What is Radon Mitigation?

You have tested your home for radon, but now what? This information is for people who have tested their home for radon and confirmed that they have elevated radon levels — 4 pCi/L or higher.

The following steps can help you reduce radon in your home:

  • Select a qualified radon mitigation contractor to reduce the radon levels in your home.
  • Determine an appropriate radon reduction method.
  • Maintain your radon reduction system.

Radon reduction systems work.

Some radon reduction systems can reduce radon levels in your home by up to 99 percent. Most homes can be fixed for about the same cost as other common home repairs. Your costs may vary depending on the size and design of your home and which radon reduction methods are needed. Hundreds of thousands of people have reduced radon levels in their homes.

The New York State Department of Health and U.S. Environmental Protection Agency recommend that you have a qualified radon mitigation contractor fix your home because lowering high radon levels requires specific technical knowledge and special skills. Without the proper equipment or technical knowledge, you could actually increase your radon level or create other potential hazards and additional costs. However, if you decide to do the work yourself, get information on appropriate training courses and technical guidance documents from the New York State Department of Health Radon Program.

Select a qualified radon mitigation contractor.

Choose a contractor to fix a radon problem just as you would choose someone to do other home repairs. It is wise to get more than one estimate, to ask for references, and to contact some of those references to ask if they are satisfied with the contractors' work.

New York State Department of Health does not regulate radon services. Ask the contractor if they hold a professional proficiency or certification credential, and if they follow industry consensus standards such as the American Society for Testing and Materials, ASTM, Standard Practice for Installing Radon Mitigation Systems in Existing Low-Rise Residential Buildings, E2121.

  • Evaluate and Compare Contractors

    Ask the following questions and then use this checklist when evaluating and comparing contractors:

    YES NO Question
        Will the contractor provide references or photographs, as well as test results of before and after radon levels of past radon reduction work?
        Can the contractor explain what the work will involve, how long it will take to complete, and exactly how the radon reduction system will work?
        Does the contractor charge a fee for any diagnostic tests? Although many contractors give free estimates, they may charge for diagnostic tests. These tests help determine what type of radon reduction system should be used and in some cases are necessary, especially if the contractor is unfamiliar with the type of home structure or the anticipated degree of difficulty. See "Radon Reduction Techniques" for more on diagnostic tests.
        Did the contractor inspect your home's structure before giving you an estimate?
        Did the contractor review the quality of your radon measurement results and determine if appropriate testing procedures were followed?
  • Compare Contractors' Costs

    Compare the contractors' proposed costs and consider what you will get for your money, taking into account: a less expensive system may cost more to operate and maintain; a less expensive system may have less aesthetic appeal; a more expensive system may be best for your home; and, the quality of the building material will affect how long the system lasts.

    YES NO Does the contractor's proposal and estimate include?
        Proof of professional proficiency or certification credentials?
        Proof of liability insurance and being bonded, and having all necessary licenses to satisfy local requirements?
        Diagnostic testing prior to design and installation of a radon reduction system?
        Installation of a warning device to caution you if the radon reduction system is not working correctly?
        Testing after installation to make sure the radon reduction system works well? (The New York State Department of Health Radon Program will provide a free radon test kit within one year of a radon mitigation system being installed in your home.)
        A guarantee to reduce radon levels to 4 pCi/L or below. And if so, for how long?
  • The Contract

    Ask the contractor to prepare a contract before any work starts. Carefully read the contract before you sign it. Make sure everything in the contract matches the original proposal. The contract should describe exactly what work will be done prior to and during the installation of the system, what the system consists of, and how the system will operate. Many contractors provide a guarantee that they will adjust or modify the system to reach a negotiated radon level. Carefully read the conditions of the contract describing the guarantee. Carefully consider optional additions to your contract which may add to the initial cost of the system, but may be worth the extra expense. Typical options might include an extended warranty, a service plan and/or improved aesthetics.

    Verified Does the Contract Include?
      The total cost of the job, including all taxes and permit fees; how much, if any, is required for a deposit; and when payment is due in full.
      The time needed to complete the work.
      An agreement by the contractor to obtain necessary permits and follow required building codes.
      A statement that the contractor carries liability insurance and is bonded and insured to protect you in case of injury to persons, or damage to property, while the work is done.
      A guarantee that the contractor will be responsible for damage and cleanup after the job.
      Details of any guarantee to reduce radon below a negotiated level.
      Details of warranties or other optional features associated with the hardware components of the mitigation system.
      A declaration stating whether any warranties or guarantees are transferable if you sell your home.
      A description of what the contractor expects the homeowner to do, such as make the work area accessible, before work begins.

