Windows and Sustainability: An Environmental Perspective

Windows and doors can contribute to green design and LEED® credits
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The prototype condominium is 10,000 sf, with 1,500 sf of glazing, and five condos of 2,000 sf each. Windows are located on all four building elevations, and include shading (interior shades, overhangs, and trees). Heating is by gas furnace, with air conditioning for cooling.

The analysis for a cold climate like Madison, WI indicates wood or vinyl frames save seven percent on annual energy costs over aluminum frames. The results are typical for buildings occupied 24 hours a day, such as assisted living facilities, apartments, condominiums, dormitories, and single-family homes. Office buildings and schools will have reduced heating loads due to internal heat generation from lighting, equipment, and higher densities of people. These buildings will have higher cooling loads and the percentage of savings may be lower.

A more temperate climate, like Kansas City, MO, indicated a seven percent savings in yearly energy costs with wood and vinyl frames. In the hot climate of Phoenix, AZ, wood or vinyl yields a six percent annual energy cost savings over thermally-broken aluminum frames. Savings over aluminum frames without thermal breaks are much higher.

At Burlington apartments in Portland, OR, Ankrom Moisan Associated Architects specified wood windows to meet the developer's energy-efficiency requirements more cost-effectively than aluminum.

Courtesy of Pella Corporation

Recyclable: Aluminum and wood are typically recycled for various purposes. There is debate within the building industry about the feasibility of recycling vinyl windows. The Vinyl Institute claims that vinyl windows are recyclable, while a 1999 EPA report stated that most PVC products are disposed of either through landfills or incineration, with only a small percentage that are recycled, roughly three percent in Europe and less than 0.6 percent in the U.S.

Aluminum can be recycled, during manufacturing and before building demolition. Recovery of aluminum from demolition and replacement in the building industry is minimal compared to recovery from the consumer goods sector. Of the estimated 400 million pounds of aluminum potentially available, only 15 to 20 percent is recovered. According to the National Resources Defense Council, aluminum should be used in applications where high recycling rates can be achieved and where its unique properties are indispensable.

Environmental Comparison of Window Framing Materials
Criteria
Aluminum
Wood
Vinyl
Source Material
+
Renewable
+
Recycled content
+
+
?
Embodied energy
+
Pollution produced
+
Energy consumed
+
+
Recyclable
+
+
?
Biodegradable
+


"Aluminum frames cause the highest burden to the environment because of the dangerous pollutants release and high energy consumption during aluminum production. PVC contributes large amounts of poisonous pollutants throughout its life cycle, while wood window frames have the least environmental impact."

Source: Life Cycle of Window Materials − A Comparative Assessment, June 2002
+ = favorable environmental impact
? = environmental impact uncertain

Biodegradable: Among aluminum, vinyl, and wood, only wood is biodegradable. Biodegradable materials can break down into the raw materials of nature and disappear into the environment.

A report studying life cycle assessment by USGBC, "Assessment of the Technical Basis for a PVC-Related Materials Credit for LEED," (LEED Technical and Scientific Advisory Committee PVC Task Group, February 2007), concluded that aluminum window frames, with or without thermal breaks, are consistently the worst material relative to environmental impact when compared to the vinyl and wood alternatives reviewed.

Overall, studies from the U.S. and the U.K. analyzing the life cycle assessment of aluminum, vinyl, and wood window frames, based on production, energy consumption, environmental impact, and other factors, support the conclusion that wood window frames have the least environmental impact.

"Wood frame windows bring an organic quality to projects, which cannot be replicated by other types of cladding. They provide great LEED performance ratings, sustainable design, and occupant comfort," says Celeste Novak, AIA, LEED-AP, principal, En/Compass Architecture, Ann Arbor, Michigan.

In selecting resource-efficient windows for the Prairie Learning Center, OZ Architecture specified aluminum-clad wood windows with argon-filled, Low-E insulating glass and triple glazing with integral blinds.

Neal Smith Wildlife Refuge/Prairie Learning Center, Prairie City, IA. Oz Architecture

Conclusion

The USGBC's LEED Green Building Rating System has become the benchmark against which to measure sustainable buildings in the U.S. The major LEED categories enable design professionals to analyze building project components and related issues that contribute to sustainability and environmental best practices.

Based on a detailed analysis of LEED categories, windows and doors can contribute to one prerequisite and up to 25 of the 69 points toward LEED certification. When comparing aluminum, vinyl, and wood frame windows, wood windows provide the greatest sustainability benefits and least environmental impact on the environment.

Barbara A. Nadel, FAIA, principal of Barbara Nadel Architect, in New York City, frequently writes about design and technology. She is the author and editor-in-chief of Building Security: Handbook for Architectural Planning and Design (McGraw-Hill, 2004).

 

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Originally published in May 2007

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