The widespread availability of computerized hygrothermal analysis has given designers a powerful tool to assess the impact of changes to wall assemblies, one of the most common being the addition of insulation to existing walls. When evaluating these changes in solid brick masonry construction, accurate representation of the properties of the brick is critical to providing meaningful results. Given the extreme variability in brick properties, relying on "standard" properties from program databases and similar sources will rarely yield accurate results. This paper discusses the issues associated with insulating solid brick masonry walls, methods for testing and evaluating the material properties and performance of brick, and comparison/interpretation of results using both "default" and physically tested properties for the masonry.