Cross-laminated timber (CLT) is a prefabricated mass timber building material that has the potential to expand the wood building market. While considerable research has been directed at CLT building system structural and fire behavior, little is known about the moisture conditions in CLT buildings during the construction process and in service. To better understand these conditions, USDA Forest Service researchers at the Forest Products Laboratory in Madison, Wisc., have teamed up with researchers from the Colorado School of Mines and installed wireless sensors in mass timber buildings located in three different U.S. climates. In addition to long-term monitoring, the research team has measured the relevant material properties of CLT and developed wetting and drying experiments in the laboratory. These on-site and laboratory measurements have led to more accurate computer simulations that can predict moisture conditions in mass timber buildings. These results will improve the confidence of architects and engineers in designing mass timber buildings for moisture durability.