720
Design Rationale: Ceiling
722.1.2
Horizontal Access
By increasing the space for services sufficiently to enable maintenance
and repairs to be done above the ceiling, all the disadvantages of access
from below are resolved. The additional space means better organization
of services. The primary disadvantage is the added cost of the increase in
floor-to-floor height.
Horizontal access can be achieved by means of catwalks, or by making
the whole ceiling capable of supporting the live load of people and
materials. The latter option was selected because catwalks require
services to be organized so that all controls, etc., are grouped within reach
of the catwalk. This is often difficult and also increases the cost of
services. The density of services precludes the use of movable catwalks.
722.2
THE PLATFORM MUST BE ONE-HOUR RATED
In order to facilitate change, partitions may not penetrate the platform.
Except for two-hour fire barriers, all partitions stop at the ceiling-platform,
including one-hour smokestop partitions. The ceiling-platform, therefore,
must also be one-hour rated and smoketight. (See discussion in Section
326.)
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