Codes and Standards
The code landscape and what each document governs
Codes questions test scope, not memorized numbers. ASHRAE Standard 90.1 governs energy efficiency in commercial buildings and residential buildings more than three stories above grade. The IECC splits into a residential (R) chapter and a commercial (C) chapter, and it accepts 90.1 as an alternate path for commercial work. Know the companions: 62.1 is ventilation (not energy), 55 is thermal comfort, 100 is energy efficiency in existing buildings, 105 and Guideline 0/Standard 202 cover commissioning, 211 defines audit levels, and ISO 50001 is an energy management system standard, not a design code. Federal equipment minimum efficiencies under EPAct preempt weaker state rules.
Compliance paths and the traps they create
90.1 permits a prescriptive path (envelope, lighting power density, HVAC efficiency tables) or a performance path using Appendix G, the Performance Rating Method. Appendix G compares a proposed design against a baseline built from the prescriptive tables and produces a percentage improvement in energy cost, not energy use. Traps: treating Appendix G as a comparison to the existing building; confusing lighting power density (W/ft2, which the code regulates) with illuminance (foot-candles, which it does not); citing Standard 62.1 as an energy requirement; and applying a new-construction code to an existing-building alteration when Standard 100 governs.
Rule of thumb
Three stories or fewer above grade means residential scope; four or more means commercial scope. A four-story hotel follows 90.1 or IECC-Commercial; a three-story apartment building follows IECC-Residential.