CODE UPDATE

Energy Conscious
An Update on Glass-Related Energy Codes
by Thomas D. Culp, Ph.D.

When it comes to glass-related codes, the two most recent standards covering the energy performance of commercial buildings are ASHRAE 90.1-2007 and the 2009 IECC. Although there have been significant changes in the glazing requirements from earlier versions (between ASHRAE 90.1-2004 and ASHRAE 90.1-2007, and between the 2003 IECC and 2006 IECC), the most recent versions are very consistent with each other.  

For vertical glazing, the 2009 IECC made only small changes to U-factors and solar heat gain coefficient (SHGC) in zones 7-8 (including Alaska, northern Minnesota and northern Wisconsin) to bring the requirement more in line with ASHRAE 90.1-2007 (see table below).

Skylights
The largest change in the 2009 IECC was for skylights. The 2006 IECC contained separate requirements for plastic and glass skylights, but the 2009 IECC combined these into one category, choosing more stringent U factor and SHGC values. This may present difficulty for some types of skylights, as low-E coatings are not currently available on plastic dome skylights. In many cases, trade-offs in the performance path will have to be used to satisfy the code requirements.

In reality, the largest change architects may see this year is increased adoption and enforcement of these standards, due to the renewed focus on energy efficiency, as well as funding for high-performance green federal buildings and state incentives in the American Recovery and Reinvestment Act of 2009.

Energy Star®
In other matters, the U.S. Department of Energy announced revised criteria for its Energy Star program for windows, doors and skylights. This included an important clarification that the Energy Star program is only for products used in low-rise residential buildings that are three stories or less; it does not apply to high-rise residential buildings or commercial buildings. Many architects have made the mistake of specifying Energy Star windows in commercial or high-rise residential projects, without understanding that the Energy Star program was developed only for residential products, and that the performance attributes of commercial windows are very different due to structural and durability considerations.

Changes in the 2009 IECC Commercial Glazing Requirements Vertical Fenestration

Vertical Fenestration (40% maximum of above-grade wall)

U-factor

Framing materials other than metal with or without metal reinforcement of cladding

Metal framing with or without thermal break

SHGC-all frame types

Source: ICC/IEC

NR = No requirement.
PF = Projection factor (see Section 502.3.2.)
a. All others includes operable windows, fixed windows, and nonentrance doors

Future Revisions
There are also many significant and important changes that will be coming in the next edition of the codes. ASHRAE is working under profound pressure to increase the stringency of the 2010 version of ASHRAE 90.1 by 30 percent. Several significant proposals are already out for public review, including:
• Complete revision of the prescriptive U-factor and SHGC requirements for commercial glazing;
• Mandatory use of skylights and lighting controls in large open spaces, such as warehouses and big box retail, to maximize daylighting energy savings; 
• Updated air leakage requirements for fenestration;
• Requirements for a continuous air barrier, which will require attention at the interface between fenestration and walls; and
• Requirements to use more glazing area on the south side of the building than on the west and east sides.
The same ideas will likely also be discussed for the 2012 IECC. AG

Thomas D. Culp, Ph.D. is an industry consultant with Birch Point Consulting LLC in La Crosse, Wis. Dr. Culp’s opinions are solely his own and not necessarily those of this magazine.

Architects' Guide to Glass & Metal
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