Case 3

Cause of Defects

In this case, water ponding takes place at the location where the roof gradient is insufficient. Rainwater will only flow to the lowest end of the gradient and if there is no outlet to drain them away, they will be accumulated there.

The roofing contractor realized that there is a poor workmanship at the roof drop area. The membrane started to lose its adhesiveness and causes membrane to buckle. This affects the roof gradient and causes water to retain.

Drainage

Repeated incidents of water dripping into newly constructed iconic auditoriums, concert halls and stadiums due to an inefficient drainage system are constant reminders of the high price one has to pay for such negligence. The rise in the number and intensity of rainfall and the higher reliance on roofs to retain rainwater to prevent flash floods makes it even more important to ensure that the design, construction and maintenance of the drainage system are properly done at the outset of the planning/design stage.

Important criteria to consider include:
a. Meteorological aspects
i. Design rates of rainfall
ii. Intensity of a 5-minute storm
iii. Wind
iv. Thermal movements

b. Rainwater runoff
i. Catchment area
ii. Rate of runoff

c. Hydraulic of roof drainage
i. Minimum gradient
ii. Perimeter and internal drains
iii. Flow capacity of elements
iv. Gutters, leaf cover

Local codes (e.g., SS 525) shall be consulted regarding the design, material selection, construction and maintenance of the above. The figure below shows examples of choking at a drainage outlet due to the accumulation of debris, leaves, etc. Joints in exposed sheeting materials should be arranged to facilitate
the flow of water. Special attention should be paid to the design of flashings at gutters and outlets.