Adhesive mounting of photovoltaic (PV) modules on residential roofs can significantly reduce the installed cost. The potential for undesirable moisture buildup under the module, however, may reduce shingle life and degrade the underlying roof elements. High moisture levels in roof elements may also adversely affect the energy performance of the building. This study investigates whether an adhesively mounted PV system causes a preferential moisture buildup under the module on an asphalt shingle roof. Lightweight PV modules were adhesively mounted on half of the roof of an instrumented test hut located in Boston, MA. Moisture pin sensors, installed in various locations of the roof deck, determined the moisture content (MC) of the wood in the roof assembly. The MC is found to follow a seasonal pattern: lower values (7–11 %) during the summer and higher values (11–15 %) during the winter. MC measurements during the winter and summer seasons showed no adverse impact of the adhesive-mounted rooftop PVs on the hygrothermal behavior of the underlying roof deck element over the 1-year measurement period.