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FGIA updates Performance Rating Method standard for mulled combination assemblies

January 20, 2021  By FGIA

The Fenestration and Glazing Industry Alliance (FGIA) has updated a mulled assemblies document. AAMA 450-20, Performance Rating Method for Mulled Combination Assemblies, Composite Units, and Other Mulled Fenestration Systems, was last updated in 2010. This FGIA performance rating method describes procedures and requirements for determining the air leakage, water resistance and structural performance of mulled fenestration systems.

This method describes test procedures and calculation procedures for determining the performance of mulled fenestration systems. Mulled fenestration systems may be factory assembled or knocked down for field assembly with parts and instructions supplied by the fenestration product manufacturer.

“The North American Fenestration Standard says that ‘mullion ratings shall be determined according to the requirements and procedures of AAMA 450 for both composite units and mulled combination assemblies.’ However, until now, AAMA 450 provided no guidance for composite units,” said Dave Goldsmith (PlyGem), co-chair of the FGIA Requirements for Mulled and Combination Window Assembly Update Task Group.

Composite units have been brought fully into the scope of the standard, together with storefront and curtainwall fenestration products and side-hinged doors.


“This will put powerful new tools into the hands of engineers to assist them in determining how to construct structurally sound and weatherproof fenestration products in the most economical ways, and should also drastically reduce the amount of testing required to validate a large variety of composite unit configurations,” said Goldsmith.

AAMA 450-20, as well as other AAMA documents available from FGIA, may be purchased from the online store at the discounted member rate of $20 or the non-member price of $60.

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