RRC Roof Drainage & Slope Design

Question 1

What is the minimum slope recommended by NRCA for low-slope roofing systems to ensure positive drainage?

Accepted Answer

1/4 inch per foot

Answer

NRCA recommends a minimum slope of 1/4 inch per foot (approximately 2%) for low-slope roofing systems to achieve positive drainage.

Question 2

Ponding water on a low-slope roof is defined as water that remains on the surface for how long after rainfall ends?

Accepted Answer

48 hours

Answer

The roofing industry defines ponding water as water that remains on a roof surface 48 hours or more after rainfall has ended.

Question 3

Which type of roof drain is installed at the roof's low point and routes water through vertical downspouts inside the building?

Accepted Answer

Interior drain

Answer

Interior drains are installed at low points on the roof and connect to vertical rainwater leaders routed through the building interior to the storm sewer.

Question 4

What is the primary function of an overflow drain or overflow scupper on a low-slope roof?

Accepted Answer

To serve as a backup when primary drains are blocked or overwhelmed

Answer

Overflow drains are secondary emergency drainage devices that activate when primary drains are blocked or exceed capacity, preventing water accumulation from surpassing the structural design load.

Question 5

According to IBC, the overflow drainage system must be designed to handle what flow condition?

Accepted Answer

The same flow rate as the primary drainage system, assuming primary drains are blocked

Answer

IBC requires overflow drainage systems to be sized for the same design rainfall intensity as the primary system, calculated assuming all primary drains are completely blocked.

RRC - Registered Roof Consultant Practice Test

RRC - Registered Roof Consultant Practice Test

RRC Roof Drainage & Slope Design