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on ecological systems. Sustainable construction considers the role and potential interface of ecosystems to provide services in a synergistic fashion. With respect to materials selection, closing materials loops and eliminating solid, liquid, and gaseous emissions are key sustainability objectives. Closed loop describes a process of keep- ing materials in productive use by reuse and recycling rather than disposing of them as waste at the end of the product or building life cycle. Products in closed loops are easily disassembled, and the constituent materials are capable and worthy of recy- cling. Because recycling is not entirely thermodynamically efficient, dissipation of residue into the biosphere is inevitable. Thus, the recycled materials must be inher- ently nontoxic to biological systems. Most common construction materials are not completely recyclable, but rather downcyclable, for lower-value reuse such as for fill or road subbase. Fortunately, aggregates, concrete, fill dirt, block, brick, mortar, tiles, terrazzo, and similar low-technology materials are composed of inert substances with low ecological toxicity. In the United States, the 140 million tons (127 million metric tons) of construction and demolition waste produced annually comprise about one-third of the total solid waste stream, consuming scarce landfill space, threaten- ing water supplies, and driving up the costs of construction. As part of the green building delivery system, manufactured products are evaluated for their life-cycle impacts, to include energy consumption and emissions during resource extraction, transportation, product manufacturing, installation during construction, operational impacts, and the effects of disposal.

LAND RESOURCES

Sustainable land use is based upon the principle that land, particularly undevel- oped, natural, or agricultural land (greenfields), is a precious finite resource, and its development should be minimized. Effective planning is essential to creating efficient urban forms and minimizing urban sprawl, which leads to overdepen- dence on automobiles for transportation, excessive fossil fuel consumption, and higher pollution levels. Like other resources, land is recyclable and should be restored to productive use whenever possible. Recycling disturbed land such as former industrial zones (brownfields) and blighted urban areas (grayfields) back to productive use facilitates land conservation and promotes economic and social revitalization in distressed areas.

Chapter 1

Introduction and Overview

Figure 1.3

Framework for sustainable

construction developed in 1994 by Task

Group 16 (Sustainable Construction) of the CIB for the purpose of articulating the potential contribution of the built environ- ment to the attainment of sustainable devel-

opment. (Drawing by Bilge Çelik.)

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