Home inspector radon reduction and radon-resistant features study guide

The Citizen's Guide says lowering high radon levels requires technical knowledge and special skills, and that you should use a contractor who is trained to fix radon problems.

“Lowering high radon levels requires technical knowledge and special skills. You should use a contractor who is trained to fix radon problems.”

EPA: A Citizen's Guide to Radon (EPA 402/K-12/002, 2025 edition)

The Consumer's Guide warns that without the proper equipment or technical knowledge you could actually increase your radon level. If you decide to do the work yourself, it says to get information on appropriate training courses from your state radon office.

“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 from your state radon office.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

To check a contractor's qualifications, the guide says to check first with your state radon office. Many states require radon professionals to be licensed, certified or registered, and to install systems that meet state requirements.

“First, check with your state radon office. Many states require radon professionals to be licensed, certified or registered, and to install radon mitigation systems that meet state requirements.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

In states that don't regulate radon services, the guide says to ask the contractor whether they hold a professional proficiency or certification credential and whether they follow industry consensus standards, such as ASTM's Standard Practice for Installing Radon Mitigation Systems in Existing Low-Rise Residential Buildings, E2121.

“In states that don't 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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

The Home Buyer's and Seller's Guide says any mitigation measures taken or system installed in your home must conform to your state's regulations. In states without regulations covering mitigation, EPA recommends that the system conform to EPA's most current voluntary consensus-based standards.

“Any mitigation measures taken or system installed in your home must conform to your state's regulations. In states without regulations covering mitigation, EPA recommends that the system conform to EPA's most current voluntary consensus-based standards.”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

EPA recommends that the mitigation contractor review the radon measurement results before beginning any radon-reduction work.

“EPA recommends that the mitigation contractor review the radon measurement results before beginning any radon-reduction work.”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

The Home Buyer's and Seller's Guide says a qualified contractor should be able to, among other things, review testing guidelines and measurement results and determine if more measurements are needed, and give you a detailed, written proposal on how radon levels will be lowered.

“A qualified radon-reduction (mitigation) contractor should be able to: Review testing guidelines and measurement results, and determine if additional measurements are needed; Evaluate the radon problem and provide you with a detailed, written proposal on how radon levels will be lowered;”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

A potential conflict of interest exists if the same person or firm does the testing and installs the mitigation system. Some states may require the homeowner to sign a waiver in such cases.

“Be aware that a potential conflict of interest exists if the same person or firm performs the testing and installs the mitigation system. Some states may require the homeowner to sign a waiver in such cases.”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

The guide says to choose a radon contractor as you would for other home repairs: it is wise to get more than one estimate, ask for references, and contact some of those references.

“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 contractor's work.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Many contractors give free estimates but 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 house structure or the anticipated degree of difficulty.

“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 house structure or the anticipated degree of difficulty.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

When comparing proposed costs, the guide says to consider what you get for your money; for example, a less expensive system may cost more to operate and maintain.

“Compare the contractor's proposed costs and consider what you get for your money, taking into account: a less expensive system may cost more to operate and maintain;”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Ask the contractor to prepare a contract before any work starts, read it before you sign it, and make sure everything in it matches the original proposal.

“Ask the contractor to prepare a contract before any work starts. Read the contract before you sign it. Make sure everything in the contract matches the original proposal.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Many contractors provide a guarantee to adjust or modify the system to reach a negotiated radon level (the guide's example is 2 pCi/L or less). The guide says to read carefully the contract conditions describing the guarantee.

“Many contractors provide a guarantee that they will adjust or modify the system to reach a negotiated radon level (e.g., 2 pCi/L or less). Carefully read the conditions of the contract describing the guarantee.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Among the important information the guide says should appear in the contract is a declaration stating whether any warranties or guarantees are transferable if you sell your home.

“A declaration stating whether any warranties or guarantees are transferable if you sell your home.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Some techniques prevent radon from entering the home while others reduce radon levels after it has entered. EPA generally recommends methods that prevent the entry of radon.

“Some techniques prevent radon from entering your home while others reduce radon levels after it has entered. EPA generally recommends methods that prevent the entry of radon.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Soil suction prevents radon from entering by drawing it from below the home and venting it through a pipe, or pipes, to the air above the home, where it is quickly diluted.

“Soil suction, for example, prevents radon from entering your home by drawing the radon from below the home and venting it through a pipe, or pipes, to the air above the home where it is quickly diluted.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

If the contractor's visual inspection fails to provide enough information, the contractor may need to perform diagnostic tests during the initial phase of the installation.

“If this inspection fails to provide enough information, the contractor may need to perform diagnostic tests during the initial phase of the installation to help develop the best radon reduction system for your home.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Active subslab suction, also called subslab depressurization, is described as the most common and usually the most reliable radon reduction method.

