Each of the 12 technical chapters (3 through 14) begins with an overview followed by each subsystem. For the building envelope, subsections include fenestration, insulation, infiltration, roofing products, and so forth. For HVAC, the subsections include heating equipment, cooling equipment, and ducts. Mandatory requirements and prescriptive requirements are described in each subsection or component. The prescriptive requirements establish the stringency of the Energy Code because they are the basis of the energy budget when the performance compliance method is used.