Equilibrium moisture content data are presented as a function of relative humidity for common building materials: plywood, oriented strand board, vinyl covered gypsum board, plain gypsum board, extruded polystyrene insulation, and insulation board. The measurements were made using a new technique where the samples are suspended inside a chamber containing saturated salt-in-water solutions that maintained various relative humidity levels ranging from 11.3% to 97.6% while at a constant temperature of 21°C (70°F). Isothermal and non-isothermal moisture flux data for oriented strand board and extruded polystyrene insulation are also provided. Isothermal measurements carried out at 24°C (75°F) and 7°C (45°F) indicated that the average temperature does not significantly affect the permeability for the materials. The moisture permeability is given as a function of average relative humidity for each material. The measured moisture flux under isothermal and non-isothermal conditions is compared to the theoretical values predicted by two recent models which predict combined heat and mass transfer in hygroscopic materials. The isothermal data agree well with the model predictions. There is less agreement with the non-isothermal data, indicating a need for further model development.