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

1/8 inch per foot

Answer

1/2 inch per foot

Answer

3/4 inch per foot

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

12 hours

Answer

24 hours

Answer

72 hours

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

Scupper

Answer

Overflow drain

Answer

Conductor head

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

To accelerate normal rainfall drainage

Answer

To eliminate the need for primary interior drains

Answer

To prevent debris from entering primary drains

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

50% of the primary system design flow

Answer

Twice the primary drainage flow rate

Answer

Only the 100-year storm event flow rate

Question 6

What is a scupper in the context of low-slope roof drainage?

Accepted Answer

A through-wall opening in a parapet that drains water to the building exterior

Answer

A recessed area around a roof drain to improve flow

Answer

A vertical downspout inside the building

Answer

A debris screen placed over an interior drain

Question 7

Which factor most directly determines the hydraulic capacity of a roof drain?

Accepted Answer

The drain body diameter and design flow rate

Answer

The material composition of the drain body

Answer

The color and finish of the drain strainer

Answer

The height of the surrounding parapet wall