A key mulling concept to understand is AAMA 450 Certification, a performance certification rating that is typically required in commercial or high-end residential projects and used as a standardization method for rating a mulled window wall assembly. AAMA 450 evaluates air, water and structural components and establishes a performance grade rating (PG) of the overall mulled assembly.
AAMA 450 Certifications are becoming more important as architects increasingly specify buildings with window walls, typically formed by mulled window assemblies. It helps to act as a quality control measure to provide assurances to all interested parties (i.e., owners, architects, installers, and builders) that the products are capable of meeting air infiltration allowances for energy purposes and structural requirements, as well as resisting water penetration into the interior of the building.
Ensuring mulled windows are certified is especially important for buildings and homes that require specific performance grades in certain regions. For example, the Northeastern coastal geographies have stricter codes than regions with more temperate weather.
Assembly Testing
For mulled assemblies, the AAMA 450 test will rate the overall assembly to the lowest rating between the individual unit and the mullion—since multiple window types with individual PGs come together to make one mulled assembly. If the overall assembly is not tested using the AAMA 450 standardized assessment, then the certification and PG rating of each individual unit is essentially a meaningless indicator of whether the assembly will satisfy specific building codes.
“There have been situations where our products have been put in applications without an understanding of the product limitations and environmental stresses,” says Jeff Siverhus, a senior product manager with Marvin Windows and Doors. “The contractor could be installing a PG 40-rated window assembly when a PG rating of 50 or 60 is required.” Inadequate mull reinforcement could lead to leaking or even catastrophic window wall failure.
More Project Confidence
The International Building Code requires either physical testing or calculations to determine mulled window performance. Siverhus says Marvin tests both ways. The dual determination presents a more comprehensive picture of the mull assembly’s performance, according to Siverhus.
Some window manufacturers also test more assemblies than others. Marvin and Integrity are industry leaders in testing mulled window assemblies for AAMA 450 compliance across many different PG configurations. The Marvin architectural detail manual (ADM) features dozens of performance charts addressing assembly scenarios across 11 different mulled window assembly types.
Single-Source Accountability
A comprehensive ADM offers home builders and architects with a wider array of AAMA 450-certified assemblies to select from. A tested, single-source window wall assembly built to an AAMA 450-certified standard helps simplify project design and management, speeds installation, and reduces callback risk. Learn more about Marvin and Integrity mulling solutions.
