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Ponding or standing water can cause problems for both asphalt and single-ply roofing systems. Because asphalt compounds are not inherently resistant to the sun's rays, most modified bitumen and built-up roofing membranes use either a layer of factory-applied granules, a fieldapplied liquid coating or a layer of roofing gravel to protect the membrane from ultraviolet degradation. Under constant exposure to standing water, however, granule and gravel coatings will tend to wash off and liquid coatings may blister and peel. Once this important coating is removed, the underlying asphalt membrane will begin to degrade due to direct exposure to sunlight. Although single-ply roof membranes provide excellent resistance to water and sunlight, the potential for damage to the roof is also significant when water is allowed to stand on a roof.

A small cut or puncture in the roof membrane may cause little damage on a well-drained roof surface, but the same puncture located in an impacted drainage area can produce extensive damage to the roof insulation, roof deck and building contents. Although effective roof drainage can be achieved through a variety of methods, all roofs should be designed and maintained to provide a consistent and effective path for water to completely drain off and away from the roof surface within 24 to 48 hours of a rain storm. Effective drainage must also accommodate build-ups of snow and ice that may typically occur during winter months.


  • Mid-Span of Roof Beams and Joists. Because most horizontal structural members deflect in the center of the span, ponded areas are located frequently along the mid-span of these framing members.  
  • Large Rooftop Units. Heavy rooftop units can frequently cause deck deflection and create a ponding area around the unit.  
  • Roof Drainage Components.


  • roof drains - INTERNAL
  • wall scuppers
  • gutters & downspouts. 


Although improper roof drainage can best be observed immediately after a rain storm, most impacted drainage conditions will leave "tell-tale" indications even after standing water has evaporated:

  • Accumulated Debris. Debris frequently accumulates in ponding areas. Because water eventually evaporates from impacted areas, a concentric pattern of debris or dirt is a good indication of a ponding condition.  
  • Visible Sagging or Deflection.
  • Discoloration of Curbs and Walls. The discoloration may be due to a build-up of snow or ice, or it may be an indication that water may "back up" during very severe rain storms.
  • Damage to Drainage Components. Please refer to Item E - "Inspecting For Moisture Infiltration"


  • Remove Debris. Bag and remove from the roof.  
  • Repair Drainage Components. Please refer to "Inspecting Roof Sealants and Sheet Metal." 


  • Add Roof Drains. Roof drains can be added to remove water from impacted areas.
  • Add Taper Systems. Water in impacted areas can be diverted by adding tapered "saddles" and "crickets".
  • Redundant Membrane Layer. If it is not economically possible to re-work an impacted drainage area, the potential for damage can be reduced by the application of redundant layer of membrane and flashing, in order to reduce the possibility of cutting or puncture.
  • Sumping the drains to a lower profile 4’x4’ will help evacuate standing water.



All Roof Edmonton is Edmontons Number One Choice When It Comes To Your Roof, Roof Repairs and Roof Maintenance. Residential or Commercial All Roof Edmonton Has You Covered.


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