The rapid development of LoRa and LoRaWAN received a wide interest in research in order to understand the performance of this technologies for various Internet of Things (IoT) applications. In this article, we propose an IoT system for smart buildings based on LoRa and LoRaWAN. The main aim of this system is monitoring the moisture of wood in buildings; specifically, in cultural heritage buildings. Monitoring uses wireless sensor nodes that are digitally controlled and low power. The wireless sensor node includes a moisture sensor that relies on a novel resistance measurement method which is developed and tested, including a new printed circuit board (PCB). The sensor comprises an LoRa communication module in order to be used as the end node of the proposed system. To complete the monitoring system, a cloud-based application was developed to provide remote visualization and control for all LoRa sensor nodes in a building. The proposed system is scalable and represents a practical solution for the early detection of wood moisture due to heavy rain, leaks, etc. The path loss is evaluated, showing that the proposed LoRa system can be applied for preservation of heritage buildings despite the attenuation of thick walls and complex architectural structures.