The objective of this paper is to demonstrate the importance building envelope consultants have in implementing a methodology of investigation tailored to the type of building envelope and problem under review. This includes the use of diagnostic tools needed to uncover both evident and less apparent failure mechanisms. The present-day environment in southern Québec has been impacted by climate change that has exacerbated to varying degrees the problems encountered in many of our buildings. Climatic models point to several changes including increased precipitation (rain)during winter months, increased occurrences of freeze–thaw cycling, and an increased frequency in the intensity and duration of climatic events. The influence of such changes on our building inventory coupled with poor design, and poor workmanship make it imperative that a more extensive application of diagnostic tools be used to better define the various failure mechanisms that contribute to the observed deficiencies. We will consider examples of buildings that have been subjected to extensive study using various diagnostic tools.Two practical case studies shall be presented of buildings in eastern Canada. The first case reviews attic spaces of a government building with limited access, which required the use of various often rarely used diagnostic tools to explain the sources of water infiltration. The second case reviews a masonry clad institutional building where site conditions, including exploratory openings, and on-site and laboratory testing, led to the identification of various mechanisms of failure that contributed to the observed deficiencies.