Roof Drainage & Slope Design Flashcards
7 cards from real RRC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Roof Drainage & Slope Design flashcards as text
What is the minimum slope recommended by NRCA for low-slope roofing systems to ensure positive drainage?
Answer: 1/4 inch per foot
NRCA recommends a minimum slope of 1/4 inch per foot (approximately 2%) for low-slope roofing systems to achieve positive drainage.
Ponding water on a low-slope roof is defined as water that remains on the surface for how long after rainfall ends?
Answer: 48 hours
The roofing industry defines ponding water as water that remains on a roof surface 48 hours or more after rainfall has ended.
Which type of roof drain is installed at the roof's low point and routes water through vertical downspouts inside the building?
Answer: Interior drain
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.
What is the primary function of an overflow drain or overflow scupper on a low-slope roof?
Answer: To serve as a backup when primary drains are blocked or overwhelmed
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.
According to IBC, the overflow drainage system must be designed to handle what flow condition?
Answer: The same flow rate as the primary drainage system, assuming primary drains are blocked
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.
What is a scupper in the context of low-slope roof drainage?
Answer: A through-wall opening in a parapet that drains water to the building exterior
A scupper is a through-wall opening in a parapet or raised curb that allows roof drainage to discharge to the exterior of the building, eliminating interior downspout routing.
Which factor most directly determines the hydraulic capacity of a roof drain?
Answer: The drain body diameter and design flow rate
A drain's hydraulic capacity is primarily governed by its bowl diameter and the corresponding design flow rate, which determines the volume of water that can be discharged per unit time.