Final answer:
The correct answer is that a secondary roof drain must be set at 1 inch higher than the roof surface, to serve as an emergency overflow when the primary drain is insufficient.
Step-by-step explanation:
The question pertains to the minimum requirements for the placement of a secondary roof drain relative to the roof surface. According to plumbing codes and regulations, a secondary roof drain should be set at a height that ensures it functions only when the primary drainage system is not working effectively, which is typically during a situation where the primary system is overwhelmed or blocked. Hence, the correct answer is:
b: 1" higher
This setting is to allow for the drainage of water in excess of normal levels, ensuring that there won't be ponding or excessive accumulation of water on the roof which can cause structural damage. A secondary roof drain that is 1 inch higher than the roof surface will activate when the water level on the roof exceeds the height of the primary roof drain, indicating 100% of the design flow rate of the primary system, effectively serving as an emergency overflow mechanism.