Note: Descriptions are shown in the official language in which they were submitted.
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-- The invention is directed to a combination roof and
ceiling construction and, more particularly, to a fire rated
ceiling assembly used in conjunction with a heavily insulated
roof construction.
Description of the Prior Art
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U.S. Patent No. 3,068,535 is directed to a conventional
roof structure which utilizes a metal roof deck, a fiberboard
roofing insulation and a water-resistant outer barrier coating.
U.S. Patent No. 3,483,664 is directed to another example
of a conventional roof structure wherein the roof is provided
with a support 26, fiberboard insulation 27, and a water-
resistant outer barrier thereover.
Finally, U.S. Patent No. 3,763,614 is directed to a :
specialty roof structure wherein a gypsum board fire barrier is
placed between a roof deck 12 and a flammable foam insulation 16.
The object herein is to provide a roof aonstruction
and ceiling assembly wherein the ceiling assembly secures an
acceptable fire rating due to the limited heat buildup in the ;~
plenum area between the roof construction and suspended ceiling
assembly. The roof construction incorporates a material which
operates as a heat sink to soak up excessive heat which is
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; developed in the plenum area during a conventional fire rating
test for the suspended ceiling assembly.
Summary of the Invention -~
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The invention is directed to a conventional roof
structure which utilizes a roof support means having thereover
a metal roof deck. Positioned on the metal roof deck is a heat
sink material, such as gypsum board, which contains water of
hydration. Overtop of the heat sink there is placed fiber
- 30 insulation, and finally over this there is placed bituminous
; ~ treated felt paper to form a water-resistant barrier for the
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outside o~ the ~oof stxucture. Below the xoof support means
there is positioned a suspended ceiling assembly, and between
the suspended ceiling assembly and the roof support means there
is defined a plenum area.
Thus, in accordance with the present teachings, an
improvement is provided in a roof construction and ceiling
assembly combination when the roof construction comprises a ~,r;,.,
roof support means with a metal deck having an upper surface
and a lower surface resting on the roof support means with
a layer of thermal insulation positioned ab~ve the upper
surface of the roof deck and a water barrier above the layer
of thermal insulation forming the exterior of the roof
construction with the ceiling assembly comprising a grid
runner system suspended from the roof support means with ire
resistant ceiling boards positioned within the grid runner
system to form a fire resistant barrier with a plenum area
formed between the ceiling assembly and the roof construction.
The improvement provided in the roof construction and ceiling `
assembly combination comprises a heat sink means which is
positioned between the roof deck and the layers of thermal
insulation to absorb excess heat in the plenum area, the heat
sink means containiny water of hydration which is released at
a temperature of about 250F or higher.
In accordance with a urther embodiment an improvement
is provided in the method of securing an improved fire rating
for a combination roof construction and ceiling assembly wherein
the roof construction comprises a roof support, metal roof ~ ,
deck thereover with a layer of thermal insulation thereover and
a water barrier thereover and the ceiling assembly comprises a `~
grid runner system and fire resistant ceiling boards mounted
therein with a plenum chamber being provided between the roof
construction and ceiling assembly. The improv~ment in the method
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comprises providing a material Which acts as a heat sink with
water of hyaration which is positioned in the roof construction
between the plenum area and the layer of thermal insulation 'and utilizing the heat sink as a means ~or absorbing heat in
the plenum area to improve the fire rating characteristics of
the suspended ceiling assembly-roof construction combination. x
Brief Description o~ the Drawing
The drawing is a cross-sectional view of the invention ' -`
, herein.
Description of the Preferred Embodiments
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, A problem associated with the designing of fire- ,` :
resistant, dry construction roof constructions and ceiling assem- `
blies employin~ fire-resistant suspended membrane ceilings as ?
a fire protection membrane is that the roof insulation of the
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,"? roof construction placed over the steel deck of the roof ~;i
~ construction confines heat within the plenum area between the
'!,$~ rOOL construction and the ceiling assembly so that with a fire
qj in the room below the ceiling assembly, there is a rapid heat
-j buildup in the plenum area with the generation of excessive
'"~ 20 temperatures in the plenum area early in a conventional ASTM
E-ll9 fire-resistance test for the ceiling assembly. Typically,
~;i only 1 to 1-1/2 inches of roof insulation would normally be
'~ employed along with a conventional fire-resistant suspended ;
ceiling assembly if the usual one-hour ire-resistant test
`~, rating were desired. However, due to the current energy crisis,
an efficient energy conserving roof structure requires consider-
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'~ ably more insulation, usually between 2 inches to 6 inches,
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;1. depending upon the geographic location of the buiiding and type -
of insulation used.
