07/01/2008

Shedding Light on Curtainwall Systems

Curtainwall systems can meet both the functional and aesthetic requirements of your façade

 

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The Float Process Defined
Invented by Sir Alastair Pilkington in 1952, the float process made it possible to create the large areas of glass needed for curtainwall systems. The process, which results in smooth, polished glass with nearly parallel surfaces, involves taking molten glass at approximately 1,832 degrees F. and pouring it continuously into a shallow bath of molten tin. The glass "floats" on the tin, eventually forming a level surface. The speed at which the hardening glass is drawn off the bath helps control how thick the glass will be. While the original float glass was only 6-millimeters thick, today, glass can be formed with thicknesses between 0.4 millimeters and 25 millimeters.

Source: Pilkington

By Helmut Kientz

Found primarily in commercial and institutional design, curtainwall systems serve as a design element that can protect building occupants from the extremes in weather while moderating the effects of thermal expansion and contraction, building movement, and more.

First used in the early 20th century, curtainwall construction is not new. The original curtainwall system featured infill material made of metal; the advent of the glass-float process in the 1950s, and development of new thermal and construction technologies in subsequent decades, have led to the escalating use of the curtainwall systems used in design today. Now, in addition to metal, infill materials can be made of monolithic or insulating glass, stone veneer panels, louvers, and even operable or fixed windows and vents.

Although the infill material comprises most of the curtainwall system, it is helpful to understand the types of curtainwall systems available, as well as some points to consider when designing curtainwall systems.

Types of Curtainwall Systems
There are five curtainwall types that are in use today:

  1. Stick System (Fig. A). In the stick system, mullions (sticks) are fabricated in the shop and installed and glazed in the field. Sticks are placed between floors vertically to support individual components, such as horizontal mullions, glazing, and spandrels. Loads are transferred through connections at floors or columns.
  2. Unit Panel System (Fig. B). For large or labor-intensive projects, unit panel systems may be a cost-effective alternative to the stick system. In the unit panel system, panels are fabricated and assembled at the shop, and may be glazed there as well. The panels are then taken to the field, where they are attached to a building structure.
  3. Unit and Mullion System (Fig. C). Similar to the stick system, mullions are the first tube to be installed in the unit and mullion system. Spandrel and glazing, however, are inserted into the stick system as a complete unit.
  4. Column Cover and Spandrel System (Fig. D). While column cover and spandrel systems are similar to unit and mullion systems, they differ in that the building frame is emphasized with column covers, which act as sticks.
  5. Point Loaded Structural Glazing System (Fig. E). In this system, the vertical framing member can be comprised of stick, cable, or another custom structure behind the glass. Glass is supported by a system of four-point brackets, and joints are sealed with silicone.

 

Issues to Consider with Curtainwall Systems
Like any building systems, curtainwall presents several issues that must be considered during design and construction. In addition to air infiltration and deflection, non-deflection-related stress and thermal conductivity loads are, perhaps, the top issues to consider. Because curtainwalls are designed to be non-load bearing, any loads placed on the curtainwall—such as those from the curtainwall elements (e.g. mullions, infill, etc.), weather (e.g. wind and snow), seismic and blast forces, and thermal—must be transferred back to the structure itself.

Fire safety is another area of consideration. Because gaps between floors do little to impede fire and smoke, fire safing and smoke seals should be located between floors to maximize protection. In addition, tempered knockout panels, designed to fracture and provide access during a fire, should be included to reduce safety concerns.

Finally, note that curtainwall systems typically cost more than standard window systems. These costs must be reviewed in conjunction with the need to address special design considerations, such as support framing, glazing types, interior vs. exterior systems, shading devices, applied finishes, special infill materials, etc.

 

An Ounce of Prevention
Beyond these issues, a variety of factors can influence the performance of a curtainwall system. Air and water infiltration, the quality of materials and installation, and other issues can all lead to curtainwall failure.

To maintain the life and protection of the curtainwall system, periodic checks of items, such as gaskets, seals, system joints, and the thermal-insulation capabilities of vision and insulating panels, should be conducted, and aluminum frames should be cleaned. Furthermore, perimeter sealants, typically designed to have a service life of 10 to 15 years, should be carefully removed or replaced at the end of their life.

Helmut Kientz is senior architect, design and illustration, at Cincinnati-based Hixson.

 


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Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.


Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.


When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.

 


Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.


Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.

 

Replace core drilling with Connectrac In-Carpet and On-Floor Wireways, the proven connectivity solution in open interior spaces of all kinds. These elegant low-profile wireways are great for AV / telecom connectivity wherever it’s needed.

 

Add highly responsive multi-zone comfort to any building project, in any climate. Our CITY MULTI H2i R2- and Y-Series VRF systems give you flexibility to fit the needs of any building. Enjoy 100% heating capacity at 0°F outdoor ambient, and 85% heating capacity at -13°F outdoor ambient.  For more information, log on to www.mitsubishipro.com


 
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