Related Links: ASHRAE Illuminating Engineering Society of North America 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