Ponding water is one of the most common and overlooked threats to commercial flat roofs. While it may seem harmless at first, standing water can cause significant long-term damage if left unaddressed. In this blog, we’ll explain what causes ponding, why it’s a serious issue, and what steps you can take to prevent it—especially during the summer months.
- What Is Ponding Water?
Ponding refers to water that remains on a flat roof for more than 48 hours after a rainfall or HVAC runoff. Unlike sloped roofs, flat roofs are more prone to drainage issues. Even slight dips in the surface can collect water over time, especially if the drainage system is obstructed or improperly designed.
- Why Ponding Is a Serious Problem
Standing water may not seem urgent, but over time, it can lead to several major issues:
- Premature membrane failure: Prolonged exposure to water can degrade roofing materials, especially in high-heat conditions.
- Increased roof weight load: Water adds unnecessary stress to your building’s structure, especially after repeated storms.
- Algae and vegetation growth: Stagnant water promotes the growth of moss and algae, which can break down roofing surfaces and clog drains.
- Leaks and interior damage: As ponding water penetrates weak spots, it can cause leaks, ceiling stains, and even structural damage.
- What Causes Ponding?
There are several common causes of ponding water on commercial roofs:
- Improper roof slope or design
- Clogged or undersized roof drains and scuppers
- Debris buildup from trees, wind, or birds
- Aging roof systems with sagging or soft spots
- HVAC or mechanical unit discharge pooling near equipment
- How to Prevent Ponding Water
Preventing ponding starts with proactive maintenance and proper roof design. Here are a few effective steps:
- Regular drain cleaning: Ensure all gutters, drains, and downspouts are clear of debris year-round.
- Roof inspections: Identify and repair low spots or areas with improper slope before they worsen.
- Add tapered insulation: Tapered systems help redirect water to drainage points without altering roof height drastically.
- Install additional drains or scuppers: In high-risk areas, more drainage points can reduce standing water quickly.
- Recoat or resurface deteriorated areas: Coatings can restore slope and waterproof performance in aging roofs.
Conclusion
Ponding water may be easy to ignore—but the longer it’s left untreated, the more damage it can cause. Summer is the ideal time to assess and resolve these issues before heat and storms make them worse. At MJT Roofing, we specialize in flat roof inspections, repairs, and drainage solutions tailored to your building’s needs.
