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  • House Foundation Types

Your house type will affect the kind of radon reduction system that will work best. Houses are generally categorized according to their foundation design. For example: basement, slab-on-grade (concrete poured at ground level), or crawlspace (a shallow unfinished space under the first floor). Some houses have more than one foundation design feature. For instance, it is common to have a basement under part of the house and to have a slab-on-grade or crawlspace under the rest of the house. In these situations a combination of radon reduction techniques may be needed to reduce radon levels to below 4 pCi/L.

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Figure 179: Your house type will affect the kind of radon reduction system that works best. Houses are generally categorized according to their foundation design.

Radon reduction systems can be grouped by house foundation design. Determine your type of foundation design and read about which radon reduction systems may be best for your house.

  • Basement and Slab-on-Grade Houses

In houses 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, or block wall suction.

subslab suction

Figure 180: Active Subslab suction (also called subslab depressurization) is 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. 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 house. 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 pipe(s) draws the radon gas from below the house and releases it into the outdoor air while simultaneously creating a negative pressure (vacuum) beneath the slab. Common fan locations include unconditioned house and garage spaces, including attics, and the exterior of the house.

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 house. Passive subslab suction is usually associated with radon-resistant features installed in newly constructed homes.  Passive subslab is generally not as effective in reducing high radon levels as active subslab suction.

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

One variation of subslab and drain tile suction is sump hole suction. Often, when a house 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 an be used in basement houses 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 Houses

An effective method to reduce radon levels in crawlspace houses 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 sub membrane suction, and when properly applied is the most effective way to reduce radon levels in crawlspace houses.  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 sub membrane suction and requires special attention to combustion appliance back drafting and sealing the crawlspace from other portions of the house, and may also result in increased energy costs due to loss of conditioned air from the house.

In some cases, radon levels can be lowered by ventilating the crawlspace passively (without the use of a fan) 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 house.  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 house.

  • Other Types of Radon Reduction Methods

Other radon reduction techniques that can be used in any type of house include: sealing, house/room pressurization, heat recovery ventilation, and natural ventilation.

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 house opens new entry routes and reopens old ones.

House/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 house. The effectiveness of this technique is limited by house construction, climate, other appliances in the house, 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.

A heat recovery ventilator (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 houses 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 (see the EPA Installation and Operating Cost Table Figure 182).

Some natural ventilation occurs in all houses.  By opening windows, doors, and vents on the lower floors you increase the ventilation in your house.  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 house 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.

  • 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 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.

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

  • The exhaust pipe(s) of soil suction systems must vent above the surface of the roof and 10 feet or more above the ground, and at least 10 feet away from windows, doors, or other openings that could allow the radon to reenter the house, if the exhaust pipe(s) 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 in an unoccupied attic of the house or outside - not in a basement!

  • 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 (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 2-7 day measurement is recommended.  Test conditions:  windows and doors must be closed 12 hours before and during the test, except for normal entry/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.

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