The IECC is the model code and ASHRAE 90.1 is the standard upon which the model code is based. Individual states and municipalities may modify the model IECC code by amendments. We reference the adopted code with amendments (if applicable) for each location in the United States. Thus, we reference both the model code and the ASHRAE Standard so that users can look up the relevant standard.
Our inputs are based on engineering best practices for that location and code and maybe slightly different than the model IECC code. The goal is to create a realistic model. The main differences between the IECC and ASHRAE 90.1 are inputs like Lighting Power Density (LPD), Equipment Power Density (EPD), and sometimes equipment efficiencies. Engineers may want to modify these inputs based on their experience.
For more details about energy codes within cove.tool, please reference this article: Performance and Prescriptive Path for Building Code Compliance.