Building Design and Construction Handbook - Merritt - Ventech!

16.40 SECTION SIXTEEN
consideration should be given to dividing the building into more elevator groups.
In addition to improving service, the division into local and express banks has the
advantage that corridor space on the floors where there are no doors can be used
for toilets, closets, and stairs.
While the decision to include a dedicated service elevator is often market driven,
office buildings of less than 250,000 gross square feet typically ‘‘swing’’ a passenger
elevator for off-peak deliveries and moves. Buildings of up to 500,000 or 600,000
gross square feet frequently have only a single service elevator, whereas larger
buildings are provided with two or more separate service cabs. Where dedicated
service elevators are provided, at least one should be hospital shaped, with the
capability of carrying end-loaded 9-ft-long gypsum wall board. A 12-ft ceiling
allows easy movement of carpet rolls and long conduit.
16.11.3 Elevators in Single-Purpose Buildings
Elevator requirements and layouts are similar, in general, for both single-purpose
and diversified-tenancy office buildings; but several different factors should be taken
into consideration: Single-purpose buildings are occupied by one large organization.
Generally, the floors that are occupied by the clerical staff are not subdivided into
many offices; the net rentable area is about 80% of the gross area. Population
densities are higher than for general-purpose buildings. Depending on the kind of
business to be carried on, population density varies from 100 ft 2 per person for
some life-insurance companies to about 300 ft 2 per person for some attorney’s offices.
Although traffic peaks occur at the same periods as in the diversified-tenancy
type, the morning peak may be very high, unless working hours are staggered. The
maximum 5-min periods may be 13.5 to 16.0% of the population, depending on
the type of occupancy. If traffic volumes are high, occupancy of the building should
be carefully balanced against elevator requirements. Although many floors may be
connected with an eight-car elevator bank, the time wasted on elevators becomes
excessive as a result of the number of stops made during each elevator trip.
In the past, system designers specified more elevators to meet interfloor traffic
demands of single-purpose buildings. The advent of microprocessor-based controls,
however, has dramatically improved system response to complex traffic patterns.
With such controls, an elevator system designed to handle the incoming traffic rush
will also provide satisfactory service in response to interfloor traffic.
Elevator service in single-purpose buildings is frequently hobbled by location of
a cafeteria or similar high-density, facility at some level above the ground floor. If
such facilities are served by the office passenger elevators, the total elevator requirement
can increase by 15 to 20% as a result of the inefficiency introduced by
the cafeteria.
16.11.4 Elevators in Government Buildings
Municipal buildings, city halls, state office buildings, and other government office
buildings may be treated the same as single-purpose office buildings. Population
density often may be assumed as one person per 140 to 180 ft 2 of net area. The
5-min maximum peak occurs in the morning and may be as large as 16% of the
population.