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 drain sump is a recessed depression built around a roof drain that improves drainage efficiency by collecting water and directing it into the drain, particularly important on nearly flat roofs.

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

Maximum tributary area per drain is determined by matching the drain's hydraulic flow capacity against the geographic design rainfall intensity, following plumbing 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

Dividing a large roof into multiple independent drainage basins, each with its own dedicated drain, provides redundancy and ensures localized drain failure does not affect the entire roof.

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

Controlled-flow systems restrict peak discharge to reduce downstream pipe sizing requirements, trading temporary on-roof water storage (within structural limits) for reduced plumbing infrastructure costs.

Question 5

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

Accepted Answer

Tributary area

Answer

The tributary area is the portion of roof surface that drains to a single point, and it is the primary variable — combined with rainfall intensity — used to calculate required drain capacity.

RRC - Registered Roof Consultant Practice Test

RRC - Registered Roof Consultant Practice Test

RRC Roof Drainage & Slope Design 3