The engineers are going to base everything they do structurally the code book. This means when they stamp a drawing it meets minimum code requirements, and you can feel assured the building inspector is going to go off of the engineered plans or drawings when they are verifying the IRC requirements have been met. The engineer has to understand the calculations used in span charts and other charts in the IRC to make sure these calculations are input properly on to the pans. You will use the engineered drawings as the blueprint for how to build or remodel.