“Active subslab suction — also called subslab depressurization — is the most common and usually the most reliable radon reduction method.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

In an active system, 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 creating a negative pressure or vacuum beneath the slab.

“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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Passive subslab suction is the same as active subslab suction except that it relies on natural pressure differentials and air currents instead of a fan.

“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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Passive subslab suction is generally not as effective in reducing high radon levels as active subslab suction.

“Passive subslab suction is generally not as effective in reducing high radon levels as active subslab suction.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Where a basement home has a sump pump, the sump can often be capped so that it can continue to drain water and serve as the location for a radon suction pipe.

“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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Sealing cracks and other openings in the foundation is a basic part of most approaches, but EPA does not recommend sealing alone to limit radon entry, because sealing alone has not been shown to lower radon levels significantly or consistently.

“Sealing cracks and other openings in the foundation is a basic part of most approaches to radon reduction. EPA does not recommend the use of sealing alone to limit radon entry. Sealing alone has not been shown to lower radon levels significantly or consistently.”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

In crawlspace homes, an effective method covers the earth floor with a high-density plastic sheet; a vent pipe and fan draw the radon from under the sheet and vent it to the outdoors.

“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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

This form of soil suction is called submembrane suction, and when properly applied it is the most effective way to reduce radon levels in crawlspace homes.

“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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Active crawlspace depressurization, which draws air directly from the crawlspace with a fan, is called a less-favorable option. It generally does not work as well as submembrane suction and requires special attention to combustion appliance backdrafting and to sealing the crawlspace from the rest of the home.

“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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

House or room pressurization uses a fan to blow air into the basement or living area. It generally brings more outdoor air into the home, which can cause moisture intrusion and energy penalties, so the guide says it should only be considered after the other, more-common techniques have not sufficiently reduced radon.

“House 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 opened, 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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

A heat recovery ventilator (HRV) can be designed to ventilate all or part of a home, but HRVs are more effective in reducing radon levels when used to ventilate only the basement.

“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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Once windows, doors and vents are closed, radon concentrations most often return to previous values within about 12 hours. The guide says natural ventilation should normally be regarded as only a temporary radon reduction approach, because of the disadvantages it lists: loss of conditioned air and related discomfort, greatly increased costs of conditioning additional outside air, and security concerns.

“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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

The Consumer's Guide says 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.

“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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

The Consumer's Guide says radon reduction systems must be clearly labeled, to avoid accidental changes to the system that could disrupt its function.

“Radon reduction systems must be clearly labeled. This will avoid accidental changes to the system that could disrupt its function.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

The Consumer's Guide says 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 radon to reenter the home, if the pipes do not vent at least 2 feet above these openings.

“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 radon to reenter the home, if the exhaust pipes do not vent at least 2 feet above these openings.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

The Consumer's Guide says the exhaust fan must not be located in or below a livable area; for instance, it should be installed in unconditioned space.

“The exhaust fan must not be located in or below a livable area. For instance, it should be installed in unconditioned space.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

The Consumer's Guide says a warning device must be installed to alert you if an active system stops working properly.

“A warning device must be installed to alert you if an active system stops working properly.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

The Consumer's Guide says a post-mitigation radon test should be done within 30 days of system installation, but no sooner than 24 hours after the system is in operation with the fan on, if it has one.

“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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

The contractor may do a post-mitigation test, but the guide recommends that you also get an independent follow-up radon measurement: an independent tester, or measuring yourself, will eliminate any potential conflict of interest. A two- to seven-day measurement is recommended to test the system's effectiveness.

“The contractor may perform a post-mitigation test to check his work and the initial effectiveness of the system; however, it is recommend 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.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

For that test, the guide's test conditions say windows and doors must be closed 12 hours before and during the test, except for normal entry and exit.

“Test conditions: windows and doors must be closed 12 hours before and during the test, except for normal entry and exit.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

If you have a fan powered (or active) system, you should look at your warning device, usually a manometer, on a regular basis to make sure the system is working correctly.

“If you have a fan powered (or active) system, you should look at your warning device, usually a manometer, on a regular basis to make sure the system is working correctly.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

The fan should never be turned off; the guide says it must run continuously for the system to work correctly.

“Remember, the fan should NEVER be turned off; it must run continuously for the system to work correctly.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Fans may last for five years or more and may then need to be repaired or replaced; manufacturer warranties tend not to exceed five years.

“Fans may last for five years or more — manufacturer warranties tend not to exceed five years — and may then need to be repaired or replaced.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

The guide says it is a good idea to retest your home at least every two years to be sure radon levels remain low.

