Curtain walls are widely used as exterior sheathing of buildings, especially of the commercial or institutional type. Curtain walls consist of glass panels constituting a major portion of the exterior surface of the building, with structural members separating the glass panels.
The structural members typically form a grid consisting of mullions (i.e., vertical members) and transoms (i.e., horizontal members). Panels are sealingly received between sets of mullions and transoms and supported thereby, so as to define the exterior sheathing of the building. In a rain-screen type of curtain wall system (zone drainage system), the framing about each glass panel defines a cavity between inner structural members and outer structural members. The inner structural members form a rain screen with the glass panel. The pressurized cavity between the inner and outer structural members defines a pressure zone of a pressure generally equal to that exerted on the outer structural member. The pressurized cavity is ventilated so as to allow air to enter or exit the cavity, in order to equalize the pressure in the cavity to the pressure at the exterior of the curtain wall. Accordingly, pressure increases, for instance due to wind or like atmospheric conditions, will be neutralized by the pressure zone and thus not cause infiltration through the rain screen.
However, curtain wall systems are still subject to water/air infiltration. Water/air infiltration through structural members is often through the intersection between the transoms and the mullions. More specifically, according to the type of construction of the mullions and the transoms, a caulking joint is often made between interconnected pieces. The caulking joint between the adjacent pieces seals off interface between interconnected pieces and is responsible for the water/air tightness of the curtain wall.
The efficiency of the tightness is related to the quality of joint being made between the interconnected structural members. As the sealing joints are made manually, and are exposed to great temperature variations and severe weather conditions, the water/air tightness of curtain wall systems is often inadequate such that there is infiltration.
Other constructions of structural members for curtain walls include a protrusion at ends of the transoms, which protrusions are received in corresponding notches in the mullions and are referred to as “penetrating transoms”. For instance, U.S. Patent Application No. 2004/0031220, by Hocker et al. and as published on Feb. 19, 2004 illustrates this type of configuration. The interconnection between the penetrating transom and the mullion reduces the risk of infiltration through the interface between the transoms and mullions.
In such systems, water collected by the transoms is drained by the effect of gravity and by the draining configuration of the structural members. More specifically, the transoms are positioned such that water accumulated thereon is drained toward the mullions. Accordingly, vertically adjacent sashes formed of structural members around a panel must be in fluid communication with one another so as to allow drainage of water on the surface of the mullions. Therefore, it is difficult to maintain a pressure equalization between the sash of a panel (i.e., a zone) and the surrounding pressure as all sashes communicate with one another. At present, systems with penetrating mullions are not used in rain-screen type of curtain wall systems due to the absence of isolated pressurized cavity about each panel.