~`ii' 30 The invention herein consists in the providing of a
material sandwiched between the rovf insulation and the steel
roof deck of the ceiling construction so that the material
provided will act as a heat sink, absorbing heat from the plenum
space in a manner similar to the way in which concrete
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acts as a heat sink in a typical floor and ceiling fire- ;
resistant assembly. Gypsum board, ~hich contains water of
hydration, makes a good heat sink. Indications are that a
typical gypsum board will extend the fire-resistant rating times
for as much as 45 minutes. The gypsum board is a good material
to use because of its stability and other desirable properties
at room temperaturej as well as its relatively low temperature
of dehydration (250F.-1000F.). The gypsum board further pro-
vides an advantage in that it provides a~leveling and traveling
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j 10 surface on which to mount the insulation for the roof, and
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further, the gypsum board improves the membrane strength in
the roof deck. Other materials that can be used are vermiculite-
concrete board or other low density concrete board.
Referring now to the figure of the drawing, a conven-
~ tional roof construction and ceiling assembly is shown. Con-
.;
ventional roof construction would normally be provided with
~ ~ elements l, 2, 4, and 5. Element l is a conventional water
; barrier for the exterior of the roof. It would normally be
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composed of a number o~ laye~s of bituminous roofing felt
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;~ 20 material adhered in position through the use of tar or a like
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material. Such a structure is typical in the art, as shown in
U.S. Patents No. 3,068,535 and 3,483,664.
Below the water barrier 1 there would be placed in-
sulating boards 2. ~lhese boards would normally be one or more
layers of insulating material such as inorganic mineral fibers,
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glass fibers, or similar type inorganic fiber structures. The
structures are ric~id, are fire resistant, and provide a desirable
` insulation rating to the roof structure.
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; Normally, the insulation would be supported on a con-
ventional metal corrugated or fluted roof deck 4, such as the
commerically available Robertson roof deck. ~ll this is in turn
supported on a roof support means, which would be typically a
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; metal bar joist, truss or beam structural element.
Below the roof construction, a conventional suspended `;
ceiling 6 is positioned. The ceiling is hung from the roof ;
support means S through suspension wires and a conventional metal
ceiling suspension system. The ceiling suspension system in turn
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holds fire-resistant mineral fiber ceiling boards in position.
U.S. Patent No. 3,889,435 is typical of a conventional fire- -
resistant suspended ceiling system. In the area between the roof
deck 4 and the top of the suspended ceiling system 6, there is
defined an open area which is called a ~Iplenum~. During a
typical fire test to secure a desired rating for the suspended
ceiling system 6, the temperature within the plenum area must
; be held to certain acceptable levels. With a typical roof
structure, which only employs 1 to 1-1/2 inches of roof in-
sulation, the plenum temperature during a fire test would be
,~ kept at an acceptable level. However, with the use of two or
more inches of insulation in the roof structure, the heat loss - :
~;` in the roof was cut down to the point that excessive heat
would build up within the plenum area. The provision of a heat
sink 3 with water of hydration became necessary as a means to
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absorb this excess heat in order to secure the desired fire
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;;~ rating for the suspended ceiling system. Through the use of
,;' 3/8 inch, 1/2 illch and 5/8 inch board 3 acting as a heat sink,
such as gypsum board, it was possible to improve the plenum
temperature conditions to hold them to an acceptable temperature
~ for a one-hour fire test. The gypsum board utilized need not be
,i~ the special fire resistant, fiber-containing gypsum board, but,.,.,.,,., ~
could simply be the conventional gypsum board utilized for dry-
wall constructions.
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The gypsum board had a further advantage in that it ~ -
provided strength to the rigid fiber insulation. While the s-~
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fiber insulation is rigid, it would not always support the
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weight of a workman, particularly in those areas where the fiber . :
was bridging the gaps of a corrugated roof structure. Gypsum
board now provided a ridge over the gaps of the corrugated roof
deck so that workmen can walk on the rigid fiber insulation
without having their feet pass therethrough into the corrugation
of the roof deck. ~ .
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