When you plan a retrofit for air tightness and insulation to the exterior, considerations for dew point and drying potential must be part of designing the most appropriate layering.
Two important points to remember:
In Canada's 2020 National Building Code - Division B, Section 9.25.5.2, there are instructions for how a building envelope assembly should treat low permeance materials - these are layers that don't allow air or moisture to pass through. The following diagrams from the 2020 NBC Illustrated User's Guide show the requirements for assemblies with low permeance layers in different locations: