Several other approaches may also be taken to minimize exposure to cold wind. Proper planting of coniferous evergreen vegetation can save up to 30 percent of the heating cost for the cool season of the year.[10]
Specific site conditions such as available space, orientation of the house to the street, and direction of desirable views may not always permit coniferous evergreen vegetation to be organized around the outer northwest quadrant of a site. One potential application of this concept is to locate a wall or fence around the west and north sides of a front door entrance space on the north side of a house (Figure 3-32). Closely spaced coniferous evergreen trees function like a wall to direct wind up and over their mass, creating two protected zones (Figure 3-28). Figure 3-32
Coniferous evergreen plants and a wall/fence can protect a doorway on the north side of the house. Thus, one alternative approach is to mass coniferous evergreen shrubs immediately along the exterior wall of the house on the west and northwest sides (Figure 3-31). Coniferous evergreen trees and shrubs do this best because they possess relatively dense foliage throughout the year. To take advantage of their potential screening effect, coniferous trees and shrubs should be located on the west and northwest sides of the house as well as in outdoor spaces, where they can reduce the impact of cooling wind (Figure 3-29). How much wind protection is created and for what distance beyond the tree mass depends on the height and density of the trees in the barrier. Figure 3-33
A fence with openings offers maximum protection from the wind. The foliage mass of plants acts like a solid object in the landscape to direct the wind around and over itself, thereby creating a protected, calm zone on the “lee” or opposite side from the wind. In fact, gaps in the tree mass may actually increase the wind’s velocity through these areas. Some infiltration of wind helps to uplift the current that is
moving over the top of the fence. Figure 3-31
A mass of tall evergreen shrubs located next to the exterior house wall can protect the house from cold wind. When the density increases, the lack of wind through the mass permits the deflected wind to return to the ground more quickly, thus reducing the extent of the protected area. These too can be used to lift the wind above an outdoor space or away from the west and northwest walls of the house. groups, because this will create openings allowing wind to flow through (Figure 3-30). This location is most desirable for outdoor use areas in late autumn, winter, and/or early spring. Wind channeled aчмэи ■from house
Wind channeled 4o/vord house
Figure 3-28
A mass of coniferous evergreen trees protects two areas from cold wind. The smallest zone exists on the windward side of the tree mass, whereas the largest zone is on the lee side of the tree mass. In addition, vegetation can be used to screen and direct wind on the residential site. An outdoor space with a spectacular panoramic view that is intended for cool-season use is one example of a place where a glass wall would work well. There are numerous means for protecting both outdoor spaces and the house from the potentially detrimental effects of wind blowing from the westerly direction. A carefully designed and located vertical plane can ameliorate the negative aspects of the space by blocking wind and permitting the front door to be opened and closed with diminished wind infiltration. Such a space is often inhospitably dark, cool, and windy because of its orientation. A disadvantage of using coniferous vegetation to block wind is that it covers a relatively large area of ground. An alternative that requires less space is to use walls and fences to screen unwanted cold wind. To be effective, coniferous trees should be organized in a continuous band along the west and northwest edges of a site. One is to use vertical panels of canvas that are suspended between posts or poles. Tempered glass or Plexiglas panels may be desirable in locations where a view must be preserved while blocking wind. Therefore, walls or fences intended as windscreens should be designed with small openings or individual slats (louvers) that allow some wind to filter through (bottom of Figure 3-33). Based on the microclimates around a house, it is best to place outdoor use areas requiring wind protection on the east and/or southeast side of
Figure 3-27
The effect of off-site conditions on the flow of wind toward and through a site. A general rule of thumb is that the open field velocity of wind can be reduced by up to 50 percent in the leeward zone for a distance that is approximately 10 to 20 times the height of the tree mass.[7] Within this zone, the maximum wind reduction occurs within a distance that is 3 to 10 times the height of the trees and becomes less pronounced as one moves further away. This technique also reduces heating costs. Figure 3-30
Scattered coniferous evergreen trees will allow cold wind to easily move through the site toward the house.
