Unlike the other elements of the hardscape system, floors need to withstand traffic. You have a wide range of serviceable materials to choose from (many of which won't lay waste to the planet).
From a sustainability point of view, many flooring materials have unacceptable negative effects. The off-site impacts of getting the materials in the first place can be extreme: strip mining, clear-cutting forests, dredging riverbeds, or drilling for oil. The processes used to turn raw materials into finished products can be energy-intensive, toxic, climate-changing, and hazardous to workers. Installation can involve heavy equipment, fossil-fuel use, and lots of noise. Surfaces that require periodic maintenance can make unreasonable demands for chemicals and energy.
You'll also find some sustainable imposters — materials that have questionable or fraudulent environmental credentials. These materials include plastic lumber, phony plastic lawns, and mulch made from ground-up tires. Plastic lumber isn't all bad, but the phony lawns and mulch are environmental nightmares.
Stick with materials that are as close to a state of nature as possible and that require minimal processing and maintenance. And, build things so they last; durability is a supremely sustainable strategy, because it divides the initial inputs over many decades of use.
There's a difference between concrete and cement. Even professionals don't always understand this, so if you do, you'll be among the initiates into the Mysteries of the Cementitious Realm. Here's the scoop:
The manufacturing of cement for concrete production is incredibly energy-intensive, and it generates 5 to 10 percent of the world's carbon dioxide emissions, but improvements in the processes used are lowering that figure dramatically. New technologies such as nano-concrete (made with a special kind of cement that has a much lower environmental impact) are very promising. And believe it or not, a new type of photocatalytic concrete (using a technology called TXActive) actually absorbs air pollution.
Because rainfall runs off of solid paving, it can be an unfriendly part of the watershed, causing flooding and stream pollution when the water spills into the street and carries contaminants into waterways. Choosing pervious surfaces is one way to deal with that concern, but you can also purposely choose impervious surfaces to act as water catchment zones that spill their captured water into bioswales, planted areas, or other spots where it will be put to use. (See the later section "Using safe, sustainable materials" for more information on pervious materials, and refer to Chapter 8 for details on water harvesting.)
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