Volume 8, Issue 3 - March 2007

AAMA Analysis

Manufacturers, Listen Up
Residential Codes Now Require Mullion Compliance
by John Lewis

The qualification of mullions is an interesting case study in how fenestration performance concerns find their way into industry standards and, ultimately, into building codes.

As mentioned in this column in the October 2006 issue (page 8), the performance of mulled assemblies first gained higher-profile attention in the wake of studies analyzing the damage wrought by the severe 2004 and 2005 hurricane seasons. Some of these studies concluded that mullions in combination assemblies had frequently not been built or tested to meet a standard and often showed disappointing performance, such as excessive water leakage. 

Meeting the Code

The touchstone for mullion performance is AAMA 450, Voluntary Performance Rating Method for Mulled Fenestration Assemblies, which first defined procedures for determining the air leakage resistance, water penetration resistance and structural performance of mulled assemblies back in 2000. 

The standard, updated in 2006, is referenced in AAMA/WDMA/CSA 101/I.S. 2/A440-05 for the performance of a combination unit (an assembly of individual window units whose frames are joined together at the factory or at the point of installation, using a mullion). This has formed the basis for optional certification of mulled assemblies under the AAMA Gold Label Certification Program for air-water-structural performance. 

The presence of an AAMA Gold Label with an integral or separate AAMA 450 tab is now recognized as evidence of compliance of combination assemblies with the new 2006 International Residential Code (IRC). The requirement is that “mullions shall be tested by an approved testing laboratory in accordance with AAMA 450, or be engineered in accordance with accepted engineering practice” (Section R613.9.1 Mullions). 

The individual units of combination assemblies must first be tested per 101/I.S. 2/A440-05. There are then several options available for demonstrating compliance of the entire assembly with the 2006 IRC. For manufacturers participating in the AAMA Gold Label Certification Program, whose combination assemblies have been qualified by testing and/or calculation to AAMA 450, the simplest and preferred approach is to apply the AAMA Gold Label with an integral AAMA 450 tab. In this way, a building inspector can tell easily if the combination unit complies. 

An optional way to demonstrate compliance, outside of AAMA certification, is to label the individual component units for conformity with 101/I.S. 2/A440. A single label will suffice if all component units are identical. A manufacturer-generated label indicating compliance with AAMA 450 can then optionally be applied, or test reports for the entire assembly can be kept on file. 

Outstanding Issues

Section R613.9 of the IRC states that if the mullion device is tested as a stand-alone unit, it must comply with the indicated performance criteria for load transfer, structural safety factor and deflection. As to the latter, section R613.9.3 requires that “mullions shall be capable of resisting the design pressure loads applied by the door and window assemblies to be supported without deflecting more than L/175, where L is the span of the mullion.”

This requirement could cause some confusion among manufacturers, as 101/I.S. 2/A440-05 requires the L/175 deflection limit for HC and AW rated products, but not for R, LC and C grade products. 

The IRC, however, does impose the limitation for stand-alone mullions intended for residential-class buildings. Some state jurisdictions are imposing their own additional requirements.

Application issues such as this will be ironed out, and are prime examples of why participating in association standards development and code liaison activities should be key elements of any manufacturer’s business plan. 

John Lewis serves as technical director of the American Architectural Manufacturers Association in Schaumburg, Ill. He may be reached at jlewis@aamanet.org.


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