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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

  1. What is a 'cricket' or 'saddle' used for in roof design?

    Answer: A peaked diverter built on the high side of a penetration to redirect water around it

    A cricket (or saddle) is a peaked construction built on the upslope side of a chimney, skylight, or other large penetration to divert water around the obstruction and prevent ponding behind it.

  2. At what height above the roof surface is the inlet of an overflow drain typically set?

    Answer: 2 inches above the roof surface

    Overflow drain inlets are set 2 inches above the roof surface so they only activate when primary drains are overwhelmed and water depth exceeds this threshold.

  3. What is the primary design purpose of a tapered insulation system on a low-slope roof?

    Answer: To create positive drainage slope on a structurally flat deck

    Tapered insulation systems vary in thickness across the roof to create positive drainage slope toward drains on decks that are structurally flat or have insufficient built-in slope.

  4. The design rainfall intensity used for roof drainage calculations is typically derived from which data source?

    Answer: NOAA precipitation frequency data (Atlas 14)

    Roof drainage calculations use NOAA's precipitation frequency data (Atlas 14) to determine design rainfall intensity for the specific geographic location of the project.

  5. What is the standard formula for calculating required roof drain flow rate (Q in GPM)?

    Answer: Q = A × I / 96.23 (A=sq ft, I=in/hr)

    The formula Q = A × I / 96.23 converts roof area (sq ft) and rainfall intensity (in/hr) into required flow rate in gallons per minute for drain sizing.

  6. What is the most serious consequence of chronic ponding water on a built-up or modified bitumen roof membrane?

    Answer: Accelerated membrane deterioration, blistering, biological growth, and potential structural overload

    Chronic ponding accelerates membrane degradation through thermal cycling, biological growth, and chemical attack, while also imposing sustained structural loads that may exceed the design capacity of the building.

  7. A roof with a 20,000 sq ft drainage basin and a design rainfall intensity of 4 in/hr requires a minimum drain capacity of approximately how many GPM?

    Answer: 832 GPM

    Using Q = A × I / 96.23: Q = 20,000 × 4 / 96.23 ≈ 832 GPM, demonstrating how large roof areas with high rainfall intensity require substantial drain capacity.