Basement radon entry and stack driven moisture infiltration reduced by active soil depressurization

Abstract

This case study presents measurements of radon and moisture infiltration from soil gases into the basement of an unoccupied research house in Madison, Wisconsin, over two full years. The basement floor and exterior walls were constructed with preservative-treated lumber and plywood. In addition to continuous radon monitoring, measurements included building air tightness, indoor–outdoor pressure difference, indoor and outdoor temperature and relative humidity, wood moisture content, and tracer gas decay. A single-zone air infiltration model was calibrated based on tracer gas measurements. Soil moisture infiltration was determined by mass conservation after accounting for all other moisture flows: humidification, air exchange, diffusion through the above-grade building envelope, sorption in hygroscopic materials, and moisture removal by air conditioning. A moisture balance methodology used in previous work was validated and improved here by including two time scales in the sorption modeling. Active soil depressurization was applied and shown to reduce both radon and soil moisture infiltration. The stack effect is shown to correlate well with soil moisture infiltration but does not fully explain radon entry.