320
Ceiling: Generic Design Options
322
GENERIC DESIGN OPTIONS
There are several groups of products which meet the requirements of the
basic design. Where performance of any two groups is equivalent,
preference will be given to lowest cost, both direct and indirect. Indirect
costs result from the greater depth and/or weight of one product as
compared with another, and from any added costs incurred through
construction scheduling considerations.
322.1
PLATFORM
The platform closely resembles conventional roof deck systems in many of
its performance requirements. Generic design options which generally
meet the performance criteria for the platform include the materials and/or
assemblies listed below.
322.1.1
Poured Reinforced Gypsum on Steel Tees (Figure 320-3)
1. Advantages and Disadvantages. Of the various firerated roof-ceiling or
roof deck systems presently available, poured reinforced gypsum
appears to be the most appropriate. It is the least costly of the generic
design options. It is light in weight, and it is easily cut and patched. In
typical roof decks, when holes are made within the 32" tee spacing, no
reinforcing is necessary, and when holes are repaired the deck is
restored to full strength. It has ICBO approved diaphragm shear
values over 1,000 plf and UL two-hour fire rating. (For further
discussion of fire safety, see Section 326.)
The main disadvantage of this option is that, although the gypsum
deck is strong enough to be walked on and used as a working platform
an hour or less after it is poured, it will not dry out completely for at
least thirty days under favorable conditions and as much as sixty to
ninety days under unfavorable conditions. This need not present a
scheduling problem unless it is essential for a finished ceiling to be
applied soon after the deck is poured, which is unlikely. If it is
necessary to apply the finished ceiling before the deck has thoroughly
dried out, there should be no problem if the top surface of the platform
is left unsealed and free to dry out from the top. If scheduling permits,
a breather type hardener may be applied immediately to the top
surface of the gypsum to prevent dusting and increase the wear
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