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TECHNICAL & RESEARCH
Continued from page 14
The third option—a combination of structural steel and 
tapered insulation—is optimal. Primary drainage is 
accomplished by slope in the structure. Tapered polyiso 
crickets, with a slope of 1/2-inch per foot, supplement this 
by providing lateral movement to the drains and around 
projections.
Follow the 50 Percent Rule
The wider a cricket is, the faster water will flow to the 
drains or scuppers. Full diamonds should be used in the 
center of the roof and half diamonds used against walls. 
Following the “50 Percent Rule” ensures the cricket is 
properly sized to provide sufficient drainage. It directs 
that the half cricket—the distance from the center of the 
diamond or half diamond to a corner—should be half the 
distance between the drains or scuppers; for example, if 
the drains or scuppers are 24 feet apart, the half cricket 
should be 12 feet.
Proactively Prevent Obstructions
Roof penetrations in valley lines obstruct the flow of water to drains, 
creating landscapes ripe for ponding water. A simple proactive step, 
taken during the design process, can prevent these obstructions 
and the change orders needed to correct them… change orders 
that can cost many times more to implement than if the roof was 
designed properly in the first place. 
Computer-aided design tools can be used to overlay the framing, 
electrical, HVAC and mechanical plans onto the roofing plans. 
Obstructions can then be identified and addressed by moving 
the projections (the ideal remedy) or by elevating the curbs and 
specifying additional and opposing crickets.
Continued on page 16

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