Types of Radon Mitigation

In homes that have a basement or a slab-on-grade foundation, radon is usually reduced by one of four types of soil suction:

  • subslab suction
  • drain-tile suction
  • sump-hole suction
  • block-wall suction
  • Subslab Suction

    • Active Subslab Suction

      Active subslap suction — also called subslab depressurization — is the most common and usually the most reliable radon reduction method. One or more suction pipes are inserted through the floor slab into the crushed rock or soil underneath. They also may be inserted below the concrete slab from outside the home. The number and location of suction pipes that are needed depends on how easily air can move in the crushed rock or soil under the slab and on the strength of the radon source. Often, only a single suction point is needed.

      A contractor usually gets this information from visual inspection, from diagnostic tests, and/or from experience. A radon vent fan connected to the suction pipes draws the radon gas from below the home and releases it into the outdoor air while simultaneously creating a negative pressure or vacuum beneath the slab. Common fan locations include unconditioned home and garage spaces, including attics, and the exterior of the home.

    • Passive Subslab Suction

      Passive subslab suction is the same as active subslab suction except it relies on natural pressure differentials and air currents instead of a fan to draw radon up from below the home. Passive subslab suction is usually associated with radon-resistant features installed in newly constructed homes. Passive subslab suction is generally not as effective in reducing high radon levels as active subslab suction.

  • Drain-Tile Suction

    Some homes have drain tiles or perforated pipe to direct water away from the foundation of the home. Suction on these tiles or pipes is often effective in reducing radon levels.

  • Sump-Hole Suction

    One variation of subslab and drain tile suction is sump-hole suction. Often, when a home with a basement has a sump pump to remove unwanted water, the sump can be capped so that it can continue to drain water and serve as the location for a radon suction pipe.

  • Block-Wall Suction

    Block-wall suction can be used in basement homes with hollow block foundation walls. This method removes radon and depressurizes the block wall, similar to subslab suction. This method is often used in combination with subslab suction.

  • Crawlspace Ventilation

    In some cases, radon levels can be lowered by ventilating the crawlspace passively, or actively, with the use of a fan. Crawlspace ventilation may lower indoor radon levels both by reducing the home's suction on the soil and by diluting the radon beneath the home. Passive ventilation in a crawlspace is achieved by opening vents, or installing additional vents. Active ventilation uses a fan to blow air through the crawlspace instead of relying on natural air circulation. In colder climates, for either passive or active crawlspace ventilation, water pipes, sewer lines and appliances in the crawlspace may need to be insulated against the cold. These ventilation options could result in increased energy costs for the home.

    An effective method to reduce radon levels in crawlspace homes involves covering the earth floor with a high-density plastic sheet. A vent pipe and fan are used to draw the radon from under the sheet and vent it to the outdoors. This form of soil suction is called submembrane suction, and when properly applied is the most effective way to reduce radon levels in crawlspace homes. Another less-favorable option is active crawlspace depressurization which involves drawing air directly from the crawlspace using a fan. This technique generally does not work as well as submembrane suction and requires special attention to combustion appliance backdrafting and sealing the crawlspace from other portions of the home, and may also result in increased energy costs due to loss of conditioned air from the home.

Additional Radon Reduction Techniques

Other radon reduction techniques that can be used in any type of home include:

  • sealing
  • home or room pressurization
  • heat recovery ventilation
  • natural ventilation
  • Sealing

    Sealing cracks and other openings in the foundation is a basic part of most approaches to radon reduction. Sealing the cracks limits the flow of radon into your home, thereby making other radon reduction techniques more effective and cost-efficient. It also reduces the loss of conditioned air. EPA does not recommend the use of sealing alone to reduce radon because, by itself, sealing has not been shown to lower radon levels significantly or consistently. It is difficult to identify and permanently seal the places where radon is entering. Normal settling of your home opens new entry routes and reopens old ones.

  • Home or Room Pressurization

    Home or room pressurization uses a fan to blow air into the basement, or living area from either upstairs or outdoors. It attempts to create enough pressure at the lowest level indoors — in a basement, for example — to prevent radon from entering into the home. The effectiveness of this technique is limited by home construction, climate, other appliances in the home and occupant lifestyle. In order to maintain enough pressure to keep radon out, the doors and windows at the lowest level must not be left open, except for normal entry and exit. This approach generally results in more outdoor air being introduced into the home, which can cause moisture intrusion and energy penalties. Consequently, this technique should only be considered after the other, more-common techniques have not sufficiently reduced radon.

  • Heat Recovery Ventilation

    A heat recovery ventilator, or HRV, also called an air-to-air heat exchanger, can be installed to increase ventilation which will help reduce the radon levels in your home. An HRV will increase ventilation by introducing outdoor air while using the heated or cooled air being exhausted to warm or cool the incoming air. HRVs can be designed to ventilate all or part of your home, although they are more effective in reducing radon levels when used to ventilate only the basement. If properly balanced and maintained, they ensure a constant degree of ventilation throughout the year. HRVs also can improve air quality in homes that have other indoor pollutants. There could be significant increase in the heating and cooling costs with an HRV, but not as great as ventilation without heat recovery.

