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USGNN Original Story"Stretch" Energy Code in Massachusetts Could Mean More High-Performance Glazing Installations
July 21, 2009

A recently adopted code change proposal by the Commonwealth of Massachusetts could help spur increased use of high-performance glass and window systems in both commercial and residential applications. Appendix 120.AA, known as the "stretch" code, is an optional appendix to the Massachusetts Building Code 780 CMR that will be applied by August 1, 2009. The stretch code is similarly based on the IECC 2009 energy code, which will become the base energy code in 2010, but with approximately 20 percent greater building efficiency requirements, and a move toward third-party testing and rating of building energy performance.

The stretch code applies a performance-based code to commercial buildings, with a prescriptive code option for small and medium-sized buildings (5,000 to 100,000 square feet). Buildings smaller than 5,000 square feet, as well as building renovations and "specialty" buildings such as super markets, warehouses and laboratories that are fewer than 40,000 square feet, are exempt. The prescriptive code option is based on Chapter 5 of the 2009 International Energy Conservation Code and adds efficiency improvements to a number of areas, including the building envelope, as well as an option for on-site renewable energy, such as solar photovoltaics.

New residential buildings three stories or fewer will be required to meet an energy performance standard using the Home Energy Rating System3 (HERS). This index scores a home on a scale where 0 is a zero-net-energy home, and 100 is a code-compliant new home (currently based on the IECC 2006 code). The stretch code requires a HERS index of 65 or less for new homes of 3,000 square feet or more and 70 or less for new homes below 3,000 square feet (including multi-family units in buildings of three stories or fewer). A HERS index of 65 means that the home is estimated to use 65 percent as much energy as the same home built to the 2006 energy code, or a 35 percent annual energy savings.

Under Section 502 - Building Envelope Requirements, the appendix sets a U-factor of 0.42 for metal framing with or without a thermal break (curtainwall/storefront); the solar heat gain coefficient for all building envelope fenestration products is set at .40. For skylights, though, the limit is set at 3 percent of the roof area, but can be expanded to 5 percent of the roof area in conjunction with automatic daylighting controls.

In addition, the appendix says curtainwall, storefront glazing and commercial-glazed swinging entrance doors and revolving doors must be tested for air leakage at a pressure of at least 1.57 pounds per square foot in accordance with ASTM E 283. For curtainwall and storefront glazing the maximum air leakage rate is 0.06 cubic foot per minute per square foot (cfm/ft2) of the fenestration area. For commercial glazed swinging entrance doors and revolving doors, the maximum air leakage rate is 1.00 cfm/ft2 of the door area when tested in accordance with ASTM E 283.

In addition, the air leakage of window, skylight and door assemblies will be set in accordance to AAMA/WDMA/CSA 101/I.S.2/A440 or NFRC 400 by an accredited, independent laboratory, and labeled and certified by the manufacturer. Window and skylight air leakage cannot exceed 0.2 cfm/ft2 at 1.57 pounds per square foot, or 0.3 cfm/ft2 at 6.24 pounds per square foot. Door assembly air leakage must not exceed 0.3 cfm/ft2 for all other products at 1.57 pounds per square foot.

CLICK HERE to read the code change proposal.

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