Indoor radon surveying and remediation were implemented in a single-family home affected by high levels of indoor radon in the Celleno municipality (central Italy) with the aim of identifying the contribution of radon sources, evaluating the factors affecting radon entry into the building, and reducing radon risk. Average radon levels were relatively low at the ground floor (286 ± 202 Bq m⁻³) and first floor (167 ± 84 Bq m⁻³) in autumn when the temperature was still warm and the windows were open, but increased up to 2776 ± 1768 Bq m⁻³ and 970 ± 202 Bq m⁻³ in the first half of December, when the heating system was on and the windows were closed. The inner walls of the pilot room at the ground floor, semi buried on one side, were then treated with a waterproof product (a silane terminated polymer) and the average radon was halved (1475 ± 1092 Bq m⁻³) in the following month, which was still characterised by winter conditions. Radon entry in the room was identified and sealed with the same product, and a radon accumulation space behind a NE-SW oriented wall was naturally ventilated, reducing radon below the reference level in April with northerly winds conditions.

Indoor radon is the second cause of lung cancer. Mitigation strategies are based on (i) building protection with radon barrier materials, (ii) increasing home ventilation or (iii) room pressurization. A scale model room created with a porous ignimbrite rich in radon precursors was used as an analogue to test the indoor radon reduction ability of various radon barrier materials in a real room. The properties of these materials were tested with and without room pressurization by introducing outdoor air at different flow rates. The best materials reduced indoor radon up to 80% and, when the highest pressurization was applied, to 93%.

Indoor radon is one of the most significant contributors to lung cancer after smoking. Mitigation strategies based on protecting buildings with radon barrier materials, combined with home ventilation or room pressurization, are regularly used. A scale model room made from a porous ignimbrite rich in radon precursors was used as an analogue to test the efficiency of fifteen airtight membranes to reduce radon levels, also in combination with room pressurization. The results of these experiments were considered together with previous ones to propose the scale model room approach as a tool for rapidly evaluating the performance of specially designed radon barrier materials, and for radiation exposure assessment. Relative reduction of indoor radon (RIR) ranges from −20 to −94%. The most effective materials were FPO membrane, single-component silane-terminated polymer membranes and synthetic resins. The presence of additives likely modified the composition and structure of some products, improving their radon barrier capacity. The introduction of room pressurization further reduced radon levels in the model room where the membranes were applied. The overpressure necessary to reach RIRs of the order of 85–90% is very low for materials that powerfully stop radon even without ventilation, but necessarily higher for poorer membranes.

Indoor radon is classified as a carcinogen because it can lead to lung cancer. Some radon preventive strategies are related to building protection with radon barrier materials whose capacity to stop the gas depends on the diffusion coefficient, which can be calculated using different techniques. In this article, we propose a new experimental device, called TESTMAT, to measure the radon diffusion coefficient, using a weak radon source, to prevent radiation protection oversight. The device is small and made from PVC. The sample of the tested material is placed between the source and the receiver containers, as indicated by ISO/TS 11665-13 standard. Since a non-stationary radon diffusion occurs in the system, we developed a specific software, ENDORSE, to model radon activity concentrations in the receiver chamber and the diffusion through the material by applying the explicit finite difference method. The software utilizes Montecarlo simulation to determine the error associated with the diffusion coefficient. Different tests were performed to calibrate the system and assess the value and the evolution of background radon during the two-week measurement. When working with low-activity radon sources, this parameter cannot be neglected, particularly with the best performing membranes. An adequate sample holder was selected to guarantee a good airtightness, with a leakage constant of only 7 % of the radon decay constant. The minimum detection limits were calculated based on the material thickness and the source intensity. The system was finally tested with three commercially available waterproofing membranes and results compared with expected values, based on literature.

This study investigates how external insulation materials used for energy efficiency affect indoor radon accumulation, using a scale model room built with ignimbrite, a highly radon-emitting volcanic rock. Two insulation materials—mineral wool (open-cell, 98% porosity) and extruded polystyrene (XPS, closed-cell, >95%)—were applied to the outer walls of the model room. Their effects were tested in combination with three internal radon barriers (silane-terminated membrane, silicone sealant, bitumen membrane) and under varying ventilation rates (0.11 h⁻¹ and 0.44 h⁻¹). Radon concentrations were measured using calibrated detectors over five experimental phases. Without ventilation, XPS increased indoor radon by up to +351%, while mineral wool showed a milder effect (+26%). The silicone sealant reduced radon by up to 90%, outperforming other barriers. Ventilation significantly lowered radon levels, simulating the “flushing” effect of wind. The combination of impermeable insulation and lack of air exchange led to the highest radon accumulation. High-performance insulation can compromise indoor air quality by trapping radon, especially in buildings with high geogenic radon potential. Effective mitigation requires pairing insulation with high-performing radon barriers and adequate ventilation. These findings highlight the need to balance energy efficiency with indoor environmental safety.