from a surface water source, such as a river, lake, or reservoir, most radon that might be in the water will be released into the air before reaching your water supplier or home.  Radon is only a concern if your drinking water comes from underground, such as a well that pumps water from an aquifer, though not all water from underground sources contains radon.

If you get your water from a public water system that serves 25 or more year-around residents, you will receive an annual water quality report.  A major public right-to-know initiative of the 1996 Amendments to the Safe Drinking Act.

Builders & Contractors
How Radon Enters a House

Basic Techniques for Radon-Resistant New Construction.  All of the techniques and materials described below are commonly used in home construction.  No special skills or materials are required when adding radon-resistant features as a new home is being built.  While the techniques may vary for different house foundations and building site requirements, the five basic features that builders should include to prevent radon from entering a home are:

Gravel - Use a 4-inch layer of clean, coarse gravel below the “slab,” also called the foundation.  This layer of gravel allows the soil gases – including radon – that occur naturally in the soil to move freely underneath the house.  Builders call this the “air flow layer” or “gas permeable layer” because the loose gravel allows the gases to circulate.  NOTE:  In some regions of the country, gravel may be too expensive or unnecessary.  Alternatives are allowed, such as a perforated pipe or a collection mat.  All homes should be tested for radon.

Plastic Sheeting or Vapor Retarder - Place heavy duty plastic sheeting (6 mil. polyethylene) or a vapor retarder on top of the gravel to prevent the soil gases from entering the house.  The sheeting also keeps the concrete from clogging the gravel layer when the slab is poured.

A Vent Pipe - Run a 3-inch or 4-inch solid PVC Schedule 40 pipe, like the ones commonly used for plumbing, vertically from the gravel layer (stubbed up when the slab is poured) through the house’s conditioned space and roof to safely vent radon and other soil gases outside above the house.  (Although serving a different purpose, this vent pipe is similar to the drain waste vent – DWV – installed by the plumber.)  This pipe should be labeled "Radon System."  Your plumber or a certified radon professional can do this.

Sealing and Caulking - Seal all openings, cracks, and crevices in the concrete foundation floor (including the slab perimeter crack) and walls with polyurethane caulk to prevent radon and other soil gases from entering the home.

Junction Box - Install an electrical junction box (outlet) in the attic for use with a vent fan, should, after testing for radon, a more robust system be needed.

The cost to a builder of including radon-resistant features in a new home during construction can vary widely.  Many builders routinely include these features in some of their homes.  The cost to the builder of including these features is typically less than the cost to mitigate the home after construction.  Builders should provide customers with a checklist of included features.  New home buyers may ask the builder about these features, and if not provided, may ask the builder to include them in the new home.  If a home is tested after buyers move in and an elevated level of radon is discovered, the owners’ cost of fixing the problem can be much more.

Financing Residential Radon Mitigation Costs:  Using the HUD 203(k) Mortgage
Insurance Program to Reduce the Risk of Lung Cancer in People

The Section 203(k) mortgage financing program is the Housing and Urban Development's (HUD) primary tool for rehabilitating and improving single family homes.  The program allows home buyers to finance the purchase and repair or improvement of a home using a single mortgage loan.  Reducing radon levels in a home is an improvement that can be financed through a 203(k) mortgage loan.

Part of the 203(k) mortgage proceeds must be used to pay the costs of rehabilitating or improving a residential property.  To qualify, the total cost of the eligible repairs or improvements, including fixes to reduce radon levels, must be at least $5,000.  The 203(k) program is an important tool for expanding home ownership, revitalizing homes, neighborhoods and communities, and for making homes healthier and safer for those who occupy them.

Homes eligible for 203(k) financing include:
  • one to four-family dwellings that have been completed for at least one year;
  • dwellings that have been demolished, provided some of the existing foundation system remains;
  • converting a one-family dwelling into a two, three, or four-family dwelling; or, alternatively, converting an existing multi-unit dwelling into a one to four-family unit.

The 203(k) program has been used successfully by many lenders to rehabilitate properties through partnerships with state and local housing agencies, and with non-profit organizations.  To further help borrowers buy homes, lenders have found innovative ways to combine the 203(k) program with other financial resources like HUD's HOPE and Community Development Block Grant Programs.

