Roof Mounting

When installing antennas on an existing roof or penthouse, consideration
must be taken into account on how high the antenna must be with respect
to the roof surface. Obviously the ideal location is to place the antenna right
at the roof edge. However, placing the antenna at the roof edge may not be
a viable installation design either for aesthetics, local ordinances, or practical
mounting issues. When the antennas cannot be placed at the edge of the
roof, a relationship between the distance from the edge of the roof and the
antenna height exists and needs to be followed.
The basic relationship between the antenna height and the roof edge of
the building is depicted in Figure 14-7.
The previous example assumes that there are no additional obstructions
between the antenna and the roof edge. If there are obstructions between
the antenna and the roof edge, then additional height may be needed.
Examples of additional obstructions involve HVAC units and window cleaning
apparatus.
Please remember that if there is a desire to implement severe downtilt
into the design either at the present or in the future, then the height
requirements above the rooftop may need to be increased.