How to Find Leaks on a Commercial Modified Bitumen Flat Roof


If your commercial building with a modified bitumen flat roof is leaking water into your office or warehouse space, then it is important to figure out exactly where it is leaking. Not only do you need to find the leak to stop the annoying drips and put your buckets away, but also because leaking roofing materials are very dangerous for the underlying structure of the building.

Finding a leak on modified bitumen flat roof isn't always as simple as just climbing up and looking for wet spots. Once water gets underneath the rubberized bitumen material, it can run along the underlying plywood. This makes the source of the leaking challenging to find.

To find the source of the leak on your commercial building's roof, follow this procedure:

Use Measurements to Correlate the Indoor Leaking Spot with Its Corresponding Location on the Roof

Even though the source of your roof's leak may not actually be located directly above where the ceiling is dripping water, you absolutely need to look at that area of the roof first. To do so, use a window along the nearest wall as a landmark and measure the distance from the wall to the leak's location.

Climb up on the roof, then use the measurement to find the corresponding location on the roof. Walk around the area and see if you see any of the telltale signs of water intrusion, such as:

  • Bubbles
  • Cracks
  • Dark-colored spots
  • Spongey areas

It is also important to check areas near seams in the roofing material, next to roof-mounted air conditioners, and all other structures located on the roof because these are common leaking points.

Cut the Modified Bitumen and Inspect the Underlying Plywood for Moisture

If you don't see an obvious leak, then you need to get a look at the plywood under the modified bitumen material. The best way to do so is to cut out small triangles and feel the plywood underneath to see if it is wet. 

Using the area you located in the last step, start cutting pieces of the roofing material every few feet until you have nailed down the leaking area.

Once you have located the leak and are patched it with sealant, you should patch each of the test areas as well. 

Don't Discount the Possibility of Leaking Plumbing or Fire Sprinklers

Finally, it is important to note that if your building has overhead fire sprinklers or plumbing, then it is always possible one of those is leaking instead of the roof. So, if you walk the roof, cut some test areas, and still don't see any signs of water intrusion under the modified bitumen, then you should contact a plumber and have them inspect your plumbing and sprinkler system.

If none of the above tips help, you can always contact a roof repair company like The Roof Doctor.


9 November 2018

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