This paper describes a cloud based architecture which has been designed for the monitoring of Cultural Heritage buildings. The architecture has been deployed in museums and basements proving its capabilities. The solution is composed of small sensing nodes with volume lower than 8 cm3 and dimensions of 2.5 cm× 1.5 cm which are capable of acquiring temperature and relative humidity for interval in excess of one year. The nodes are battery operated and communicate wireless to small Arduino-based concentrators connected to the internet and to a cloud storage. Data from all the nodes are made available to on the curator’s smart phones in real time so that the entire building can be monitored from everywhere. The nodes have the capability of locally storing all the measurements for quality assurance and if either the internet connection is not available, or the power supply is missing, the proposed system has the possibility of manually uploading data to the cloud after having transferred them from the nodes to a battery operated PC.