Contact an FHA-approved lender in your area for more information about HUD’s 203(k) program, or if you’re interested in getting a 203(k) insured mortgage loan.  Check your phone directory’s blue pages for the HUD office nearest you; they can get you a list of the 203(k) approved lenders in your area.

Indoor Air Problems

Building a new home provides the opportunity for preventing indoor air problems.  However, it can result in exposure to higher levels of indoor air contaminants if careful attention is not given to potential pollution sources and the air exchange rate.  Express your concerns about indoor air quality to your architect or builder and enlist his or her cooperation in and taking measures to provide good indoor air quality.  Talk both about purchasing building materials, and furnishings that are low-emitting and about providing an adequate amount of ventilation.

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) recommends a ventilation rate of 0.35 ach (air changes per hour) for new homes, and some new homes are built to even tighter specifications.  Particular care should be given in such homes to preventing the build-up of indoor air pollutants to high levels.

Here are a few important actions that can make a difference:

  • Use radon-resistant construction techniques.
  • Obtain a copy of the EPA booklet, Model Standards and Techniques for Control of Radon in New Residential Buildings, from your state radon office or health agency, your state homebuilders' association, or your EPA regional office.  You can also visit EPA's Radon Resistant New Construction (RRNC) site and read "Building Radon Out: A Step-by-Step Guide on How to Build Radon-Resistant Homes" EPA 402-K-01-002, April 2001
  • Choose building materials and furnishings that will keep indoor air pollution to a minimum.
  • Provide proper drainage and seal foundations in new construction.  Air that enters the home through the foundation can contain more moisture than is generated from all occupant activities.  Become familiar with mechanical ventilation systems and consider installing one.  Advanced designs of new homes are starting to feature mechanical systems that bring outdoor air into the home.  Some of these designs include energy-efficient heat recovery ventilators (also known as air-to-air heat exchangers).  Ensure that combustion appliances, including furnaces, fireplaces, woodstoves, and heaters, are properly vented and receive enough supply air.  Combustion gases, including carbon monoxide, and particles can be back-drafted from the chimney or flue into the living space if the combustion appliance is not properly vented or does not receive enough supply air.  Back-drafting can be a particular problem in weatherized or tightly constructed homes.  Installing a dedicated outdoor air supply for the combustion appliance can help prevent back drafting.

What About Carpet?

In recent years, a number of consumers have associated a variety of symptoms with the installation of new carpet.  Scientists have not been able to determine whether the chemicals emitted by new carpets are responsible.  If you are installing new carpet, you may wish to take the following steps:

  • Talk to your carpet retailer.  Ask for information on emissions from carpet.
  • Ask the retailer to unroll and air out the carpet in a well-ventilated area before installation.
  • Ask for low-emitting adhesives if adhesives are needed.
  • Consider leaving the premises during and immediately after carpet installation.  You may wish to schedule the installation when most family members or office workers are out.
  • Be sure the retailer requires the installer to follow the Carpet and Rug Institute's installation guidelines.
  • Open doors and windows.  Increasing the amount of fresh air in the home will reduce exposure to most chemicals released from carpet.  During and after installation, use window fans, room air conditioners, or other mechanical ventilation equipment you may have installed in your house, to exhaust fumes to the outdoors.  Keep them running for 48 to 72 hours after the new carpet is installed.
    • Contact your carpet retailer if objectionable odors persist.
    • Follow the manufacturer's instructions for proper carpet maintenance.


Sources:  Pressed wood products (hardwood plywood wall paneling, particleboard, fiberboard) and furniture made with these pressed wood products.  Urea-formaldehyde foam insulation (UFFI).  Combustion sources and environmental tobacco smoke.  Durable press drapes, other textiles, and glues.

Health Effects:  Eye, nose, and throat irritation; wheezing and coughing; fatigue; skin rash; severe allergic reactions.  May cause cancer.  May also cause other effects listed under "organic gases."

