The Green Guide to Specification also provides evaluation methods for various window options.

Of all four materials, wood has the lowest embodied energy. It takes only 3,770 BTUs of energy to produce a pound (BTU/lb) of wood. Wood frames also are recyclable if and when they are no longer in use and are biodegradable if the products are disposed of into the environment. Additionally, the softwood used for window frames is obtained from rapidly renewable resources; the net volume of wood in U.S. forests is increasing because of sustainable harvest techniques.

Aluminum contains bauxite a non-renewable resource and takes the most energy (103,500 BTU/lb.) to produce from raw materials. But aluminum extruded from recycled materials uses only 20,700 BTU/lb. Aluminum frames also are recyclable when their use has ended.

Vinyl depends on oil resources so it is not as environmentally acceptable. Vinyl window frame material also does not have recycled content and takes 36,500 BTU/lb to produce. It is unclear whether vinyl is recycled or recyclable. The Vinyl Institute indicates vinyl window frames are recyclable, but the U.S. EPA states only a small percentage of vinyl-0.6% in the United States and 3% in Europe-is recycled.

Also, the USGBC is re-evaluating its position on vinyl. During early LEED development a credit was proposed for the avoidance of vinyl in building products. Questions have been raised that available science shows no grounds to support this exclusion of vinyl. The USGBC Technical and Scientific Advisory Committee has begun a comprehensive study on the matter and intends to publish its final report in late 2005.

Fiberglass has very low embodied energy. It is a natural insulator with low expansion/contraction rates and thus maintains dimensional stability year round. Fiberglass also has self-extinguishing capabilities in case of fire and does not emit toxic fumes.