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  • Writer's pictureM K

Finding Commercial Flat Roof Leaks.

Updated: Jul 13, 2023

Dealing with commercial roof leaks can be challenging as the size of the building makes it hard to search for and identify the exact issue that is causing the leak.


Commercial roofs are roofs over buildings such as stores, malls, warehouses, and apartment complexes. Basically any roof that’s not zoned residential.


In this post I will discuss ways to help you identify the cause of leaks in commercial buildings, and how to address them.

The first thing you want to do when trying to solve a leak is to find out the area on the roof directly above the leak in your building. Usually this is done by mapping out the internal leaking area with a measuring tape and then measuring out to that point on top of the roof.


I like to do this by finding any point in the building that can easily be located on the roof and then measuring from that. You can do this by measuring from the closest corner of the building. Alternatively you can measure from a skylight or drainpipe that you’ll be able to locate when you are on the roof.

Once your on the roof you will use your measurements to pinpoint the leaking area. Occasionally your measurements will lead you directly to cause of the leak. Sometimes you’ll find an open seam, or a puncture directly in that area. Other times there will be a penetration such as a pipe or hvac unit in that area that is not sealed properly. If this is the case you got very lucky, and repairing that deficiency should fix your leak. But more often than not you don’t find an immediate cause of your leak directly in that area. The reason for this is that on flat roofs its common for the water to enter the roof at a higher point and then travel down between roof layers or on your roof deck (plywood, metal or concrete), before leaking out into your building. This means that any area of your roof that is higher up from the leaking point that pitches down towards that area can potentially be a suspect.

If this is the case for you and you haven’t yet found the cause of your leak the next step is to slowly work our way outward from the leaking area looking for roof deficiencies. You want to keep in mind the pitch of your roof and work upwards towards areas that slant to your leaking area. That means areas that are lower or that pitch away from your leak dont need to be checked at this point.


Things you’ll want to look for will include:

  1. Seams, especially in ponding areas where water sits = Check for areas where the seam is open

example of open seam

example of an open seam in the top left of the picture

2. Penetrations such as pipes, hvac units, pitch pockets, and skylights = check the flashing around the penetrations for cracks or unsealed areas


example of a penetration that is not sealed well along the flange

example of a penetration that is open at the base where the wire meets the roof

3. Parapet walls = inspect the coping to make sure it covers the top of the wall and has no cracks, also check the walls to make sure the roofing membrane and flashing cement are attached properly and aren't sagging off or cracking .

extreme example of roof membrane sagging off parapet wall

example of flashing on parapet wall that is cracking

4. Damage to your roof membrane such as cuts or punctures = look for holes in your roof membrane.

example of puncture in membrane

Finding the source of a leak is an extremely difficult task. While sometimes the roof deficiencies are obvious many other times they are small or difficult to find. Even proffesionals can struggle to find mysterious leaks. Having a trained eye, and knowing what to look for greatly increases your chances of finding the leak.


If you need professional help locating and repairing a commercial roof leak in NY call (844) 998-ROOF(7663)


Normally at this point after working your way out from your leaking area you will have spotted areas that you suspect can be causing or contributing to your leak. Now it's time to repair these areas and see the results. Sometimes it will take multiple searches and repair attempts before nailing the leak.


In the next post we will explain how to go about repairing your flat commercial roof.

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