Ensuring Performance in Mulled Window Systems
When specifying fenestration, design professionals must select appropriate products for the project’s various opening sizes. However, today’s construction landscape is rapidly changing with higher material costs, tight tolerances, and expectations of floor-to-ceiling glazing in multifamily projects.
Many project teams are opting to specify delegated design mulled window systems that combine multiple windows into a single unit in a larger glazed opening, rather than a storefront or curtain wall system. While these mulled systems have become increasingly popular, their mulling components can create potential performance issues, including air infiltration, water penetration, structural failure, and reduced thermal performance.
Highlighting examples from past projects, this article explores the rationale and risks of using mulled window systems; reviews methods for addressing these risks; and demystifies standards, such as NAFS-17 and AAMA 450-20, that are crucial for design professionals specifying window performance.