Radon mitigation options for existing buildings

Note: The ICS Code, scope and project need for this NOI (originally published on January 11, 2022) was updated by the responsible SDO on March 19, 2024.

Note: The title and scope for this NOI (originally published on  January 11, 2022) were updated by the responsible SDO on June 20, 2023.

1. Scope

This National Standard of Canada provides details on two types of radon mitigation system that can be selected based on the conditions present in and around an existing building¹.

Active soil depressurization (ASD) systems²  – ASD systems utilize a fan to create negative pressure on the soil side relative to the interior of the building and exhaust the radon-laden soil gas to the outdoors where it is rapidly diluted. ASD systems may reduce indoor radon gas concentrations by 50 to 99%. ASD is the preferred method of reducing radon in a building, when practical and installed according to this standard and best practices. It has been shown to be able to reduce radon levels significantly and it is simple and easy to maintain.

Ventilation systems – Reduction of radon gas concentrations in a building can also be achieved through dilution of indoor air using balanced ventilation systems as provided by example systems such as a heat recovery ventilator (HRV) or an energy recovery ventilator (ERV). Balanced ventilation systems in airtight buildings have been shown to reduce indoor radon gas concentrations by an average of 20 to 50%. Ventilation can be used as a supplemental option or in certain circumstances, where ASD systems are not practical. Ventilation effectiveness can be influenced by several factors of building use and can decline in effectiveness if not properly maintained, and therefore should include a system where radon levels are continuously monitored.

When applying either mitigation technique, sealing of the slab and other entry points for radon gas is necessary.

Units of measurement – Quantities and dimensions used in this standard are provided in units from the International System of Units (SI units). Imperial equivalents may be shown in brackets, if applicable.

1.1       Application to building types

The technical provisions for radon mitigation in this standard originate from the successful application of the standard to single family dwellings. There exist known instances where the technical principles of this standard have been applied to other National Building Code of Canada (NBC) part 9 building types (e.g., semi-detached homes, townhomes, and other low-rise buildings) and schools. Therefore, under certain conditions, the technical principles in this standard may be applicable to buildings other than single family dwellings.

Buildings are to be considered as systems. Where a building includes two or more buildings/units that share a common foundation without footings or structural features that prevent airflow across the full foundation, work to reduce indoor radon gas concentrations should be undertaken to reduce concentrations as low as reasonably achievable in all buildings/units. However, the mitigation techniques should include accessing each building unit and proper labeling in all units. In such cases where access to each building/unit is restricted due to lack of permission, radon mitigation should be done to limit its impact to only the buildings/units that are accessible. The standard includes a communication test that will determine the effectiveness of an ASD system prior to installation. If this test indicates that any basic system may not be effective, the principles included in the standard can provide guidance for designing effective radon control solutions for non-typical buildings.

This standard is not intended to provide an acceptable solution to every type of building; rather the technical principles included in this standard can provide base requirements for designing radon mitigation solutions for non-typical buildings. Further guidance regarding radon mitigation standards for schools and large buildings is provided in “RMS-LB 2018 with 12/20 revisions”. Guidance regarding radon mitigation standards for multifamily buildings is provided in ANSI/AARST standard RMS-MF 2014 entitled Radon Mitigation Standards for Multifamily Buildings.

1.2       Limitation

The application of the requirements found in this standard cannot guarantee radon reduction neither below the Canadian radon guideline nor can it predict a desired post-mitigation radon concentration. Factors such as complex building configuration, building deterioration or accessibility issues may impair the application of some requirements and may reduce their efficiencies.

This standard provides a communication test, system design and installation instructions, and acceptable materials and product specifications to optimize the capacity of the mitigation system to reduce indoor radon gas concentrations.

This standard is specific to radon gas infiltrating into a building from the ground.

1.3       Exclusions

This standard does not address the mitigation techniques for radon from water and construction materials (see Annex C).

The radon gas control measures presented in this standard may not be appropriate for the mitigation of radon gas in new buildings (see CAN/CGSB-149.11, Radon control options for new buildings).

This standard does not address the control and mitigation of radon gas in all types of buildings. Additional details may be required for the installation in specific building types or building configurations (for example, application of this standard to some large buildings may not be appropriate).

Note: Work is typically undertaken, solely or in combination, by registered professionals possessing expertise in reducing radon gas ingress, C-NRPP certified practitioners/specialists or those permitted by the authority having jurisdiction.

This standard does not address mitigation techniques that involve depressurization of crawlspaces.

The testing and evaluation against this standard may require the use of materials and/or equipment that could be hazardous. This standard does not purport to address all the safety aspects associated with its use. Anyone using this standard has the responsibility to consult the appropriate authorities and to establish appropriate health and safety practices in conjunction with any applicable regulatory requirements prior to its use.

[1] For this standard and CAN/CGSB-149.11, an existing building is considered a building which has been completed and is either currently occupied or ready for occupancy.

2 In CAN/CGSB-149.11, ASD systems are considered a Level 3 system. CAN/CGSB-149.11 references this standard for details on the installation of a Level 3 system.