Decoding the green construction codes

Engineers should understand the difference between IgCC and ASHRAE 189.1 energy compliance code provisions.


Voluntary green building rating systems such as the U.S. Green Building Council’s LEED program have had significant impacts on the building industry. Some jurisdictions have attempted to make LEED certification a requirement for new buildings but have encountered a need for a code compliance path to document performance. The USGBC assisted in the development of both the ICC International Green Construction Code (IgCC) and ASHRAE 189.1, Standard for the Design of High-Performance, Green Buildings Except Low-Rise Residential Buildings, to fill this void.

Both codes focus on the five categories of sustainability addressed in LEED New Construction: Site Sustainability, Water Use Efficiency, Energy Efficiency, Indoor Environmental Quality, and Materials and Resources. Furthermore, both codes include an additional section regarding Operation and Maintenance.

The IgCC and Standard 189.1 are not guides or ratings systems. They are written in mandatory code language and intended for adoption and enforcement by the local and state level. In earlier versions of IgCC, ASHRAE 189.1 was a “jurisdictional compliance option,” meaning the local authority must choose between 189.1 and IgCC. With IgCC 2012, a building may now choose to comply with its standard requirements or those of 189.1.

Several major differences within the energy efficiency sections differentiate the two codes. With all energy units converted to Btus, IgCC is based on source energy use, while ASHRAE 189.1 is based on site energy cost. Just as energy cost and energy consumption are two completely different metrics, so are site and source energy. Different energy-saving measures will apply to a project, depending whether site energy cost or source energy use is the applicable metric. A model executed according to the calculations of one code cannot easily be compared to the other. A section of the IgCC also requires that the person performing the energy simulation be a professional engineer or architect in the state where the project is being constructed; ASHRAE 189.1 currently does not have a similar requirement.

Both codes contain comparable requirement categories in other sections, but with notable differences. The following table summarizes the key differences between ASHRAE 189.1 and IgCC 2012:

The IgCC has more detailed requirements for building energy metering and demand response, while ASHRAE 189.1 provides more detailed sections on fan power and demand controlled ventilation. If a project requires compliance with IgCC, there is always the option of using either IgCC or ASHRAE 189.1. For projects pursuing LEED certification, the energy model will compare energy cost. Overall, using ASHRAE 189.1 as a compliance path can minimize modeling time and increase cost-based savings.


Bridgette Baugher is an energy engineer with Southland Industries. Her career focus is on improving energy efficiency in new and existing buildings through the use of analysis and auditing tools. She served on the Center for the Built Environment’s Livable Buildings Jury in 2009 and 2010.   

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