|
|
PERLITE INSULATING CONCRETE ROOFDECKS
Perlite insulating concrete roofdecks offer architects, contractors and building
owners several important benefits which include:
|
| 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 (50.8mm) 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 at the bottom of this page 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 ¾ inch (19.1 mm) furring channels wire-tied to the lower chord
of the joists. The accompanying sketch details this typical design.
|
| LIGHTWEIGHT Perlite insulating concrete is light in weight, ranging from about 20-40 lb/ft³ (320-640 kg/m³) depending on the desired density and insulating value. Because of its light weight, there can be economics in the design of the structure. Typical density is 27 lb/ft³ (432 kg/m³). |
| SLOPE TO DRAIN Standing water on 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 may be mixed on-site and pumped or lifted by crane to the roof level. Once placed, it is simply screeded to the desired 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 weather. When reroofing, the existing roof insulation should be inspected for soundness and moisture content. Particular attention should be payed 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 that drainage be provided by sloping the perlite concrete. Contact Silbrico technical sales for additional information. |
