Numerical modelling is necessary in order to better understand transient phenomena of radon transport from radium-contaminated soils to a house basement where high radon levels were observed. The present work aims to develop a robust and simplified subsurface numerical model which can simulate radon transport at the soil-basement foundation interface under variable weather conditions around a house. The equivalent continuum modelling (ECM) approach has been used assuming an equivalent porosity and permeability of the basement foundation cracked concrete materials. This approach has been applied for simulating two-dimensional (2D) soil-gas and radon-entry into a house basement built on sand contaminated by uranium mill tailings (UMT) considering the presence of an aquifer with water-table, rainfall, evapotranspiration, atmospheric air pressure, and house under-pressurization. Sensitivity analysis of the model foundation parameters, performed at steady-state, showed that the numerical model predictions at transient conditions were in a good agreement with measurements of the radon-entry-rate through the basement foundation and radon concentration in the basement. The optimized parameters are physically sound and consistent with the observations and literature data. © 2017 Elsevier Ltd.