Levels in Homes:  Average concentrations in older homes without UFFI are generally well below 0.1 (ppm).  In homes with significant amounts of new pressed wood products, levels can be greater than 0.3 ppm.

Steps to Reduce Exposure:

  • Use "exterior-grade" pressed wood products (lower-emitting because they contain phenol resins, not urea resins).
  • Use air conditioning and dehumidifiers to maintain moderate temperature and reduce humidity levels.
  • Increase ventilation, particularly after bringing new sources of formaldehyde into the home.

Stoves, Heaters, Fireplaces, and Chimneys

In addition to environmental tobacco smoke, other sources of combustion products are unvented kerosene and gas space heaters, woodstoves, fireplaces, and gas stoves.  The major pollutants released are carbon monoxide, nitrogen dioxide, and particles.  Unvented kerosene heaters may also generate acid aerosols.

Combustion gases and particles also come from chimneys and flues that are improperly installed or maintained and cracked furnace heat exchangers.  Pollutants from fireplaces and woodstoves with no dedicated outdoor air supply can be "back-drafted" from the chimney into the living space, particularly in weatherized homes.

Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless gas that interferes with the delivery of oxygen throughout the body.  At high concentrations it can cause unconsciousness and death.  Lower concentrations can cause a range of symptoms from headaches, dizziness, weakness, nausea, confusion, and disorientation, to fatigue in healthy people and episodes of increased chest pain in people with chronic heart disease.  The symptoms of carbon monoxide poisoning are sometimes confused with the flu or food poisoning.  Fetuses, infants, elderly people, and people with anemia or with a history of heart or respiratory disease can be especially sensitive to carbon monoxide exposures.

Steps to Reduce Exposure to Carbon Monoxide

It is most important to be sure combustion equipment is maintained and properly adjusted.  Vehicular use should be carefully managed adjacent to buildings and in vocational programs.  Additional ventilation can be used as a temporary measure when high levels of CO are expected for short periods of time.

  • Keep gas appliances properly adjusted.
  • Consider purchasing a vented space heater when replacing an unvented one.
  • Use proper fuel in kerosene space heaters.
  • Install and use an exhaust fan vented to outdoors over gas stoves.
  • Open flues when fireplaces are in use.
  • Choose properly sized wood stoves that are certified to meet EPA emission standards.  Make certain that doors on all wood stoves fit tightly.
  • Have a trained professional inspect, clean, and tune-up central heating system (furnaces, flues, and chimneys) annually.  Repair any leaks promptly.
  • Do not idle the car inside garage.

Nitrogen Dioxide

Nitrogen dioxide (NO2) is a reddish-brown, irritating odor gas that irritates the mucous membranes in the eye, nose, and throat and causes shortness of breath after exposure to high concentrations.  There is evidence that high concentrations or continued exposure to low levels of nitrogen dioxide increases the risk of respiratory infection; there is also evidence from animal studies that repeated exposures to elevated nitrogen dioxide levels may lead, or contribute, to the development of lung disease such as emphysema.  People at particular risk from exposure to nitrogen dioxide include children and individuals with asthma and other respiratory diseases.

Particles, released when fuels are incompletely burned, can lodge in the lungs and irritate or damage lung tissue.  A number of pollutants, including radon and benzo(a)pyrene, both of which can cause cancer, attach to small particles that are inhaled and then carried deep into the lung.

Reducing Exposure to Combustion Products in Homes

Take special precautions when operating fuel-burning unvented space heaters.

Consider potential effects of indoor air pollution if you use an unvented kerosene or gas space heater.  Follow the manufacturer's directions, especially instructions on the proper fuel and keeping the heater properly adjusted.  A persistent yellow-tipped flame is generally an indicator of maladjustment and increased pollutant emissions.  While a space heater is in use, open a door from the room where the heater is located to the rest of the house and open a window slightly.

Install and use exhaust fans over gas cooking stoves and ranges and keep the burners properly adjusted.

