The state of energy efficiency: IECC and the building enclosure

by Craig A. Hargrove, AIA, LEED AP

All images courtesy Hoffmann Architects
All images courtesy Hoffmann Architects

On 24 February, 2017, the New York Times ran an article regarding the eventual de-commissioning of the Indian Point nuclear power plant just north of New York City. According to the article, the governor intends to close the plant by 2021. This raises the question: How does New York State intend to replace the energy the plant created so they can still meet power demands?

As it turns out, they do not; not entirely. The article goes on to cite a report that determined New York’s best option is not finding alternative sources of power, but to follow states like Massachusetts and Rhode Island in enacting programs to reduce energy use.

New York is not alone in applying this calculus to energy policy, and the cumulative effect such decisions have on the built environment is significant. In 2010, the required insulative value for a new, low-sloped roof on a commercial building in climate zone 4 (the region that includes New York City) was R-20. Today, the 2018 International Energy Conservation Code (IECC) requires that same roof to have a value of R-30—a 50 percent increase. For windows, the change has been even more dramatic. In 2010, new fixed windows needed an R-1.82; today it is R-2.63—a 45 percent increase. Further, while similar values for exterior walls have remained largely the same, the method of assessing performance has changed greatly.

The 2018 IECC is the latest in a line of increasingly stringent regulatory requirements. While it is not necessarily a response to, these regulations certainly support a shift in policy being adopted by states like New York that seek to meet energy needs in part by reducing usage.

Today, the path to energy code compliance can be nuanced and complicated, requiring knowledge not just of standards and materials, but a basic understanding of scientific concepts like the laws of thermo- and fluid-dynamics. Stricter requirements now bring designers into potential conflict with competing codes on issues like combustibility and structural stability. It is, of course, unlikely this trend will ever reverse itself. Instead, the requirements for energy performance will simply continue to become more stringent and paths to compliance will be more complicated. With all of this in mind, an overview of the 2018 IECC and the science behind it might be helpful. To simplify things, the discussion in this article will be limited to commercial buildings.

An example of high-efficiency detailing, where a thermal break is provided at point transmittances, such as metal-to-metal connections.
An example of high-efficiency detailing, where a thermal break is provided at point transmittances, such as metal-to-metal connections.

Since its introduction in 2000, some version of IECC has been adopted in 48 states, the District of Columbia, and the U.S. Virgin Islands. The code incorporates the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1-2016, Energy Standard for Buildings Except Low-Rise Residential Buildings, by reference. While IECC incorporates approximately 87 outside publications by reference, these two standards (IECC and ASHRAE 90-1-2016) create the essential framework for establishing and demonstrating compliance with the mandated energy performance requirements of the building enclosure. During this discussion, unless otherwise stated, ‘code’ refers to the combined requirements of IECC and ASHRAE 90.1.


To understand the code, it is important to grasp that a path to compliance is entirely dictated by geography. Different locations require different strategies to achieve energy efficiency, and the first question to ask is: Is the project in a ‘heating’ or ‘cooling’ climate? The terms mean exactly what they might seem—in a heating climate there are more annual ‘heating degree days’ than ‘cooling degree days,’ and vice versa. While the code has specific definitions for these conditions, simply stated, a heating climate is one in which more days are spent heating the building than cooling it. For example, Boston is in a heating climate, while Miami is in a cooling zone.

ASHRAE 90.1 further divides the continental United States into seven climate zones that can broadly be defined as varying degrees of the following conditions:

  • moist heating climate;
  • dry heating climate;
  • moist cooling climate; and
  • dry cooling climate.

So, in general, the code establishes requirements in a region based on two criteria: temperature and moisture. The control of these two conditions is essential for thermal comfort and energy efficiency.

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