The Benefits of Aluminum Windows
- By R.C. Goyal
- August 1st, 2002
Why is aluminum the framing material of choice in both new construction and replacement windows for college and university buildings? Aluminum has long been favored for sheet metal, aircraft and many automotive applications. Its relative strength, durability, repairability and flexibility of design make it ideal for campus building windows and doors.
Aluminum is the most readily available fenestration framing material, made from bauxite, a plentiful mineral easily converted to this versatile metal. A material with a high strength-to-weight ratio and easily formed into any shape, aluminum is not only the most common commercial framing material, most of the world’s tallest buildings are encased in it. Its hard surface resists denting and weathering. It can be painted in virtually any color, including historic window colors, providing long-lasting aesthetic appeal.
And when an aluminum product’s life is over, it can be recycled into other products without losing any of its structural properties.
The extruded aluminum used in commercial windows is actually an alloy composition that includes trace amounts of silicon, iron, copper, manganese, magnesium and chromium, as well as aluminum.
The Most Successfully Recycled Material
Aluminum is a surprisingly “green” building material, with 45 percent to 50 percent reconverted into other usable products. No other material comes close; metal or nonmetal. It takes only 5,000 btus of energy to convert scrap aluminum to usable material. Vinyl, wood and steel take up to three times as much energy to reprocess.
Aluminum Meets Architectural Glass Deflection Standards
In the commercial window and door industry, one of the most frequently specified criteria by architects is the glass deflection limit -- expressed as L/175 -- for all glass holding members. This is important because large commercial windows, such as those used in schools, must be able to withstand significant windloads without appreciable deflection and potential damage. Aluminum fenestration products easily make these requirements, whereas other nonmetal framing materials have difficulty achieving this safety design requirement.
The superior structural strength of aluminum windows and its resistance to deflection afford the industry’s best resistance to water and air infiltration caused by glass deflection, which can compromise the integrity of the seal against outside elements. The larger the window, the more pronounced aluminum’s structural strength advantage versus nonmetal framing materials.
A U-Value Comparison With Wood and Vinyl
While both wood and vinyl frames share a slightly better energy resistance factor than aluminum, this edge was long ago minimized with the addition of the thermally broken insulated glazing system common in all windows today.
Indeed, the aluminum window industry first addressed its perceived energy deficiency nearly a half century ago with the invention of thermally broken aluminum windows. If everyone had used thermally broken windows with insulated glass since the early 1950s, perhaps we would not be facing an energy crisis today!
It is also important to note that, since the ’50s, the evolution of high-performance glazing systems -- often combining low-e coatings, gas filling and warm-edge spacers -- has narrowed any thermal advantage that one window framing material has over the others. The relative importance of frame thermal performance (vs. total unit performance) is further diminished in the larger window sizes, most commonly used in educational buildings, where aluminum may be preferred for its superior structural strength.
Even Wood Windows Feature Aluminum-Clad Exteriors
Aluminum is the preferred exterior surface for most school windows, including those made from wood. That’s because aluminum won’t rust, warp or absorb moisture, and it has low expansion/contraction characteristics. These attributes allow aluminum cladding to enhance wood windows’ weatherability and minimize maintenance.
The metal’s maintenance-free performance is reinforced by its long-lasting finishes (including Kynar 500). It’s a surface that resists chipping, cracking and denting. When scratched, it can be easily refinished to its original appearance.
In the interior, solid aluminum windows are far more resistant to normal wear and tear. They won’t scuff like vinyl or dent like wood, both of which can sustain surface damage beyond repair.
R.C. Goyal is chairman of Aluminum Materials Council, American Architectural Manufacturers Association and may be reached at 909/587-9700 or .