AGG - 2006 - March/April - An A For Aluminum

Volume 20 • Issue 2 • March/April 2006

Metal Matters

An A for Aluminum

By Greg McKenna

Aluminum has been the metal that matters to curtainwall systems through most of the last century. It has a high strength-to-weight ratio, is extremely durable and can be extruded into a wide variety of shapes. As the construction industry demands faster building times, higher performance and increased environmental awareness, today’s advanced curtainwall systems must combine ease of fabrication and installation with high performance while maintaining the architect’s design intent.

In the 1930s, aluminum windows increased in popularity because of the many benefits aluminum provided over windows made from other materials. It was during this time, in 1932, that Kawneer installed its first aluminum curtainwall in the U. S. Post Office in St. Paul, Minn. These early curtainwalls were custom designed and engineered for each project. It was not until 20 years later, however, that architects fully embraced aluminum and glass curtainwalls. This trend led manufacturers to offer standard “off-the-shelf” curtainwall products. In the 1950s and 1960s several generations of unit wall were introduced. These pre-designed, pre-assembled systems were available in a number of standard and optional configurations for use on one- and two-story applications and allowed for frames to be fabricated and assembled in the shop. Typically, the two piece mullion designs allowed for stacking of the frames together in the field. Frequently, early “standard” systems were made from all-aluminum frames that held monolithic glass. It was not until the end of the 1960s that improvements in thermal performance were incorporated into the designs to meet higher thermal performance demands.

Today, controlling field cost and ease of fabrication are paramount. Outside glazed stick built systems continue to be the most popular solution for low-rise buildings. High-rise buildings, however, often require inside glazing so that the glass can be installed from the floor slabs rather than from exterior scaffolding. On-site construction costs can be further reduced by specifying “unitized” systems where, in addition to being assembled in the shop, glazing can be added at this stage. Like its early predecessors, today’s pre-assembled and pre-glazed systems reduce installation costs without compromising performance.

Current systems are tested to much more rigorous standards for air, water and structural performance than in the past. Additionally, products are often tested for thermal, seismic, hurricane and acoustical performance.

When considering innovations over the years, energy efficient designs have experienced the greatest technological advancements. Today’s aluminum curtainwalls are “thermally improved” by low conductance pre-formed thermal barriers and pour-in-place polyurethane thermal barriers. Improvements in glass fabrication now produce high performance insulating units containing low-emissivity (low-E) coatings which further reduce thermal transmission and solar heat gain.

Architects are concerned with environmental impact today more than ever. LEED certification has come to the forefront and aluminum curtainwalls and their associated components provide sustainable solutions. Beyond the inherent recycling benefits, availability of solvent-free powder coatings adds a “green” element that makes aluminum the material of choice. Additional requirements are met via the combination of high thermal performance curtainwalls and the incorporation of sister products, such as sun shades. Light shelf accessories can be added to project daylight further into the building’s interior or overhead glazing can be used in sloped and skylight applications to bring direct sunlight into the building’s interior.

After 70 years, curtainwalls have evolved and changed but the metal is still the same. Aluminum will continue to provide diverse opportunities for the curtainwall systems of the future.

Greg McKenna, P.E., is product manager, curtainwalls for Kawneer Co. Inc., Norcross, Ga.