Comparable in importance to the selection of plants is the choice of nonplant construction materials for the outdoor room. Essential for architectural and engineering functions, the construction materials available are nearly as diverse as the plant materials that a designer must choose from. A good designer must know the characteristics, potential uses, and availability of various woods and pavings, of materials that may be precast, quarried, or prefabricated. Landscape designers can also benefit from the personal experience of working with construction materials in order to understand the difficulties encountered when they are specified for particular uses. Several excellent construction specifi­cation manuals are available for reference. These are updated regularly to keep professional designers abreast of current materials, their dimen­sions, strength, potentials, and costs. The following comparison of some common construction materials will serve as a simplified introduction to a complex subject.

Enclosure Materials

Enclosure materials form walls for the outdoor room. As such, they function in many ways like the walls of indoor rooms. In addition, they often do things that indoor walls do not do. The particular enclosure material selected will depend on whether the purpose is to offer

• strength, as with a security fence or a retaining wall.

• privacy, requiring a height of at least 6 feet and the properties of solidity and nontransparency.

• climate control, which may necessitate the strength to withstand and divert strong winds or high snowdrifts.

• space articulation, which may require height and screening, or nothing more than a suggestion of the room’s limits, permitting attractive off-site features to be seen.

Much of the enclosure material available today is prefabricated. It may also be constructed on-site, using materials such as wood or stone, poured or precast concrete, brick or railroad ties. Figure 9-31 compares commonly used landscape enclosure materials and several representa­tive styles.