Radon resistance

Common Masonry Wall Details and Their Impact on Radon Resistance. .. 1275... 

Growing concern about the risks posed by indoor radon has underscored the need for dependable radon-resistant residential construction techniques. In response to this public health exposure, the U.S. EPA has developed and demonstrated a variety of methods that have been used to reduce radon levels in existing homes.2,8 Many of these methods could be applied during construction, involve less labor and financial investments, and provide greater homeowner satisfaction and safety than would a radon-reduction technique installed after the home is built and occupied. 

This chapter is designed to provide homeowners and builders with an understanding of operating principles and installation details of the construction of a new radon-resistant home. This chapter should provide a basic understanding of the types of products and systems that are available and being used. In this way, the reader will be able to select the radon-resistant products and systems that will be best applicable to a particular situation. 

FIGURE 31.1 Radon decay showing half-lives of products. (Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.)... 

The question most often asked by homebuilders is Can one determine whether radon-resistant construction techniques should be applied to a given site ... 

U.S. EPA does not recommend the avoidance of building sites that are suspected to contain strong radon it does, however, strongly recommend that the homes built on those sites be designed and built with radon-resistant construction techniques.9... 

The following sections contain recommended radon-resistant construction techniques that a builder may wish to incorporate into the home. It should be understood that these are recommendations only and should not be construed as guidelines or regulations. The recommendations are based on the best available information gathered from numerous research projects.9... 

Below-grade walls may be constructed of poured concrete, masonry blocks, or other materials such as all-weather wood or stone. This chapter discusses details for use of poured concrete and masonry foundation because these are the materials most commonly used for new construction. Recently, trade associations such as American Plywood Association (APA) and the National Forest Products Association (NFoPA) have issued publications on designing radon resistance permanent wood foundations. Information on these types of foundations can be found by contacting the appropriate trade association.21... 

The application of dampproofing and waterproofing materials on the exterior, interior, or both sides of the foundation that can serve as a radon-resistant barrier is recommended to help control radon entry. It must be understood that a coating applied to a foundation intended to resist the flow of radon into the building is in addition to the normal waterproofing/dampproofing requirements. 

Coatings are applied to the outside or inside of the foundation, creating a radon-resistant barrier between the source and the inside of the home. They come in a wide variety of materials including paint-like products that can be brushed on the interior of the foundation, tar-like materials that are applied to the outside, and cementitious materials that can be brushed or troweled on. They cannot be applied to the underside of the concrete floor slab for obvious reasons, so they must be applied to the inside surface of the slab. The effective life of an interior coating can be greatly diminished by damage therefore, care must be taken to provide protection to the material used. 

The next four sections contain details for a deeper understanding of radon-resistant construction issues. The four major topics are... 

In theory, the application of radon barriers should be adequate to avoid elevated radon levels in houses. In practice, however, a backup radon mitigation system has been found essential for maintaining indoor radon concentrations below 4 pCi/L in most homes studied. In the recent radon-resistant residential construction projects conducted by U.S. EPA and/or private builders, several of the homes designed to be radon resistant have contained radon concentrations above 4 pCi/L. In each of those houses, a backup system consisting of an active (fan-assisted), or passive (wind-and-stack-effect-assisted), SSD system was installed at the time of construction. When mechanical barriers failed to adequately control radon, the soil depressurization methods were made operational. 

Due to difficulties often encountered in sealing subfloors and insulating pipes in crawlspace houses, which rarely have a poured floor slab, another radon-resistant alternative that can be applied after construction should be considered. This mitigation technique is a variation of the successful SSD methods used in basements. Polyethylene sheeting is often used as a moisture barrier applied directly over the soil in crawlspaces. The polyethylene sheeting can be used as a gastight barrier that forms a small-volume plenum above the soil where radon collects. A fan can be installed to pull the collected soil gas from under the sheeting and exhaust it outside the house. 

Some builders prefer to concrete the floor of crawlspaces when site and design conditions permit getting the mix into the crawlspace. If a crawlspace has a concrete slab, for radon-resistant construction, the crawlspace should be treated similar to a basement with the advantage of greater ventilation potential. 

Ongoing U.S. EPA research on radon-resistant new construction has encountered numerous difficulties in making a gastight mechanical barrier effective enough to confidently keep indoor radon levels below 4pCi/L. The types of problems encountered included... 

The perimeter crack is located between the edge of the floor slab and the foundation wall. This applies to slabs in basements, crawlspaces, and slab-on-grade foundations. As a cold joint, this perimeter crack is always a potential radon entry point. Contractors building radon-resistant houses... 

Other radon-resistant alternatives besides simple isolation of the crawlspace should be considered because of the difficulties encountered in getting an adequate seal between the house and the crawlspace. These alternatives will be discussed in the next section. 

If waterproofing or dampproofing treatments that are effective gas barriers and that can be sealed at joints and penetrations could be identified, then walls could be made radon resistant. Acceptable dampproofing or waterproofing treatments are specifically listed in building codes in many areas of the United States these lists are periodically amended as new materials come into use. These coatings apply primarily to basement walls. 

Construction film is already in common use as a subslab vapor barrier in many areas of the country. The current prevalence and low cost of this material mean that it may be worthwhile to continue its use even though it is an imperfect barrier. It is possible to seal polyethylene vapor barriers at the overlapped edges, at penetrations, and at the footing but it may be that the extra effort will not be rewarded with improved radon resistance. 

Using the permeability and soil radon measurements for the gravel soils in New York State to compare with the Swedish guidelines would result in a recommendation for radon-resistant techniques to be used in a large fraction of new houses in all the areas listed, except Long Island. 

In U.S. EPA Office of Radiation Program s New House Evaluation Program (NEWHEP), two builders in the Denver area, two in Colorado Springs, and one in Southfield, Michigan, installed various radon-resistant features in houses during construction. A sampling of subsequent measurements of indoor radon, adjacent soil gas radon, and soil radium content is summarized in Table 31.6.36... 

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