What is the correct size of a downspout for a rainfall intensity of 100 mm if the deck roof area is 435 mm2?

To determine the appropriate size of a downspout for the specified rainfall intensity and roof area, we must consider how much water will flow through the downspout during peak rainfall conditions.

The first key factor is the given rainfall intensity, which is 100 mm. This value represents the depth of water that accumulates over a one-hour period. The deck roof area is mentioned to be 435 mm², which is the area from which rainwater will be collected.

To find the volume of water that falls on the roof during the peak rainfall, you can multiply the rainfall intensity by the roof area. This will give us the total volume of water that needs to be drained away.

Since the intensity is in millimeters and the area is in square millimeters, you'll need to ensure your units match appropriately when calculating flow rates and downspout size.

The correct answer suggests a downspout size of 100 mm, representing a balance between ensuring sufficient capacity to handle the volume of water from the roof area during the intense rainfall and the physical size of the downspout itself. A downspout with a diameter of 100 mm is generally able to handle higher volumes of water efficiently given the parameters of the question.

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