Understanding Roof Ponding Water

Roof ponding water is a common issue that can lead to significant problems if not addressed promptly. It occurs when water accumulates on a flat or low-slope roof surface and remains there for more than 48 hours without draining or evaporating. This problem can lead to structural damage, deteriorate roofing materials, and create an ideal environment for mold growth. Understanding the causes, effects, and solutions for ponding water is crucial for maintaining the integrity of your roof and protecting your property.

Causes of Roof Ponding Water

Several factors contribute to the occurrence of ponding water on roofs. These include:

  • Poor Roof Design: Inadequate slope or drainage design can result in water not flowing off the roof efficiently.
  • Blocked Drains: Debris, leaves, or ice can block gutters and drains, preventing water from leaving the roof surface.
  • Structural Issues: Building settling or structural issues can create low spots on the roof where water can accumulate.
  • Roof Surface Deterioration: Over time, the roofing materials can wear out, leading to depressions where water can collect.
  • HVAC Units and Equipment: Heavy equipment placed on the roof can cause indentations and disrupt the roof’s natural drainage path.

Effects of Roof Ponding Water

The presence of standing water on a roof can have several negative impacts:

  • Membrane Degradation: Constant exposure to water can weaken the roofing membrane, leading to leaks and water infiltration.
  • Increased Load: The added weight of ponding water can strain the roof structure, potentially leading to structural damage or collapse.
  • Mold and Mildew: Pooled water provides a perfect environment for mold and mildew to thrive, posing health risks and damaging the roofing material.
  • UV Degradation: Water can magnify the effects of UV rays, accelerating the breakdown of roofing materials.
  • Roof Plant Growth: Ponding water can encourage the growth of plants and algae, which can damage the roof and interfere with drainage.

Solutions to Roof Ponding Water

Addressing roof ponding water promptly can prevent further damage and prolong the life of your roofing system. Here are some effective solutions:

Improve Roof Drainage

Ensure that your roof has an adequate slope and that drains and gutters are clear of debris. Regular maintenance can help prevent clogs and ensure efficient water flow.

Add Tapered Insulation

Installing tapered insulation can create a slope on flat roofs, guiding water towards drains and preventing puddles from forming.

Install Roof Crickets

Crickets are triangular structures designed to divert water around obstacles like chimneys or HVAC units, facilitating better drainage.

Roof Coatings

Applying reflective or waterproof coatings can protect the roof membrane from UV damage and water infiltration, making the roof more resistant to ponding water effects.

Regular Inspections and Maintenance

Conduct periodic roof inspections to identify and address potential problem areas before they escalate. Regular maintenance can extend the life of your roof and prevent water accumulation.


Roof ponding water is a serious issue that requires timely attention to prevent extensive damage and costly repairs. By understanding its causes, effects, and solutions, property owners can take proactive steps to maintain their roofs’ integrity. Regular maintenance and proper roof design are critical in ensuring effective water drainage, preserving the roof’s condition, and protecting the building’s overall structure.

Spokane Home Inspection