Recommendations to Avoid Sheltered Areas. If shelter is not
desired, plant trees far apart. Shade trees can be used around buildings
without too much ventilation interference if the trees are tall, the trunks
are kept bare and the trees are kept close to the building (see Figure 13).
Dense hedges should not be placed so that they affect the airflow through
Change in the Direction and Velocity of Airflow
Deflecting Airflow. Rows of trees and hedges can direct air
towards or away from a building (see Figure 13). For ventilation, it is
generally best to orient rows perpendicular to the window walls to channel
airflow towards openings, provided that solar control is maintained.
Dense hedges can be used in a manner similar to solid building
wingwalls to deflect air into the building openings. Refer to para. 4.5.3.
Vegetation may be used to create positive and negative pressure zones for
ventilation or to increase the windward area of the building. Per unit area,
vegetation will not be as efficient as solid wingwalls in producing these
effects, but it can be more cost effective than wingwalls because it can be
much larger at a lower cost.
Increasing Wind Velocities. Vegetation can create areas of higher
wind velocities by deflecting winds or by funneling air through a narrow
opening. See Figure 15 and Appendix C, para. 3.2. Narrowing the spacing of
the trees used to funnel air can increase the airflow 25 percent above that of
the upwind velocity. A similar effect occurs at the side edge of a windbreak.
Blocking Solar Radiation. Large-scale landscaping such as trees
and vines on trellises are used to shade buildings and the surrounding ground
surfaces. This reduces direct solar gain to the building and indirect
radiation reflected upward into the building from the ground. Trees can block
up to 70 percent of the direct solar radiation, and also filter and cool
surrounding air through transpiration.