• Field Notes 14.04.2010 1 Comment

    Having grown up in Philadelphia, I love U.S. history. On family vacations, my parents would take us to see presidential libraries as well as other historical sites. At one time or another, I’ve been through the Truman, FDR, Wilson, and Carter libraries, and would have made the Eisenhower in Abilene, KS, a stop if it hadn’t been 6:00 in the morning when we went by. In retirement (one day), I’d like to visit them all.

    In 2002, I got to actually participate in building one: the Clinton Presidential Library in Little Rock. I was working for CDC in Dallas, who, under contract to BHN, the glazing subcontractor, prepared the shop drawings and fabrication drawings for eight of the nine curtain walls employed on the project.

    The library itself is certainly different. One architectural critic called it a “mobile home on stilts.” Adjacent to downtown Little Rock, and located next to a train station turned into a university center and an abandoned railroad bridge over the Arkansas River, the building’s architect played on the president’s theme of a “Bridge to the 21st Century.” When it was completed, it was one of the better laid out, functional, thoughtful and more pleasant presidential libraries I’ve been through.

    But the particulars of the project made for some interesting issues as it relates to the curtain wall. As a museum first, the HVAC systems had to be designed to preserve the artifacts in the museum. That meant fairly high relative humidity (40-50%).

    And direct sunlight through the predominately glass west façade had to be mitigated so as not to cause the mementos on display to fade or deteriorate from the sun’s UV rays. An exterior screen wall of point-supported glass mounted on steel framing 10’-0” off the main curtain wall significantly reduced the sun from entering the main public spaces.

    Most of the curtain walls were small – under 3,000 square feet in some instances. Only one was larger than 10,000 square feet.

    My present employer would have gotten a kick out of this: eight of the nine walls we worked on were structural steel tubes clad with aluminum extrusions or stainless steel brake metal. Several of the walls were hung from the structure without mullions. Horizontal structural steel tubes, spaced 3’-0” vertically, ran between columns. The horizontals were tied to the columns for wind load support, but the dead load was carried by stainless steel rods positioned every 10’-0” on center to the structure above. The challenge was mounting and waterproofing the glazing pocket on the front of the steel to carry the 1 5/16-inch-thick insulating/laminated glass units.

    Most of the challenges came not from the curtain walls themselves, but from the integration of the curtain walls with other systems. For example:

    • Putting doors in a hung curtain wall can be a little tricky. If the structure supporting the curtain wall moves, it moves towards the door. And the door is supported off a different level than the curtain wall, thus making the door and wall usually moving (due to thermal or building movements) in the opposite directions.
    • Waterproofing the surrounding conditions and successfully transferring the air and water barrier line from the curtain wall to the surrounding substrates, often the sheathing behind a composite panel system. Again, due to HVAC and water issues, the sheathing was clad with a vapor permeable barrier, to which many sealants would not stick. We ended up specifying a flashing that the perimeter curtain wall sealed to, and then the panel subcontractor had to seal the flashing to the sheathing. But the rest of the sheathing and vapor permeable barrier was open for the transfer of humidity.
    • Coordination of the steel supporting the curtain wall between two different suppliers was hectic at times. Putting these all in one house would have simplified this matter a lot.

    It was a fun project, and I got to sit through the dedication on a cold, wet November day in 2004, and saw four U.S. presidents in attendance. Some projects will outlive us. But the memory of a good team and a money-maker for all concerned is the history lesson here.

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