Sustainable Building Technical Manual - Etn-presco.net

❑ Carefully distinguish between light-vehicular, heavy-vehicular, and pedestrianp a v i n g .In landscape design, vehicular-strength paving is often used by default even for sidewalks;this unnecessarily eliminates beautiful alternative materials, and wastes materialsand money, since many paving materials are non-renewable and energy-intensive,and should not be wasted.❑ Use water-permeable or “porous” paving.Porous asphalt and concrete are made with aggregates carefully sorted to eliminate“fines” (small particles). Removing fines opens voids that allow drainage, yetporous paving retains most of the strength of conventional paving. Porous pavingis suited to parking and lightly used roads; in high-traffic areas, combine it withconventional paving. 8Other permeable systems include block-lattices, which permit drainage but give stability(grass grows in the lattice spaces, while the blocks support vehicles). Lattices are bestused for occasional access (fire lanes, overflow parking); constant traffic may kill thegrass, as may harsh climates. Some permeability can also be achieved by setting traditionalstone or masonry pavers on sand instead of on concrete.❑ Design paving to serve dual purposes.Porous paving is often constructed over a gravel reservoir sized to hold stormwater volume,thus combining parking and a retention basin within a single area. Such spacesaving is both economically and environmentally sound.❑ Design to minimize runoff.Curbed pavement edges concentrate runoff, which increases potential for erosion andflooding. Where possible, porous gutters and curbless designs spread run off moreusefully. In general, runoff should be infiltrated as close as possible to its source; flowconcentrated over long distances picks up speed and erosive power, and disrupts thedistribution patterns of natural precipitation. Infiltration at the source is also morecost-effective (see also Chapter 6, “Water Issues”).❑ For light-duty roads and paths, stabilize without pavement.Correctly installed, crushed stone or brick is a stable, porous surface. Proprietary chemicaladditives can bond soil particles for stability. Geotextile webs and strips are used,much like the straw in traditional adobe, to increase soil strength without affecting itsdrainage or growing characteristics. Such surfaces are slightly flexible, which minimizescracking and decreases maintenance costs.❑ Locate pavement where solar heat gain is desirable.Texture, type, and color of pavement can reduce or concentrate heat or glare if coordinatedwith prevailing climate conditions. Coordinate paving design with plantingsand shade structures to avoid glare and unwanted heat gain. These factors are particularlyimportant in hot and cold environments. 9Materials for Site Construction and Furnishings★ S I G N I F I CA N C E .Careful selection of site construction materials can reduce energy consumption andwaste, increasing human comfort without excessive environmental costs. Inappropriateselection of materials can cause resource depletion and environmental contamination,either at the site or at the source of the material. Many environmental effects of resourceuse are indirect. Only a few common site materials are directly toxic to soils or plants;