RRC Roof Drainage & Slope Design 3

Question 1

What is a drain 'sump' in the context of roof drainage design?

Accepted Answer

A recessed area built around a roof drain to collect water and improve flow into the drain

Answer

A pump system used to remove standing water from flat roofs

Answer

A type of overflow scupper installed through a parapet wall

Answer

The lowest designated point of a drainage basin

Question 2

How is the maximum allowable tributary area served by a single roof drain determined?

Accepted Answer

By matching the drain's hydraulic capacity to the design rainfall intensity for the location

Answer

A fixed limit of 5,000 sq ft per drain regardless of conditions

Answer

A fixed limit of 10,000 sq ft for all standard roof drains

Answer

By the architect's judgment without code requirements

Question 3

When designing drainage for a large low-slope roof with multiple low points, which approach is most effective?

Accepted Answer

Multiple independent drainage basins each sloped to their own dedicated drain

Answer

A single central drain serving the entire roof area

Answer

A single perimeter gutter system collecting all runoff

Answer

Random drain placement dictated by available structural penetration locations

Question 4

What is the primary purpose of a controlled-flow (siphonic) roof drainage system?

Accepted Answer

To restrict outflow rate, allowing smaller downstream piping while temporarily storing water on the roof within structural load limits

Answer

To increase discharge speed and eliminate overflow risk during peak storms

Answer

To prevent overflow drain activation under all design storm conditions

Answer

To filter debris before water enters the interior plumbing system

Question 5

What term describes the roof surface area that contributes runoff to a single drain?

Accepted Answer

Tributary area

Answer

Catchment basin

Answer

Runoff zone

Answer

Collection field

Question 6

Which flashing component at the base of a parapet wall is most critical for preventing water infiltration beneath the roof membrane termination?

Accepted Answer

Base flashing

Answer

Counter flashing

Answer

Coping cap

Answer

Through-wall flashing

Question 7

In roof drainage design, what does the term 'hydraulic gradient' refer to?

Accepted Answer

The slope of the energy line in a drainage pipe, which governs flow velocity and capacity

Answer

The material density variation in drain pipe walls

Answer

The ratio of roof slope to drain opening size

Answer

The percentage of total rainfall that becomes surface runoff