Plastics: There is clearly too much plastic in C&D waste, some of it contains heavy metals such as lead, and some of it (notably PVC) generates dioxin in production and disposal (see Chapter II). New kinds of bio-plastics can be helpful, but much plastic needs to be eliminated, and whatever is used needs to be more easily separated from other materials. Some waste plastics can be shredded and used as filler in other materials such as concrete, and plastic waste materials from households can also be recycled to obtain artificial lightweight aggregates for mortars (Elias-Ozkan & Duzgunes, 2000). This brief discussion only touches on a small portion of considerations related to building materials. As suggested at the beginning of this chapter, there are also many economic and general infrastructural considerations that currently militate against both recycling and reuse. And cultural factors are also involved. Sassi (2000), for example, points out that UK studies show that many materials are junked well before their service life is exhausted, with only 25 percent of materials replaced because of maintenance. That is, most renovation is done for reasons of style or function that has nothing to do with materials wearing out. Nevertheless, even before new forms of liability (like extended producer responsibility) and design for disassembly are implemented, the potential for recycling and reuse is great. The following table summarizes a 1997 study by the US National Assn. of Homebuilders which gives some sense of the technical potential in residential building for deconstruction and recycling in current conditions . Note that the numbers do not include a full, poured-concrete basement.