A roof’s drainage system includes the gutters, leaders, drain openings and scuppers, as well as the slope provided by the structural deck, tapered insulation, crickets and sumps. The primary function of the drainage systems is to prevent the retention of water on the roof by removing water from the roof as quickly as possible. Every roof, including so-called “dead-level” roofs, must have some provision for drainage. Further, it is important that the drainage system be kept free from debris that might interfere with the proper flow of surface water.
Many roof problems can be traced directly to inadequately designed or improperly installed drainage systems; for example, the use of only one drain; the failure to install overflow scuppers in parapet walls; the placement of drains next to support columns instead of at points of maximum deflection; loose or missing drain clamping rings. Ponded water is the principal indication of inadequate drainage, and may indicate the presence of structural defects.