Dimensions of the Obstructions. The dimensions of the obstructions
affect the size and extent of the wake zones. In general, the larger and
taller the obstruction, the longer the wake. The spacing between the
obstructions determines whether the leeward obstruction will be within the
recirculating wake of the upwind obstruction. As described in para. 188.8.131.52,
a minimum clear spacing of five heights of the upwind obstruction is required.
Homogeneity or Variability of Building Height. Placing a highrise
building in an area of low-rise development may create strong air currents at
ground level (refer to Appendix A). If the upwind building is higher than the
downwind one, the lee roller of the highrise may sufficiently engulf the
downwind building to cause ventilation in the downwind building to reverse
direction (see Figure 8c).
If the building is taller than six stories, a wind tunnel test
is required to determine the pedestrian-level winds (refer to Wind Tunnel
Testing, para. 1.3 in Appendix C).
Orientation of Streets with Regard to Prevailing Winds. If streets
are laid out parallel to the prevailing winds, the wind will be funneled into
the streets. This funneling will be more pronounced if no major gaps occur
between the buildings lining the streets. If streets are laid perpendicular