Existing buildings have a unique story to tell, and we as designers and engineers must tune our design process to "hear" how our buildings actually perform. On-site monitoring of dynamic environmental conditions provides empirical evidence for building performance, which adds granularity to energy modeling practices and empowers the design team to effectively analyze unique envelope characteristics. In this session, case studies of low-rise masonry renovation projects will provide examples of how envelope monitoring supported design decisions and helped achieve sustainability goals pertaining to energy use, operational efficiency, economic viability, and longevity.