If internal drains become blocked, what is a likely consequence?

If internal drains become blocked, what is a likely consequence?

• A. Ponding on the roof surface
• B. Reduced water retention
• C. Increased drainage efficiency
• D. Decreased runoff

Answer: (A)

Blocked internal drains prevent water from leaving the roof as designed, so rainfall begins to accumulate on the surface. This leads to ponding, where a visible pool of water sits on the roof. Ponding is a real concern because it adds dead load to the roof structure, stresses the waterproofing system, and increases the risk of leaks and membrane damage over time. In cold weather it can also promote ice formation and create additional hazards. The other options don’t fit because they describe outcomes associated with better drainage or less surface water. If drains are blocked, you wouldn’t expect increased drainage efficiency or decreased runoff; instead, water remains on the roof, forming ponding rather than being quickly pumped away.

Blocked internal drains prevent water from leaving the roof as designed, so rainfall begins to accumulate on the surface. This leads to ponding, where a visible pool of water sits on the roof. Ponding is a real concern because it adds dead load to the roof structure, stresses the waterproofing system, and increases the risk of leaks and membrane damage over time. In cold weather it can also promote ice formation and create additional hazards.

The other options don’t fit because they describe outcomes associated with better drainage or less surface water. If drains are blocked, you wouldn’t expect increased drainage efficiency or decreased runoff; instead, water remains on the roof, forming ponding rather than being quickly pumped away.