What NYC Property Owners Need to Know About Flat Roofs, Terraces and Mold

By Robert Weitz, Principal, RTK Environmental

After more than 30 years of inspecting homes and buildings, one thing I’ve learned is that water rarely stays where you expect it to.
That’s especially true in New York City, where flat roofs, rooftop terraces, penthouses, and brownstones are common. After heavy rain, a small drainage or roof problem can turn into water intrusion inside walls, ceilings and apartments below.

And once moisture gets into building materials, mold can follow.

Why Flat Roofs Can Create Problems

Flat roofs are everywhere in New York City. Over time, they can deteriorate or sag. If water isn’t draining properly, it can start to collect.
Water looks for the weakest point of entry. Once it gets through the roof, it can move into ceilings, walls, and other parts of the building. What makes these situations difficult is that the place where you see the damage isn’t always where the water actually came in.
A stain on the ceiling may be the first visible sign, but the moisture could have traveled much farther before you noticed it.

Rooftop Terraces Need Attention, Too

Rooftop terraces present a different kind of risk.
A drain clogged with leaves or debris can keep water from moving off the terrace the way it should. Once that happens, water starts looking for another path.

Sometimes that path is into the building.

For penthouse owners and residents living directly below a terrace, a leak or ceiling stain shouldn’t automatically be treated as a minor cosmetic issue. The bigger question is: where did the water go?

That’s the question I would want answered.

Brownstones Have Their Own Vulnerabilities

Brownstones and row houses aren’t immune to these problems.
Roof leaks are one concern, but water can also enter through deteriorated pointing around brick and windows. Once moisture gets into an exterior wall, it can remain there before any obvious sign appears inside the home.
This is where property owners can get into trouble. They fix the visible leak, repaint the wall, and assume the issue is over.
But was everything behind that surface actually dry? If not, the problem may still be there.

When Water Intrusion Becomes a Mold Concern

Mold can begin growing within 24 to 48 hours after water exposure if wet materials aren’t dried quickly.
The challenge is that you may not see it. Mold can develop behind walls, above ceilings and beneath flooring. A musty odor, condensation, peeling paint or wallpaper, or damage to wood can signal excess moisture.
That’s why repairing the source of a leak is only part of the job. You also need to understand where the water traveled and whether the affected materials were completely dried.

Property Owner Action Checklist

After heavy rain or a known roof or terrace leak:

• Check roof and terrace drains. Remove leaves and debris that can prevent water from draining.
• Look for standing water. Water that remains on a roof or terrace can signal a drainage problem.
• Check the areas below. Look at ceilings and walls for staining, bubbling or peeling paint and other evidence of moisture.
• Pay attention to musty odors. They can be a sign of a moisture or mold problem that isn’t visible.
• Don’t stop at the obvious damage. Water can travel through ceilings, walls and floors before you see evidence of it.
• Make sure wet materials are completely dried. Time matters because mold can begin growing within 24 to 48 hours after water exposure.
• Investigate recurring leaks or stains. Repainting a damaged area doesn’t address moisture that may still be behind it.
• Consider an independent inspection when warranted. If you see mold, smell a persistent musty odor or have concerns about where water traveled; testing can help determine the extent of the problem.

Why Independent Mold Testing Matters

I’ve always believed the company telling you whether you have a mold problem shouldn’t be the same company that stands to make money fixing it.
RTK performs environmental testing and inspections. We don’t perform remediation.
The purpose of an inspection is to determine whether mold is present, where it is located, how extensive the problem is, and what needs to be addressed. After remediation, clearance testing can also help determine whether the work was successful.
After decades of inspecting buildings, the advice I give property owners is simple: when water gets into a building, don’t just fix where it came from. Find out where it went.
If you’ve had a roof or terrace leak in your NYC brownstone, penthouse, apartment or building and are concerned about hidden moisture or mold, RTK Environmental can provide independent mold inspection and testing.