Estimating the importance of factors influencing the radon-222 flux from building walls

► We study factors affecting the Wall Radon exhalation Flux (WRF). ► We estimate that a significant risk arises when WRF exceeds 10 × 10− 3 Bq·m− 2·s− 1. ► We use the 3-phase 3-layer advection-diffusion analytical model to study WRF. ► Upper safety limit for radon source term (ECRa) in building materials is 10 Bq·kg− 1. ► Temperature sensitivity (TS) of WRF is studied using TS of ECRa and Henry constant.