“It is a good idea to retest your home at least every two years to be sure radon levels remain low.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Before major structural changes after a system is installed, such as converting an unfinished basement into living space, ask your radon contractor whether the changes could void any warranties.

“If you decide to make major structural changes to your home after you have had a radon reduction system installed, such as converting an unfinished basement area into living space, ask your radon contractor whether these changes could void any warranties.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

After you remodel, retest in the lowest lived-in area to make sure the construction did not reduce the effectiveness of the radon reduction system.

“After you remodel, retest in the lowest lived-in area to make sure the construction did not reduce the effectiveness of the radon reduction system.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

If you are selling a home that has a radon reduction system, the guide says to inform potential buyers and supply them with information about the system's operation and maintenance.

“If you are selling a home that has a radon reduction system, inform potential buyers and supply them with information about your system's operation and maintenance.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Even if built to be radon-resistant, every new home should be tested for radon as soon as possible after occupancy. With a result of 4 pCi/L or more, a vent fan can easily be added to the passive system to make it an active system.

“Even if built to be radon-resistant, every new home should be tested for radon as soon as possible after occupancy. If you have a test result of 4 pCi/L or more, a vent fan can easily be added to the passive system to make it an active system and further reduce radon levels.”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

Building radon-resistant features into the house during construction is described as easier and cheaper than fixing a radon problem from scratch later.

“Building radon-resistant features into the house during construction is easier and cheaper than fixing a radon problem from scratch later.”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

Building codes in your state or local area may require radon-resistant construction features. If you are buying or renting a new home, the guide says to ask the owner or builder if it has radon-resistant features.

“Building codes in your state or local area may require these radon-resistant construction features. If you are buying or renting a new home, ask the owner or builder if it has radon-resistant features.”

EPA: A Citizen's Guide to Radon (EPA 402/K-12/002, 2025 edition)

A gas-permeable layer is placed beneath the slab or flooring system so soil gas can move freely underneath the house. It is used only in homes with basement and slab-on-grade foundations, not in homes with crawlspace foundations.

“This layer is placed beneath the slab or flooring system to allow the soil gas to move freely underneath the house. In many cases, the material used is a 4-inch layer of clean gravel. This gas-permeable layer is used only in homes with basement and slab-on-grade foundations; it is not used in homes with crawlspace foundations.”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

Plastic sheeting is placed on top of the gas-permeable layer and under the slab to help prevent soil gas from entering. In crawl spaces, the sheeting (with seams sealed) is placed directly over the crawlspace floor.

“Plastic sheeting is placed on top of the gas-permeable layer and under the slab to help prevent the soil gas from entering the home. In crawl spaces, the sheeting (with seams sealed) is placed directly over the crawlspace floor.”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

A 3- or 4-inch PVC pipe (or other gas-tight pipe) runs from the gas-permeable layer through the house to the roof, to safely vent radon and other soil gases to the outside.

“A 3- or 4-inch PVC pipe (or other gas-tight pipe) runs from the gas-permeable layer through the house to the roof, to safely vent radon and other soil gases to the outside.”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

An electrical junction box is included in the attic to make wiring and installing a vent fan easier, for example if you decide to activate the passive system because a test showed an elevated radon level (4 pCi/L or more).

“An electrical junction box is included in the attic to make the wiring and installation of a vent fan easier. For example, you decide to activate the passive system because your test result showed an elevated radon level (4 pCi/L or more).”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

If you have tested for radon in air and have elevated levels, and your water comes from a private well, the guide says to have your water tested.

“If you've tested for radon in air and have elevated radon levels and your water comes from a private well, have your water tested.”

EPA: Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001, revised March 2024)

Most of your risk from radon in water comes from radon released into the air when water is used for showering and other household purposes.

“Most of your risk from radon in water comes from radon released into the air when water is used for showering and other household purposes.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Point-of-entry treatment for the whole home can effectively remove radon from the water before it enters the home's water distribution system, usually with either granular activated carbon (GAC) filters or aeration systems.

“Point-of-entry treatment for the whole home can effectively remove radon from the water before it enters your home's water distribution system. Point-of-entry treatment usually employs either granular activated carbon, or GAC, filters or aeration systems.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)

Point-of-use devices remove radon at the tap but only treat a small portion of the water you use, and they are not effective in reducing the risk from breathing radon released into the air from all water used in the home.

“Point-of-use treatment devices remove radon from your water at the tap, but only treat a small portion of the water you use, such as the water you drink. Point-of-use devices are not effective in reducing the risk from breathing radon released into the air from all water used in the home.”

EPA: Consumer's Guide to Radon Reduction (EPA 402/K-10/005, 2025 edition)