  • Natural Ventilation

    Some natural ventilation occurs in all homes. By opening windows, doors, and vents on the lower floors you increase the ventilation in your home. This increase in ventilation mixes outdoor air with the indoor air containing radon, and can result in reduced radon levels. However, once windows, doors and vents are closed, radon concentrations most often return to previous values within about 12 hours. Natural ventilation in any type of home should normally be regarded as only a temporary radon reduction approach because of the following disadvantages: loss of conditioned air and related discomfort; greatly increased costs of conditioning additional outside air; and security concerns.

Radon in Water

Radon in water is usually not the primary source of radon in the home. If a radon in air mitigation system appears not to be reducing radon levels, then radon in water may be evaluated as a pathway. Presently there is no guideline or recommended action level for radon in water concentration. Radon in water may pose an inhalation risk. This risk results when radon is released into the air when water is used for showering and other household purposes. Approaches to mitigate radon in water are aeration or filtration using granular activated carbon.

Checking Your Contractor's Work

Below is a list of basic installation requirements that your contractor should meet when installing a radon reduction system in your home. It is important to verify with your contractor that the radon mitigation standards (ASTM E2121 in particular) are properly met to ensure that your radon reduction system will be effective. You can also check with your state radon office to see if there are state requirements that your contractor must meet.

Verified Basic Installation Requirements
  Radon reduction systems must be clearly labeled. This will avoid accidental changes to the system that could disrupt its function.
  The exhaust pipes of soil suction systems must vent above the surface of the roof and 10 feet or more above the ground, and must be at least 10 feet away from windows, doors, or other openings that could allow the radon to reenter the home, if the exhaust pipes do not vent at least 2 feet above these openings.
  The exhaust fan must not be located in or below a livable area. For instance, it should be installed in unconditioned space.
  If installing an exhaust fan outside, the contractor must install a fan that meets local building codes for exterior use.
  Electrical connections of all active radon reduction systems must be installed according to local electrical codes.
  A warning device must be installed to alert you if an active system stops working properly. Examples of system failure warning devices are: a liquid gauge, a sound alarm, a light indicator, and a dial, or needle display, gauge. The warning device must be placed where it can be seen or heard easily. Your contractor should check that the warning device works. Later on, if your monitor shows that the system is not working properly, call a contractor to have it checked.
  A post-mitigation radon test should be done within 30 days of system installation, but no sooner than 24 hours after your system is in operation with the fan on, if it has one. The contractor may perform a post-mitigation test to check his work and the initial effectiveness of the system; however, it is recommended that you also get an independent follow-up radon measurement. Having an independent tester perform the test, or conducting the measurement yourself, will eliminate any potential conflict of interest. To test the system's effectiveness, a two- to seven-day measurement is recommended. Test conditions: windows and doors must be closed 12 hours before and during the test, except for normal entry and exit.
  Make sure your contractor completely explains your radon reduction system, demonstrates how it operates and explains how to maintain it. Ask for written operating and maintenance instructions and copies of any warranties.

Installation and Operating Costs

Technique Typical Radon Reduction Comments
Subslab Suction (Subslab Depressurization) 50 to 99 percent Works best if air can move easily in material under slab.
Passive Subslab Suction 30 to 70 percent May be more effective in cold climates; not as effective as active subslab suction. Usually installed in new construction situations.
Drain Tile Suction 50 to 99 percent Can work with either partial or complete drain tile loops.
Block-Wall Suction 50 to 99 percent Only in homes with hollow block-walls; requires sealing of major openings.
Sump-Hole Suction 50 to 99 percent Works best if air moves easily to sump from under the slab.
Submembrane Depressurization in a Crawlspace 50 to 99 percent Less heat loss than natural ventilation in cold winter climates.
Natural Ventilation in a Crawlspace 0 to 50 percent Costs variable
Sealing of Radon Entry Routes See Comments Normally only used with other techniques; proper materials and installation required
Home (Basement) Pressurization 50 to 99 percent Works best with tight basement isolated from outdoors and upper floors.
Natural Ventilation Variable/ Temporary Significant heated or cooled air loss; operating costs depend on utility rates and amount of ventilation.
Heat Recovery Ventilation, or HRV Variable/ See Comments Limited use; effectiveness limited by radon concentration and the amount of ventilation air available for dilution by the HRV. Best applied to limited-space areas like basements.
Private Well Water Systems: Aeration 95 to 99 percent Generally more efficient than GAC; requires annual cleaning to maintain effectiveness and to prevent contamination; requires venting radon to outdoors.
Private Well Water Systems: Granular Activated Carbon, or GAC 85 to 99 percent Less efficient for higher levels than aeration; use for moderate levels, around 5,000 pCi/L or less in water; radioactive radon by-products can build on carbon; may need radiation shield around tank and care in disposal.
NOTE: Mitigation costs vary due to technique, materials and the extent of the problem. Typically the cost of radon mitigations are comparable to other common home repairs.