Flat RCC roofs — recommended slope (fall) for drainage For a reinforced cement concrete flat roof, what is the recommended practical slope to ensure positive drainage and avoid water ponding?

Introduction / Context:
So-called “flat” roofs must, in reality, have a small slope (fall) so that rainwater drains to outlets or gutters. Without adequate fall, roofs are prone to ponding, leakage, and faster deterioration of waterproofing layers. This question checks the practical design fall for RCC flat roofs.

Given Data / Assumptions:

• Roof type: RCC slab with screed/waterproofing.
• Objective: just enough slope for drainage; not an inclined pitched roof.
• Common practice uses gradients like 1 in 40 to 1 in 60.

Concept / Approach:
Typical recommended falls translate to approximately 1.0–1.5 degrees. Designers often specify a screed to produce this slope across the roof surface, guiding water to rainwater pipes. A zero slope is unacceptable because even minor construction irregularities will trap water; 10 degrees is far steeper than necessary and impractical for walking surfaces. “200°” is nonsensical in this context.

Step-by-Step Solution:

Verification / Alternative check:
Roofing and waterproofing handbooks recommend falls in the above range to extend membrane life and avoid hydrostatic head buildup at joints.

Why Other Options Are Wrong:

• zero: leads to ponding and leakage.
• 10°: excessive for “flat” roof usage and aesthetics.
• 200°: meaningless option for slope.
• none of these: incorrect because a gentle fall is correct.

Common Pitfalls:
Assuming the slab casting will be perfectly level; neglecting screed; forgetting to coordinate falls with drain locations.

Final Answer:
a few degrees (gentle fall)