2004 IECC (supplement to 2003 IECC)

Residential

Regulatory Requirements

The U-factor and solar heat gain coefficient (SHGC) of fenestration products shall be determined in accordance with National Fenestration Rating Council Standards NFRC 100 and NFRC 200 respectively by an accredited, independent laboratory, then labeled and certified by the manufacturer. Products not meeting these requirements shall be assigned product values based on defaults values. The default values typically do not give full credit for energy efficient performance.

Air leakage requirements are set at 0.3 cfm/sf for windows and sliding doors (cubic feet per minute per square foot of window area) and 0.5 cfm/sf for swinging doors. Fenestration systems must be tested in accordance with AAMA/WDMA 101/I.S.2.

Simplified Prescriptive Requirements

The IECC made signifcant changes to the 2003 IECC and published them as a supplement to the 2003 IECC.  Fenestration was directly affected by the changes.  The US Department of Energy was the primary force behind the changes.  Their goal was to simplifiy the 2003 IECC. 

The 2004 changes include:

• Dramatically simplified climatic zones (only 8 including humidity references)
• Maximum U factors & SHGC when using trade offs
• Simplified Component and Prescriptive fenestration compliance (see below)

The new prescriptive tables by climate zone is shown below:

(Table 402.1 in the 2004 IECC supplement)

Click here to see the corresponding climate map.

Total UA alternative

If the total building thermal envelope UA (sum of U-factor times assembly area) is less than or equal to the total UA resulting from using the U-factors in Table 402.1.2 (see below, multiplied by the same assembly area as in the proposed building), the building shall be considered in compliance with Table 402.1 (above). The UA calculation shall be done using a method consistent with the ASHRAE Handbook of Fundamentals and shall include the thermal bridging effects of framing materials. The SHGC requirements shall be met in addition to UA compliance.

(Table 402.1.2 in 2004 IECC supplement)

Simulated Performance Alternative

This method allows the designer to model the building using prescriptive method compliant components creating a "standard" design and an associated energy budget.  The designer then may model the building again trading off components against one another as long as the proposed design's energy budget is less than the standard design's energy budget.  Some of the fenestration limitations on this approach are:

• U-Factor < 0.4 in zones 4 to 8
• SHGC < 0.55 in zones 1 to 3
• Standard and proposed design interior shading factors must be equal (0.7 summer, 0.85 winter)

Note, the 2004 IECC performance analysis now uses energy cost, not consumption, for comparison (similar to ASHRAE's methods.) This means that electicity use is penalized since it is an expensive fuel.  For fenestration, this means that SHGC may be more heavily credited in the design since a SHGC reduction will result in reduced cooling cost which is electrically driven.   This fact may allow the designer to trade off against other components more easily.