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Revisions proposed for Canada's National Building Code to address
Health Canada's new radon guideline
http://irc.nrc-cnrc.gc.ca
Revisions propose d for Ca na da ’s N at iona l Building Code t o
a ddre ss H e a lt h Ca na da ’s ne w ra don guide line
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21, (5), pp. 2
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Revisions proposed for Canada’s National Building Code to address Health Canada’s new radon guideline
By Frank Lohmann
This article discusses the reduction in the Health Canada accepted level of radon exposure in homes and reviews proposed changes (a rough-in requirement for a future exhaust system) to the National Building Code developed to accommodate this reduction.
Radon is a colourless, odourless, radioactive gas that occurs naturally in the environment. Outdoors, it mixes with air and concentrations are therefore negligible. But when it enters an enclosed space, such as a building, it can
accumulate to high levels and become a health concern. In fact, scientific studies have conclusively linked long-term exposure to high levels of radon with lung cancer. According to Health Canada, that risk is increased for smokers. Radon primarily seeps from the soil into buildings through sump holes, dirt floors, floor drains, and cinder block walls, but soil gas with a high radon concentration may also travel through cracks in foundations and concrete floors. As a result, the gas concentrates mostly in basements or first floors. Although concrete slab basements allow for less soil gas entry than do unfinished dirt-floor basements, both types of surfaces can permit radon entry.
Explicit requirements for soil gas mitigation, including radon, have been in Canada’s National Building Code (NBC) since 1995. Other requirements such as damp proofing, good concrete quality, excavations free of organic material, and ventilation also contribute to reducing the risk of radon entry into basements. The 2005 edition of the NBC furthermore includes minimum requirements such soil gas barriers (the sealing of the perimeter of slabs-on-ground and the sealing of penetrations through slabs such as floor drains), as well as sub-floor depressurization and ventilation in buildings.
The 2005 edition, however, references Health Canada’s 1990 radon guideline, which sets the acceptable level of radon exposure for indoor air at 800 becquerel/m³ (Bq/m³). Review of the studies linking radon to lung cancer prompted the federal government to review this guideline in collaboration with provincial and territorial governments and in 2007, through Health Canada, reduce the guideline for acceptable radon levels within buildings from 800 Bq/m³ to 200 Bq/m³. This guideline addresses new and existing construction where the building is occupied for more than four hours a day. It is in line with the limit set by the Environmental Protection Agency (EPA) in the U.S. and with those of most other countries.
Even before the guideline was reduced, the Standing Committees of the Canadian Commission on Building and Fire Codes (CCBFC), which develops the NBC, were discussing proposed changes to specifically address radon ingress, and the process of establishing a task group to review current requirements in the NBC was already underway. Once established, the task group determined that no technical changes were needed to current air barrier and sealing requirements. They recommended a simple restructuring of existing requirements to improve their effectiveness and applicability to all homes across the country. The recommendations included moving sealing and soil gas control requirements to the section dealing with air barriers to increase their visibility and emphasize that air barriers included those below ground as well as above.
To bring the NBC in line with the new Health Canada guideline, the task group recommended that, even though no technical changes were necessary, a rough-in requirement for a future exhaust system, in addition to a good air barrier system in below-ground assemblies, be added. This would facilitate post-construction radon removal should that subsequently prove necessary. It would also resolve confusion created in applying the current code, which in one section states that every house should be protected, and in another part states that where it could be demonstrated that radon was not a problem, no action was required.
Radon levels in homes vary considerably owing to a variety of factors such as local geology, building
design/operation, and seasonal environmental factors. These factors also vary widely from one house to another even if the two are similar and next door to each other. In addition, radon can only be determined to be a problem after a house is finished and occupied, when all the walls and windows are in, and the house is being used in a normal fashion. As a result, once radon is determined to be a problem, it is usually too late, and too costly, to add the infrastructure to remove it. Requiring that every new home be equipped with the rough-in to eliminate radon gas would ensure that, should it prove necessary, mitigation could be easily and cost-effectively carried out.
The proposed changes will be submitted to a public review in September 2009 and, if approved, will be included in the 2010 edition of the NBC.
For more information on these proposed changes, contact Frank Lohmann at the NRC Institute for Research in Construction (phone: 613-993-9599, or e-mail frank.lohmann@nrc-cnrc.gc.ca).
Frank Lohmann is a technical advisor in the Canadian Codes Centre at the NRC Institute for Research in Construction.