Using a stove hood with a fan vented to the outdoors greatly reduces exposure to pollutants during cooking.  Improper adjustment, often indicated by a persistent yellow-tipped flame, causes increased pollutant emissions.  Ask your gas company to adjust the burner so that the flame tip is blue.  If you purchase a new gas stove or range, consider buying one with pilotless ignition because it does not have a pilot light that burns continuously.  Never use a gas stove to heat your home.  Always make certain the flue in your gas fireplace is open when the fireplace is in use.

Keep woodstove emissions to a minimum.  Choose properly sized new stoves that are certified as meeting EPA emission standards.

Make certain that doors in old woodstoves are tight-fitting.  Use aged or cured (dried) wood only and follow the manufacturer's directions for starting, stoking, and putting out the fire in woodstoves.  Chemicals are used to pressure-treat wood; such wood should never be burned indoors.  Because some old gaskets in woodstove doors contain asbestos, when replacing gaskets refer to the instructions in the CPSC, ALA, and EPA booklet, Asbestos in Your Home, to avoid creating an asbestos problem. New gaskets are made of fiberglass.)

Have central air handling systems, including furnaces, flues, and chimneys, inspected annually and promptly repair cracks or damaged parts.

Blocked, leaking, or damaged chimneys or flues release harmful combustion gases and particles and even fatal concentrations of carbon monoxide.  Strictly follow all service and maintenance procedures recommended by the manufacturer, including those that tell you how frequently to change the filter.  If manufacturer's instructions are not readily available, change filters once every month or two during periods of use.  Proper maintenance is important even for new furnaces because they can also corrode and leak combustion gases, including carbon monoxide.

  • Read the booklet What You Should Know About Combustion Appliances and Indoor Air Pollution to learn more about combustion pollutants.

Environmental Tobacco Smoke (ETS)

Source:  Cigarette, pipe, and cigar smoking.

Health Effects:  Eye, nose, and throat irritation; headaches; lung cancer; may contribute to heart disease.  Specifically for children, increased risk of lower respiratory tract infections, such as bronchitis and pneumonia, and ear infections; build-up of fluid in the middle ear; increased severity and frequency of asthma episodes; decreased lung function.

Levels in Homes:  Particle levels in homes without smokers or other strong particle sources are the same as, or lower than, those outdoors.  Homes with one or more smokers may have particle levels several times higher than outdoor levels.

Steps to Reduce Exposure:

  • Do not smoke in your home or permit others to do so.
  • Do not smoke if children are present, particularly infants and toddlers.
  • If smoking indoors cannot be avoided, increase ventilation in the area where smoking takes place. Open windows or use exhaust fans.


Sources:  Wet or moist walls, ceilings, carpets, and furniture; poorly maintained humidifiers, dehumidifiers, and air conditioners; bedding; household pets.

Health Effects:  Eye, nose, and throat irritation; shortness of breath; dizziness; lethargy; fever; digestive problems.  Can cause asthma; humidifier fever; influenza and other infectious diseases.

Levels in Homes:  Indoor levels of pollen and fungi are lower than outdoor levels (except where indoor sources of fungi are present).  Indoor levels of dust mites are higher than outdoor levels.

Steps to Reduce Exposure:

  • Install and use fans vented to outdoors in kitchens and bathrooms.
  • Vent clothes dryers to outdoors.
  • Clean cool mist and ultrasonic humidifiers in accordance with manufacturer's instructions and refill with clean water daily.
  • Empty water trays in air conditioners, dehumidifiers, and refrigerators frequently.
  • Clean and dry or remove water-damaged carpets.
  • Use basements as living areas only if they are leak-proof and have adequate ventilation.  Use dehumidifiers, if necessary, to maintain humidity between 30-50 percent.

Additional Resources
To report a dangerous product or a product-related injury, call the Consumer Product Safety Commission's (CPSC) hotline at (800) 638-2772 or CPSC teletypewriter at (800) 638-8270.  Consumer can obtain recall information at CPSC's web site
Consumers can report product hazards to
Centers for Disease Control and Prevention (CDC)
National Center for Environmental Health
Carbon Monoxide Poisoning Fact Sheet - (offered in many languages) -
U.S. Consumer Product Safety Commission (CPSC)
Office of Information and Public Affairs

   Online Edition