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

Functional performance at the window-wall interface often has a significant effect on overall building envelope system performance. Building envelope materials, design and construction have exhibited a number of improvements in recent years. Code requirements have become more stringent and there is now general acceptance of air barriers and vapor protection. While most windows and curtain wall systems are designed and constructed to meet or exceed exterior wall performance requirements by code, building envelope repair and replacement costs in North America remains a multi-billion dollar expenditure. One study determined that over half of the building set examined experienced building envelope problems within the initial years of occupancy, and that most of the problems were moisture-related and were caused either by air leakage or exterior moisture penetration. The Construction Waterproofing Handbook published by McGraw-Hill states that “As much as 90% of all water intrusion problems occur within 1% of the total building or structure exterior surface.” These problems typically occur from improper design or construction practices and not material failure itself. Termination and transition details are of critical importance.

There are numerous issues at the window-wall interface that compromise the integrity of the building envelope which will be explored. The reasons for these problems will be discussed as well as curtain wall connection solutions. A logical solution to remedy these issues is the development of pre-engineered transition assemblies. The potential benefits are numerous: reduction or elimination of problems currently faced at the window-wall interface; the ability for the designer to specify one transition assembly flexible enough to be placed in many different locations and under different climactic conditions; and the ability to provide continuity and compatibility of performance layers between adjoining components/assemblies in a structurally sound and durable manner. 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. Case studies will also be included.