Ask an Expert: Pooling Water on Low-Slope Roofs

Ask An Expert is a question-and-answer column designed to address common questions related to forensic investigation and property damage. Each month we’ll feature one or two questions submitted by you – our readers and customers – and provide detailed, easy-to-understand answers. Email your questions to [email protected] or submit your questions here.

Question #1: Is there a rule/standard that if water ponds for a certain period of time, then the roof can’t be repaired and must be replaced?

Chris Scallion, P.E.: No such guideline exists.  Ideally, all low-slope roof products should provide positive drainage and prevent ponding water.  With relatively low slopes, small areas of relatively shallow water may accumulate after a rainstorm.  These areas should be dry within 24 to 48 hours.  Most manufacturers have guidelines regarding the period of acceptable ponding water for warranty purposes, typically 48 hours.  Localized repairs subjected to ponding water may not be eligible for manufacturer’s warranties, but spot repairs are seldom covered beyond an installer’s warranty.  Ponding water is indicative of an underlying deficiency in the construction of the roof system and should be remedied during the next roof replacement.


Question #2: I looked at an EPDM roof where it received substantial hail impact (large and large quantity).  At numerous locations, the EPDM had de-bonded from the insulation at the impact locations.  What percentage of de-bonding is acceptable before the wind rating is affected to a point where replacement is warranted?

Chris Scallion, P.E.: Any areas of loose membrane will be more susceptible to wind uplift.  Judgement would need to be made after a field investigation, but it is probable that replacement would be warranted based on the above description.  The roofing manufacturer should also be consulted.  Manufacturers should be able to qualify tolerances of de-bonded surfaces that would meet the required wind resistance based on product testing.

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About the Expert
Chris Scallion joined Donan in 2012 as a forensic engineer based out of the firm’s Raleigh, North Carolina office. Mr. Scallion has worked in structural design, building envelope science and roofing. His areas of expertise include but are not limited to flood damage, construction defects and steep and low slope roof systems. Mr. Scallion’s other project capabilities include commercial and residential roofing, flood and hurricane damage, wind and tornado damage, water intrusion, crawlspace moisture, construction defects, structural and foundation failures. View Chris’s full professional profile here.

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