What does drainage reliability ensure in FM Global guidelines?

• A. It ensures that drainage systems prevent ponding and structural collapse from water load.
• B. It ensures faster installation.
• C. It reduces the need for drainage.
• D. It only applies to interior roofs.

Answer: (A)

Drainage reliability is about the roof drainage system keeping up with rainwater so water doesn’t pond on the roof. When ponding occurs, the roof carries extra water load, which stresses the deck, membrane, and supports and can lead to leaks or even structural problems. FM Global emphasizes reliable drainage to prevent that ponding and the associated risk of collapse from the water load.

So the best answer is that reliable drainage ensures ponding is prevented and the structure isn’t compromised by water weight. The other options don’t fit because drainage reliability isn’t about faster installation, reducing the need for drainage, or being restricted to interior roofs; it’s about consistently removing water from exterior roof surfaces under expected rainfall.