Typically, the adoption and enforcement of a new edition of the model codes doesn’t start to take hold until at least a year after the codes are published. With regard to the 2012 International Codes there seems to have been some delay, but more jurisdictions are now enforcing them: According to the ICC website, as of late January 2014, the 2012 International Building Code was being enforced in 17 states, the 2012 International Residential Code in 13 states and the 2012 International Energy Conservation Code in seven states.
Therefore, it seems appropriate at this time to review some of the more significant new requirements of the 2012 I-codes for fenestration.
Design Wind Speed Model
Perhaps the most significant change from the 2009 IBC to the 2012 IBC is the updated reference from ASCE 7-05 to ASCE 7-10, which changes the design wind speed model from one based on allowable stress design to one based on strength design. The 2012 IBC also introduced separate design wind speed maps.
The new model―and the corresponding design wind speed maps―result in higher design wind pressures. But don’t compare these higher design wind pressures to the Design Pressure or Performance Grade ratings fenestration products receive under AAMA/WDMA/CSA 101/I.S.2/A440. Those DP ratings are based upon allowable stress design and not strength design. For a direct comparison to a labeled window’s PG rating, multiply the higher strength design wind pressure by 0.6.
The 2012 IRC doesn’t use the new design wind speed model. Therefore, the design wind pressures determined in accordance with the 2012 IRC can be compared directly to the DP rating received under AAMA/WDMA/CSA 101/I.S.2/A440.
Table 1 indicates on which design wind speed model each of the indicated documents are based.
For more information, read AAMA, WDMA and DASMA’s joint technical paper regarding the application of the new design wind speed provisions for fenestration products labeled in accordance with AAMA/WDMA/CSA 101/I.S.2/A440.
Window Opening Control Devices
Since 2006, there have been several changes to sill height requirements and window openings. Table 2 outlines those changes. One addition to the 2012 IBC is the exception to the minimum window sill height requirement for windows equipped with Window Opening Control Devices. Both the 2012 IBC and 2012 IRC refer to the 2011 edition of ASTM F2090 for the criteria for these devices.
The minimum sill height for operable windows in apartment buildings also was raised from 24 inches to 36 inches in the 2012 IBC. The minimum sill height remains at 24 inches in the 2012 IRC.
The 2012 IRC permits four possible methods of window installation. Windows are to be installed in accordance with fenestration manufacturers’ installation instructions, when provided. For wall configurations not addressed in those instructions, pan flashing, a method specified by a registered design professional, or a method that has been otherwise approved by the code official, is to be used.
Prescriptive U-factors and SHGCs
There are slight changes in maximum U-factor and Solar Heat Gain Coefficient for residential fenestration under the prescriptive provisions of the 2012 IECC in comparison with the 2009 IECC. These are most significant in the southern climate zones.
Unlike the 2009 International Codes, the energy provisions of the 2012 IRC are now identical to those of the 2012 IECC for low-rise residential construction. The primary impact of this on fenestration is that now there is only one set of fenestration maximum U-factors and SHGC for compliance under the prescriptive provisions of the 2012 IECC and 2012 IRC. As a general rule, this has resulted in more stringent provisions for residential fenestration overall.
Another change in the 2012 IECC is that separate SHGCs have now been established for skylights. Although the 2009 IECC had separate U-factors for skylights and vertical glazing, they were both subject to the same maximum SHGC. This has changed in the 2012 IECC.
Figure 1 shows the maximum prescriptive U-factor and SHGC for vertical glazing under the prescriptive provisions of the 2012 IECC. Figure 2 shows the maximum prescriptive U-factor and SHGC for skylights under the prescriptive provisions of the 2012 IECC.
The 2012 IECC and the 2012 IRC continue to cap the prescriptive maximum U-factor and SHGC permitted to be traded off when using performance-based design. Under both codes, the maximum area-weighted average U-factor permitted for vertical fenestration is 0.48 in the transitional climate zone shown in dark blue in Figure 1 and 0.40 in the northern climate zones shown in bright pink in Figure 1.
For skylights, the maximum permitted area-weighted average U-factor is 0.75 in the climate zones shown in green and blue in Figure 2, even when performance-based design is used. Also, even when performance-based design is used, both codes restrict the area-weighted average maximum fenestration SHGC in the cooling dominated zones shown in red, yellow and light blue in Figure 1 to 0.50.