The amount of shade desired will depend on the use of the space, the regional location, and the time of day when shade is needed. Therefore, walls and fences are best located to the east and/or west of the spaces that are to be shaded. regions that experience severe fire hazard (see “Protect from Potential Wildfires” in “Natural Events and Cycles” in this chapter). The best position for outdoor spaces used during a summer day is on the east or northeast side of the house or tree mass (Figure 3—16). The heat generated by exposed building roofs, walls, and ground surfaces radiates out into the nearby air, thereby elevating the temperature. ground plane. The shadow pattern on the ground plane can itself be an attractive quality in an outdoor space. Large and/or closely spaced members provide the most shade, whereas small and/or widely spaced members cast less shade. Vines can be grown on exterior masonry walls of a house to shield the exterior wall surface from absorbing the sun’s rays and converting them to heat, as discussed earlier. The broad intent should be to shield the sun from the house and outdoor spaces used during the summer season, especially during the afternoon hours. Second, shade trees provide relief from hot air temperatures through evapotran — spiration, a process of giving off moisture through leaf surfaces. Sun protection is most needed for the midday and afternoon hours during the summer season when air temperatures are the hottest. Figure 3-20
Vines on exterior walls and tall shrubs can provide shade from the low sun angle to the east and west. Exposure to the sun during these
Figure 3-16
Desirable locations for outdoor spaces during the summer season. Vine-covered or shrub-screened exterior walls are less useful on a south-facing wall because of the higher sun angle from this direction. Awnings and overhead structures are less useful for early morning and late afternoon/evening sun because of the lower angle of the sun at these times of day. However, a solid overhead plane can create a dark space below and may increase air temperatures by creating a cap that holds in the heat. Another consideration for creating overhead structures is the direction of the overhead members. The space between the individual members allows for heat to rise and escape through the overhead plane, thus helping to keep the space cooler. First, they block the sun’s rays from striking roofs of one — and two-story buildings, exterior building walls, and ground surfaces throughout the landscape. It has been estimated that a large shade tree can evaporate as much as 100 gallons of moisture per day, thus giving the cooling effect of five air conditioners.[3]
To provide shade, trees should primarily be located on the southwest and west sides of the house and outdoor spaces (Figure 3-19). When directly exposed to the sun, these surfaces convert sun rays into heat, which is radiated away from the surfaces (Figure 3-17). A mass of shrubs planted along an exterior wall will have a similar effect. Shade makes outdoor spaces more comfortable to use for longer periods of time during the summer. As a general guideline, people feel most comfortable in the following conditions: (1) shade, (2) no air movement, (3) air temperatures between 70 and 80°F, and (4) relative humidity between 30 and 65 percent.[2] This so-called comfort zone is exceeded when air temperatures rise above this level and/or there is direct exposure to the sun. Walls and fences also produce sun protection. A 25-foot-high tree located 10 feet from the west wall of a house may shade 47 percent of the surface while the same tree placed 20 feet from the wall will only shade about 27 percent of the surface.[4] One exception to this guideline is for
Figure 3-19
Shade trees should be located on the southwest side of the house and outdoor spaces for maximum benefit. The most common means is to strategically locate large shade trees to
shield the midday and afternoon sun from the residence and outdoor spaces used during this time of day. These same elements are also effective in casting shade onto the west wall of a house to relieve a residence from the intense heat buildup in this microclimate. Areas below trees may be 5 to 10°F cooler than nearby areas in direct sun. One is the density and pattern of the overhead members that cast shade. Shade trees can be placed in other locations as well to accomplish other design objectives, such as creating spatial edges or controlling views. These techniques are most effective on exterior walls that face either east or west because of the lower sun angle from these directions (Figure 3—20). A number of variables need to be considered when designing overhead structures. One way to accomplish this is to plan where outdoor uses are located with respect to sun. Overhead structures such as arbors, awnings, and pergolas can likewise be used to provide shade for outdoor spaces used during the summer months. By comparison, shaded surfaces do not heat up beyond the ambient air temperature and thus do not add to the temperature of the adjoining air mass or building interior. It is often better to create an overhead structure with multiple individual members spaced apart. Density aside, more shade will be cast by individual members that are oriented perpendicular to the direction of the sun (Figure 3—22). Vines and shrubs can also be used to shade the residence. An area immediately to the north of the house or a tree mass is also good, though the size of this shaded area is small because of the relatively high vertical sun angle shining from the south at midday in the summer. As this moisture evaporates from the leaf surfaces, it simultaneously cools adjoining air temperatures. An awning or solid rooflike overhead plane provides the most shade and is most useful over an outdoor space that is used extensively from midday through midafternoon. The size and spacing of the individual members has a direct effect on the amount of shade cast. Houses that are shaded may have interior air temperatures up to 20°F lower and have uncomfortable internal air temperatures half the time as long as houses that are not shaded.[5] This translates to reducing the need for air conditioning and the associated electric bill. times increases heat generated from exposed surfaces and reduces the ability of people and animals to shed heat from their bodies. Introducing elements that cast shade on a residential site can also create sun protection. Members that are placed at right angles in relation to the sun’s rays will provide more shade than members that are positioned parallel to the sun’s rays. Figure 3-17
Shade trees can shield roofs, exterior house walls, and the ground from the suns rays. These structures can stand alone or be attached to the house as an architectural extension. Still, the densest grouping of trees for shade should be placed to the southwest of areas that need shade. As with overhead structures, there are numerous design variables available to create a wide range of shade density.
