Radon is a well-known risk and, as the second leading cause of lung cancer in the U.S., has a high potential for intrusion for properties everywhere. Various factors influence radon levels in a building such as the strength of the source (e.g., how much uranium/radium is in the soil); porosity of the soil; building construction and foundation type (e.g., basement, crawlspace, slab-on-grade construction); weather conditions (e.g., wind, temperature, and barometric pressure); and occupant activity.
The amount of uranium/radium in the local soil and/or bedrock underlying a property can affect the amount of radon gas that is available and potentially able to mitigate into buildings. The 1993 United States Environmental Protection Agency (EPA) Map of Radon Zones (see below) depicts areas of the country where elevated radon concentrations may be present based on the subsurface geology (i.e., soils and bedrock). In addition, the type of soil and bedrock can influence the ability of radon gas to migrate up through the ground surface and potentially into a building.
Building construction can also affect radon levels that may be present in a building. Below grade levels can accumulate elevated radon due to the direct contact with soil and/or bedrock. Properly vented crawlspaces can help mitigate radon gas by allowing the radon to dissipate through vents. The condition of the building floor slabs and foundations can be a contributing factor for radon gas migration. A floor slab in poor condition (e.g., cracks, unsealed penetrations, etc.) provides a direct pathway for radon gas to enter a building. In addition, gaps between foundations and floor slabs can be an additional pathway for radon gas.
Radon concentrations typically vary seasonally due to weather conditions. In northern climates, during the spring and fall, and possibly summer months, the windows of buildings may be open more. This allows radon to dissipate through the open windows and can reduce indoor radon gas concentrations. During winter months and hotter summer months, building occupants may keep windows closed and use heat or air conditioning more. The closed building condition can allow radon gas to accumulate inside a building and not have a ready path to leave or dissipate.
While everyone has experienced some exposure to radon, it is less concerning outdoors as it dilutes quickly to low concentrations. However, the longer an occupant spends in a building with elevated radon gas, typically, the higher their exposure and chance for adverse health effects. An individual that spends more time in a basement of a building with a cracked floor slab may have a higher rate of exposure than an individual who has more intermittent time in a lower level of a building.
Understanding the potential radon risks early in the project will help to manage the cost implications and minimize delays. Adding a team with the expertise and resources to effectively address these items will further the potential for successful project outcomes. Please join Derek Schilling and Stephen Jansen from Braun Intertec for our live webinar, “Radon Measurement and Mitigation Considerations and Strategies for Affordable Housing Projects” on October 21, 2021.