The updated energy standard for buildings includes big revisions to building envelope, lighting and mechanical appliance requirements. The changes make the 2013 update 40% to 50% more stringent than the 2004 version, according to ASHRAE, which recently published the standard.

ANSI/ASHRAE/IES Standard 90.1-2013, Energy Standard for Buildings Except Low-Rise Residential Buildings, incorporates 110 addenda that reflect changes to the 2010 energy standard.

The prescriptive window-to-wall ratio remains 40%, but stricter fenestration provisions require double-glazed windows in many climates and establish a minimum visible-transmittance/solar-heat-gain-coefficient ratio to allow daylighting with minimal solar gain.

Minimum efficiencies are increased for chillers, heat pumps and air conditioners and included for fans for the first time.

In lighting, "the focus in the 2013 standard was not just on lowering interior lighting power densities but on finding ways to achieve savings by adding more controls and daylighting requirements," says Rita Harrold, director of technology for the Illuminating Engineering Society of North America (IES), which codeveloped the standard. A result is more stringent space-by-space lighting-power-density limits and thresholds for top lighting.

Standard 90.1 acts as a benchmark for commercial building energy codes and can apply to all but low-rise residential buildings. It will likely take a few years to become widely used: ASHRAE 90.1-2010 is referenced in the LEED version 4 green-building rating system, which comes out next month, and 90.1-2007 and 90.1-2004 are still commonly used in local codes. Only eight states use the 2010 version; 34 states use the 2007 version. ASHRAE expects to see some 2013 update adoptions in 2016.