Building Exterior Drainage System

This factor considers the presence of primary and secondary drainage facilities to remove accumulated rain water from building roof and balconies. The arrangement and condition of drains is considered. This includes adequacy of drains to avoid pooling, maintenance of drains to avoid obstructions, and termination of drains to acceptable locations.

It is important that they are kept clear of blockages and are routinely inspected, particularly before the storm season.

Negative Positive
Primary drains provided, but no source of secondary drainage provided. Adequate primary drainage consisting of roof edge gutters and downspouts. Secondary drainage is simply overflow from the roof edge.
Primary and secondary drains provided, but debris is present, capable of obstructing drains. Adequate primary and secondary drainage systems provided for trapped rooftop or balcony areas.
Additional primary drainage needed to address ponding, or re-pitching of roof is needed to existing drains. Drain covers provided where needed. Secondary drains are often raised 5 cm (2 in) above the roof deck and not covered.
Secondary drains do not terminate to an observable location. Drains meet requirements for 100-year precipitation event.

  • Improve the condition of the primary roof drain system by cutting away roof covering material extending into the drain openings.
  • Improve the condition of the primary roof drain system by replacing missing covers that protect the drains from the entrance of debris.
  • Improve the condition of the primary roof drain system by repairing damaged or obstructed down spouts.
  • Provide secondary drains for all roof areas with parapet walls and all balconies with solid perimeter walls. Terminate secondary drains to an above grade, observable location.
  • Remove debris from rooftop areas that could become obstructions to primary and/or secondary drains.