Indoor radon trends with building code change in two Canadian cities

Radon studies were conducted in two Canadian cities, in Halifax, Nova Scotia, and Winnipeg, Manitoba, to evaluate trends in indoor radon before and after the 2010 National Building Code of Canada was adopted into the legally binding provincial building codes in 2011. Participants were recruited in neighbourhoods characterized by newer housing developments. A postcard campaign in each city offered free radon testing to every house in the target areas, and free testing kits were mailed to study participants. Indoor radon measurements and house questionnaires were completed by 225 eligible participants in Halifax and 171 eligible participants in Winnipeg, using alpha-track radon detectors deployed for three months during the heating season in 2021-2022. Multivariate logistic regression analyses were conducted to evaluate the association between indoor radon and the period of construction, the area in contact with the ground, the number of storeys, the type of heating system, the water source, and the type of ventilation. These analyses were focussed on the detached study houses because the majority of the participants lived in a detached house, and significant associations were identified for the period of construction and the floor where the radon detector was located. An odds ratio of 1.91 (1.04-3.50) for the detached Halifax study houses built after 2011 was associated with having a higher than geometric mean radon concentration (p = 0.033), nearly double the likelihood. There was no evidence of significant change in the indoor radon after 2011 in the detached Winnipeg study houses. A lower likelihood - almost half - for measurement conducted on a main/upper floor compared to in the basement was associated with a radon concentration above the respective geometric mean for each city: an odds ratio of 0.48 (0.27-0.86) for the detached Halifax study houses (p = 0.012), and of 0.45 (0.32-0.64) for the detached Winnipeg study houses (p = 0.022). Radon is the second most important cause of lung cancer, after smoking, and the results of this study support strengthening the radon preventive measures required in new low-rise housing to reduce the associated lung cancer burden in Canada.