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MOLD ALERT! Navigating the Challenges of Flat Roofs and Water Damming in New York City

In the bustling urban landscape of New York City, the skyline is dotted with an architectural feature as common as it is practical: flat roofs. Common, because they appear on residential as well as commercial buildings; practical because they are more durable, cost-effective, and offer additional space for amenities like rooftop gardens and HVAC systems than alternative styles.

To clarify, flat roofs are not entirely flat; there’s a slight pitch to facilitate drainage. That said, while the style offers various advantages, their flat surfaces also bring a unique set of challenges, especially now, when NYC is experiencing record rainfall and other harsh weather conditions wrought by climate change.

The Problem of Water Damming

One of the most significant issues with flat roof construction is that it often leads to water damming, a condition that occurs when water pools on the roof and is unable to drain properly. This is particularly problematic in NYC, where heavy rains are accelerating, and snowfall is common. Factors like clogged drainage and inadequate slope contribute to the problem, all of which leads to excess water accumulating on the roof surface.

Consequences of Water Damming

The impact of water damming can range from minor inconveniences to severe structural damage. But even more important, the water can leak into the interior of the building and lead to mold growth, which can grow within 24-48 hours, and can lead to health problems for building occupants, roof material deterioration, and in extreme cases, roof collapse.

Mold exposure can lead to a spectrum of issues, particularly for those with allergies or compromised immune systems. Symptoms can range from mild allergic reactions, like sneezing and skin irritation, to more severe respiratory problems, such as asthma exacerbation and lung infections. Structurally, mold damages buildings by weakening materials like wood and drywall, leading to costly repairs. It thrives in damp conditions, causing decay and surface damage such as peeling paint.

Prevention and Solutions

Preventing water damming primarily involves regular roof maintenance. This includes cleaning gutters and drains, removing debris, and ensuring the roof’s pitch is adequate for water runoff. Technological advancements have also introduced solutions like improved drainage systems and innovative materials that reduce the likelihood of water accumulation. Regular professional inspections are crucial in identifying potential risks and addressing them in a timely fashion.

Legal and Insurance Implications

In NYC, building codes mandate regular maintenance and inspection of roofs. Failing to adhere to these regulations can result in legal liabilities, especially if neglect leads to damage or accidents. Furthermore, insurance policies may not cover damages caused by negligence, making regular maintenance not just a legal requirement but also a financial imperative.


Flat roofs in NYC, while functional and aesthetic, require a keen eye for maintenance, especially concerning water damming. Understanding the issue, its potential consequences, and the measures to prevent it are essential for every building owner and manager. Proactive measures, rather than reactive responses, are key in navigating these challenges.

If you think you might have water damage and mold, schedule a test with RTK.

A CDC study found that genetic material from the coronavirus remained on surfaces aboard the Diamond Princess cruise ship as long as 17 days. (USA Today, CDC)

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