Last post we discussed Radon. What it is, where it comes from and its associated health risks. Now let’s talk a little about what to do if your home has elevated levels of radon. The next step is called mitigation. Mitigation is defined as a way to moderate the intensity or force of something, and in many cases alleviate the thing all together. When the something is radon, mitigation means utilizing one or more accepted techniques to reduce radon levels inside a home and lessen the risk of exposure to the home’s occupants. The goal of radon mitigation is to reduce the radon concentration in a home to a safe level and prevent radon concentrations from being elevated in the future.
Of course a homeowner’s biggest concern is cost. The good news is the cost to fix a home with elevated levels of radon is on average between $800 and $2500 depending on the age, style, location, overall condition and type of reduction system chosen. The EPA estimates that the average cost of a radon reduction system is about $1200.
The foundation of the home will dictate which technique will work the best. There are three basic types of foundations; basement, slab-on-grade, and crawlspace. For basements and slab-on-grade one of the most effective methods is called soil suction. This method actively or passively draws radon from the ground underneath the house and vents it away. One of the more common and reliable active soil suction methods is called sub- slab depressurization. In this technique a suction pipe or pipes is inserted through the slab and into the gravel or soil underneath. A vent fan is then connected to the pipe (usually in the attic) to draw the radon gas from underneath the house and into the air outside through the roof. This same method is available in a passive mode in which there is no fan instead natural air currents are used to draw the radon gas up and out of the house. This technique is not as effective as its active counterpart but it is less expensive up front as well as in the long run because of the absence of the fan. The passive system is typically what contractors install when they build a home with radon-resistant features. Of course a fan can always be added later if need be. Some basements are hollow block foundations rather than poured concrete. In these cases, block wall suction (similar to sub- slab suction) is used to remove radon and depressurize the block wall. A combination of block wall suction and sub- slab suction can be utilized if necessary.
Reducing radon levels in a home with a crawlspace can best be accomplished with a technique called sub- membrane suction in which a perforated pipe is first placed on the floor of the crawlspace to collect the gas from the soil. Then the ground is covered with high density plastic that is sealed along the edges and seams. The plastic sheeting traps the radon between the ground and the sheet, and a vent pipe and fan are used to draw it from under the sheet and vent it to the outdoors. Whatever method(s) is used sealing and calking cracks in the foundation will increase their effectiveness by limiting radon entry.
While I hope this helps give a better understanding of the accepted radon mitigation techniques commonly used today there are many variations of the above mentioned methods. For a more detailed discussion please read Standard Practice for Installing Radon Mitigation Systems in Existing Low-Rise Residential Buildings, 402K03007 – ASTM 2121, available through the EPA’s website.