=15. Freight Elevators.=—Freight elevators are either corner-guided
or side-guided, the preference being for the latter, as they are
more easily constructed and adjusted, and during the construction of
the elevator shaft it is usual to build into the brickwork blocks of
wood about the thickness of a brick and of sufficient length for the
attachment of the guides. These are cut wedge-shaped on the ends, so
as to hold more firmly in the brickwork. A diagrammatic plan of a
side-guided and corner-guided elevator is illustrated in Fig. 4 (_a_)
and (_b_), respectively.
Owing to the fact that it is necessary to have considerable hoisting
mechanism, at the head of the elevator shaft, the shaft is extended
above the roof, sometimes as much as 5 or 6 feet, for the minimum
height from the elevator platform at the top floor level to the under
side of the beams carrying the mechanism is about 16 feet, and the
sheaves carrying the rope and other mechanism at the top of the shaft
require several more feet.
=16. Elevator-Shaft Windows.=—Frequently, elevator shafts are lighted
with windows. Where such windows open into the building, they must be
constructed with metallic frame and wire glass; but where they open
outside of the building it is not necessary to do this. Where elevator
shafts are lighted from the top, metallic skylights glazed with heavy
glass should be provided. It is not considered such good practice to
use wired glass for this glazing, the idea being that in case of fire,
as each floor is cut off from the elevator shaft with fireproof doors,
vent may be had from the skylight at the top of the shaft when the
glass is broken, and some of the municipal and state laws stipulate
that the skylight at the top of an elevator shaft shall not be less
than two-thirds the area of the shaft.
As there is some mechanism on the bottom of the elevator platform and
at the foot of the shaft, it is necessary to sink the shaft at least 3
feet below the basement floor level, provided that the elevator runs to
the basement floor.