Residential energy codes have evolved rapidly over the last two decades. The origin of many of our current energy codes can be traced back to the Model Energy Code (MEC), which was first introduced in 1992. The MEC eventually evolved into the International Energy Conservation Code (IECC).
In jurisdictions that have adopted the International family of codes, residential builders can usually use the IECC to fulfill energy code requirements. But most home builders choose instead to follow the simpler energy requirements found in the International Residential Code (IRC). Confusingly, IRC energy requirements are similar but not always identical to requirements found in the IECC.
The 2004 Supplement to the IECC included radical revisions to the existing energy code. These revisions were designed to simplify the code, in hopes that a simpler code would lead to better compliance by builders and easier enforcement by building officials. These 2004 revisions were designed to be “stringency neutral” — that is, to result in homes that were neither more nor less efficient than homes built to earlier versions of the code.
The 2004 revisions were fully implemented in the 2006 versions of the IECC and IRC. The latest version of the codes — the 2009 IECC and IRC — include revisions designed to increase energy code stringency. (For more information on changes adopted into the 2009 codes, see Exceeding the Energy Code.)
The window-to-wall ratio
In pre-2004 versions of the IECC, builders were required to calculate the ratio between a home’s window area and its solid-wall area; this ratio was usually called the window-to-wall ratio (WWR). No matter which compliance path a builder chose — the prescriptive path, the component trade-off path, or the performance path — there was no escaping the requirement to calculate the WWR. Some builders grumbled at the need to make this calculation.
Homes with a low WWR usually use less…