Ken Nittler, P.E., of NFRC-approved simulation laboratory WESTLab, surveyed energy code development. Primary national model codes are the IECC for residential construction and the IECC and ASHRAE 90.1 for non-residential construction. The most recent (2015) version of the IECC contains separate, stand-alone residential and commercial energy codes. The 2015 IRC actually duplicates the IECC residential code in its Chapter 11.

As of 2014, ASHRAE 90.1-2013 has been approved by DOE as an alternative compliance option for high-rise residential and non-residential. Jurisdictions typically adopt model codes, occasionally with local amendments – although some states, notably California, promulgate their own unique codes. State-by-state adoption status can be viewed online here or here.

The IECC has featured the same basic approach to U-factor and Solar Heat Coefficient (SHGC) since the mid-1990s. Both ratings must be determined per NFRC 100 or NFRC-200 or obtained from limited default tables. The latter often assign unfavorable values, as they give no credit for Low-E glazing or gas-filled insulating glass units (IGUs). Since 2006, permissible residential U-factors and SHGCs have been dropping in subsequent code editions, lowering 2012 by some 30 to 40 percent – particularly in warm southern climate zones.

Meanwhile, commercial requirements have evolved to be substantially simplified and material neutral. New prescriptive vertical fenestration U-factors, for both new construction and replacement, are assigned using three categories: fixed, operable and entrance door. To simplify commercial SHGC requirements, in the 2015 edition a 0.25 SHGC will comply in all localities and at all orientations; 0.40 will comply in climate zone 4 and 0.45 will be acceptable in climate zones 7 and 8. Skylights are addressed separately.

Typical fenestration-related compliance problem areas were reported as involving fenestration air leakage, proper performance labeling and U-factors of opaque doors.

Nittler also reviewed the non-residential NFRC Component Modeling Approach (CMA), in which frame and spacer manufacturers obtain simulations and testing, placing results in the Component Modeling Approach (CMA) Software Tool (CMAST). The specifying authority, often the glazing contractor, specifies the product to be used on a specific project and, referring to the database, an Accredited Calculation Entity (ACE) prepares certified label certificates. Nittler reviewed the basic function of the software using various screen shots from CMAST.

A continuing problem area in the application of CMA lies in the treatment of products used in a project, which are not included in the specified sizes and are not NFRC certified, leading to confusion over acceptance of different window configurations. Noting that some buildings could have dozens of actual products vs. just those specifically specified, Nittler explained that open questions include whether actual size means actual configuration and how to address windows with specialized corners, shapes or curves.

(See “Evolution of the NFRC CMA Programs” article for more on the status of CMA).