Energy Efficient Building Codes: Version Matters

Newer Codes Reflect Advances in Energy Efficiency

Original research by Ryan Meres, Institute for Market Transformation


Advances in technology, design, and construction continuously improve the potential energy efficiency of buildings. In response, energy efficiency building codes are continuously updated to reflect new best practices and off-the-shelf technologies, setting more rigorous standards that propel building energy efficiency forward.

Building codes cover all aspects of building construction, with specific standards focused on energy efficiency. States maintain their own building codes, which typically reference one of two sets of code standards: the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) code and/or the International Code Council (ICC) (note that whereas ASHRAE’s codes are specifically focused on building energy, ICC codes cover all aspects of construction). The respective energy efficiency standards are ASHRAE 90.1 and the International Energy Conservation Code (IECC). The process for adopting these codes can differ widely from state to state, as evidenced by comparing New Jersey’s and Pennsylvania’s processes.


The Institute for Market Transformation and CBEI compared the energy efficiency criteria defined by two versions of the ASHRAE 90.1 standard – 90.1-2001 and 90.1-2010. The results are telling. The Building Code Assistance Program estimates that a building constructed to the 2010 standard would save 41% in energy use compared to the same building built to the 2001 code [1]. Applied to a 50,000 sq. ft. building, this would mean an annual energy savings of $57,600 using energy costs from Econsult’s retrofit market analysis report [2].

The table below summarizes some of the differences between the two versions of the code. For example, the 2001 and 2010 codes treat vertical fenestration (window) requirements very differently, as illustrated by U-value and Solar Heat Gain Coefficient (SHGC) requirements: the 2001 code stipulates U-values and SHGC depending on how much of the exterior wall is covered by windows as well on whether the fenestration is fixed or operable, whereas the 2010 standard prescribes the same standards for up to 40% exterior wall glazing (beyond 40% glazing requires performance-based compliance with the energy code), but does take into account the window material (i.e., metal frame, non-metal frame, etc.).

Interior lighting controls have advanced significantly between 2001 and 2010, something that is reflected in the ASHRAE standards from those years. While the 2001 standard required an automatic lighting shutoff for spaces greater than 5,000 square feet, the 2010 standard requires, in addition, automatic controls for areas with daylighting (controlled natural lighting of interior spaces) and functional testing to ensure proper working order for all lighting control devices and systems.

Exterior lighting control standards have also grown more rigorous. The 2001 standard simply required that the building façade be lit. The 2010 standard goes further, additionally requiring automatic controls for exterior lighting that reduce the lighting power by 30% during non-operating hours and that shut off the lighting entirely when sufficient daylight is available.


[1] Petermann, N. (2012, April 30). Bcap codes savings estimator primer. Retrieved from

[2] Econsult Corporation. (2011, October). The market for commercial property energy retrofits in the Philadelphia region. Retrieved from