The State of Oregon has established standards for energy efficiency in commercial buildings, including for windows.  In summary, windows (frame and glass assemblies) must have a u-value less than 0.50 and a shading coefficient less than 0.57.  What this means is that you must have a tinted outboard pane in an insulating glass unit with standard low-e, or a high-performance low-e if you utilize clear glass.

For more detail, including a list of configurations that meet the code, Click here for summary of Commercial Window Performance Standards