An experimental apparatus was built and operated for the measurement of moisture permeability of building materials. The data are for use in resolution of problems associated with moisture buildup in porous building materials. The apparatus is capable of maintaining simultaneous humidity and temperature differences across a test specimen. In contrast with existing experimental methods, the relative humidity on either side of the specimen is controlled without the use of quiescent saturated salt solutions. Forced-air convection at the surface of the specimen is used, resulting in uniform spatial conditions and faster results. Data are obtained for fiberboard sheathing at various temperature and humidity setpoints. The apparatus consists of two environmental chambers between which a wood-based test specimen is sealed. An external forced-air conditioning system using distilled water and molecular sieve desiccant humidifies or dries the chamber air as needed. The moisture transfer rate across the specimen is determined gravimetrically: the desiccant column is weighed to measure its change in mass as a result of moisture diffusion across the specimen. The apparatus is capable of maintaining relative humidities over a range of 5 to 65 percent RH, with a temperature difference across the specimen of up to 20°C. Furthermore, the apparatus is capable of automated relative humidity and temperature control to within ±0.5 percent RH and ±0.5°C of the setpoints, respectively. Test results for fiberboard sheathing subjected to a range of humidity and temperature conditions are presented. Results are compared with the limited data from the literature. Recommendations for improvement of the data measurement methods are included. / Master of Science

An experimental apparatus and test procedure to measure the sorption isotherm of moisture in porous building materials was developed and tested for its reliability and accuracy. The apparatus shows excellent potential for determining reliable moisture storage property data. The data are used in heat and moisture transport models. The apparatus consists of a small test chamber, with an external forced-air temperature and humidity conditioning system. The conditioning system supplies moist air to the test chamber at 20°C dry-bulb temperature over a range of 0.4 to 85 per cent relative humidity. The new system circumvents problems associated with the use of saturated salt-in-water solutions. Moisture content is determined gravimetrically without removing specimens from their conditioned environment. The mass is monitored in situ such that external ambient conditions have no effect on the data. The control of test chamber relative humidity and dry-bulb temperature is automated. Test results consisting of sorption isotherms and scanning curves for sugar pine, southern pine, and an exterior grade plywood are presented. The maximum uncertainty in moisture content measurement is 0.023 kg/kg-dry mass at 85 per cent RH. Results are compared to data from the literature. The study shows a need for a standard test method for measuring sorption isotherms. Minimum recommendations for such a standard test method are included. A comparison of scanning data to an analytical model from the literature show that further investigation of scanning is needed. The present method is well suited for such a study. / Master of Science