For slopes, the incline should not exceed a rise of 1 foot vertical change for every 2 horizontal feet—referred to as a 2:1 or 50 percent slope (Figure 11-20). For curvilinear design themes, the base plane might be gently sloped and contoured with gradual transitions from one space to another (left side of Figure 11-23). The greatest feeling of enclosure is gained when the ground fills a 45-degree cone of vision or extends above eye level (Figure 11-17). A rectangular design theme can be reinforced with retaining walls or rigid slopes (right
Slopes and retaining walls should relate to and reinforce the established design theme. The height of the surrounding ground can be varied to give different feelings of enclosure. Figure 11-18
Plant materials can be used to accentuate the height of ground around a space. The first and simplest method is to provide an elevation change between two adjoining spaces (Figure 11-14). The designer might also use a combination of slopes and retaining walls (Figure 11-22). In all situations, the height of the surrounding ground should be limited by several guidelines. In all these situations, the higher the surrounding ground, the greater the sense of spatial enclosure. When enclosing space in the vertical plane, the designer should use slopes or low retaining walls to reinforce the style or design theme established by the form composition. Figure 11-14
A feeling of space can be created by a simple grade change between adjoining
mounds to provide spatial enclosure (Figure 11—15), or both excavated and filled (Figure 11-16). Slopes steeper than this are subject to slippage and erosion. There are several aesthetic purposes for grading on a residential site. The greater the change in elevation between spaces, the greater the feeling of spatial separation. The slopes should move around the outer edge of the curves to reinforce their form in the third dimension. Full enclosure with surrounding ground is most appropriate where a sense of privacy is desired, such as in a small sitting area or private outdoor lounging area. First, grading can define edges between spaces and partially enclose space in the vertical plane. Figure 11-19
The location and height of ground can be varied to provide different degrees of enclosure. Whatever height is
Vertical planes around a space can be created by excavating into the existing ground or building on it with earth mounds. Often, a space requires enclosure on only one side with a more open feeling provided on another (Figure 11-19). Grading can also be used to provide vertical planes around the outside of a space for implied enclosure.