Radon is a radioactive gas produced by the decay of uranium-238 in rocks and soils. Residential buildings represent the main source of human exposure to radon. This study evaluates indoor radon exposure and associated health risks in residential buildings in Masha town, South Wollo, Ethiopia. Indoor radon-222 activity concentrations were measured in 21 dwellings using a Corentium digital radon detector based on alpha spectroscopy. The measured concentrations ranged from\(\:\:6.66\pm\:0.46Bq\:{m}^{-3}\) to \(\:141.71\pm\:9.92\:Bq\:{m}^{-3}\). Buildings constructed with mud walls and earthen floors exhibited the highest mean radon concentration (\(\:93.08\pm\:6.52\:Bq{\:m}^{-3}\)), followed by houses with mud interiors, concrete exteriors, and concrete floors (\(\:80.66\pm\:5.65\:Bq\:{m}^{-3}\)). In contrast, structures built with concrete block walls and floors showed lower average concentrations (\(\:37.72\pm\:2.64\:Bq{\:m}^{-3}\)), while reinforced concrete buildings recorded the lowest levels (\(\:26.83\pm\:1.88\:Bq\:{m}^{-3}\)). Notably, 57.15% of mud-walled, earthen-floored houses exceeded the World Health Organization recommended reference level of\(\:100\:Bq{\:m}^{-3}\). The estimated annual effective inhalation dose ranged from\(\:\:0.168\:mSv{y}^{-1}\) to\(\:\:3.582\:mSv{y}^{-1}\), with corresponding equivalent lung doses between \(\:0.403\:mSv{y}^{-1}\) and\(\:\:\:8.582mSv{y}^{-1}\). These exposure levels were associated with a relative lung cancer risk ranging from 1.006 to 1.132, with an average value of 1.055. Elevated radon concentrations were linked to factors such as permeable soil conditions, the use of construction materials derived from uranium-rich bedrock, and structural defects including foundation cracks. Overall, the findings indicate that building characteristics play a significant role in indoor radon accumulation and associated health risks. It is therefore recommended that radon-resistant construction practices, improved ventilation, and regular monitoring be implemented.
