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What is Perlite?
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- Typical Perlite Insulating Concrete Roofdeck Design
"U"
Values- Perlite Concrete Roof Slabs
Typical Concrete Weight Comparisons
Physical Properties and Mix
Proportions for Perlite Concrete
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Insulating Concrete Roofdecks
Perlite Insulating Concrete Roof Decks
Perlite insulating concrete roofdecks offer architects, contractors
and building owners several important benefits which include:
- Excellent Insulating Values
- Excellent Fire Ratings
- Lightweight
- Slope to Drain
- Monolithic Roofing Base
INSULATING VALUES
Insulating values of a perlite concrete roofdeck depends on the density of the concrete
mix that is prepared. Typical U values range from 0.21 Btu/h*ft2*F (1.19
W/m2*K) for a 2 inch (50.8 mm) 27 lb/ft3 (432 kg/m3) to
0.12 Btu/h*ft2*F (0.6 W/m2*K) for a 4 inch (101.6 mm) thick
roofdeck. The table included on the side menu bar provides a range of typical insulating
values.
FIRE RATINGS
There are a number of different perlite concrete roofdeck designs that offer fire ratings
of from 1 hour to 3 hours. A typical 3 hour rated roofdeck design consists of 2 inch (50.8
mm) minimum thickness of perlite concrete on 28 gauge galvanized corrugated steel
supported by steel joists 4 feet (1.22 m) on-center. Ceilings of 7/8 inch (22.2 mm)
perlite gypsum plaster on expanded metal lath that is attached to 3/4 inch (19.1 mm)
furring channels wire-tied to the lower chord of the joists.
LIGHTWEIGHT
Perlite insulating concrete is light in weight, ranging from 20-40 lb/ft3
(320-640 kg/m3) depending on the desired density and insulating value. Because
of its lightweight, there can be economies in the design of the structure. Typical density
is 27 lb/ft3 (432 kg/m3).
SLOPE TO DRAIN
Standing water on a roofdeck is destructive to roofing membranes. Perlite concrete may be
easily sloped to drain to internal drains or to the roof edge. Perlite concrete may be
provided by transit mix or it may be mixed on-site and pumped or lifted by crane to the
roof level. Once placed, it is simply screened to the desire thickness and slope.
EXCELLENT ROOFING AND REROOFING BASE
Perlite concrete roofdecks offer several important benefits in roofing. As perlite
concrete roofdecks are seamless, they provide a monolithic base for roofing that is smooth
and even. In addition, roofing membranes may be adhered directly to the perlite concrete
roofdeck or base sheets for built-up roofing may be nailed directly to the perlite
concrete using one of several different design fasteners. Roofing can be applied as
soon as the perlite insulating concrete can carry construction traffic and is sufficiently
dry to develop adhesion with hot asphalt or pitch. Under normal conditions, this is
about three days. Time will vary depending on the weather.
When reroofing, the existing roof insulation should be inspected for soundness and
moisture content. Particular attention should be paid to the support structure to
determine if it is capable of safely supporting new roof loads. All loose gravel and dirt
should be swept off the existing roof. For optimum roofing performance, it is recommended
the drainage be provided by sloping the perlite concrete.
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