Eliminating the Potential for Air and Moisture Infiltration in Stucco Facades at the Window-Wall Interface

Functional performance at the window-wall interface in stucco facades has a significant effect on overall building envelope system performance. While building envelope materials, design and construction have exhibited a number of improvements in recent years including increasingly stringent code requirements, along with the general acceptance of air barriers and vapor protection and the introduction of whole building envelope commissioning, the window-wall interface continues to be a problem.

In 2008, the Western Construction Consultant Association (WESTCON) set out to test commercially available flashing systems for a standard storefront window in a stucco application. Their results were presented at RCI’s 2009 Building Envelope Technology Symposium.1 The WESTCON study began with a literature review, which revealed that there is limited guidance available for flashing aluminum storefront windows that lack attachment flanges. Of the six assemblies tested, two were considered successful, while the others leaked. Based upon the fact that the majority of the assemblies tested experienced problems, a team was assembled to investigate how the connection around the window and/or wall assembly within a stucco façade could be modified to improve leak-free performance. The process began with determining what testing would be required to confirm components incorporated in the design would be compatible and what standards must be met.

A description of product and independent laboratory testing for air infiltration, water-resistance and structural performance as well as vapor permeance and testing protocols will be reviewed in our BEST3 presentation2 and are summarized here. The presentation includes the evaluation of the ability of drift joints in the test assembly to meet seismic performance requirements by using a modified AAMA racking test with testing showing little difference in air exfiltration and air infiltration rates before and after the racking test.