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  • Writer's pictureM K

Repairing a Commercial Flat Roof Leak

Once you’ve found out the cause of your commercial roof leak the next step is to perform the repairs.

While basic repairs can be performed alone its usually best to call an experienced roofer as working on a roof can be dangerous, and a professional is better suited to make the proper repairs.

The first step is to identify what type of roofing system you have.

Commercial roofs are general made of either modified bitumen, EPDM, TPO, or PVC. There are several materials that you can use to make repairs on a roof, which material you use will depend on the type of roof you have. Usually you can tell if your roof is modified bitumen or one of the others by the seams. Modified bitumen roofs have seams every 3 feet. Single ply systems like EPDM, TPO and PVC have seams every 6 feet or more.

For asphalt based roofing systems like modified bitumen, flashing cement can be used.

The most popular brand is Karnak but any brand will do.

To reinforce your repair you will use a roofing repair fabric. This will strengthen your repair and make it last longer. Flashing cement and the compatible fabric are cheap, and can be purchased in Home Depot and most hardware stores.

For EPDM, TPO and PVC roofs you can use a silicone or acrylic product. I like to use a product called Gaco Patch as it works on all roofing membranes and is a trowel grade product which means it's thicker. This allows you to use it on walls and bigger holes. However it is significantly more expensive than flashing cement. Do NOT use flashing cement on EPDM,TPO or PVC roofs as it is not compatible. It will actually damage these roof membranes.


When using Gaco Patch you will use a white polyester fabric to reinforce your repairs.

You can usually purchase Gaco Patch and the polyester fabric from a roofing supply store if they don’t carry it you can ask them what alternative products they have for repairing EPDM and TPO.

When performing the repairs the first step is to cover the area in a base coat of your repair material. Then you cut the fabric to the length needed and you embed it into your repair material. Lastly you cover up the fabric with a top coat of your repair material.

Below is a video that shows how to perform a repair using flashing cement. When doing a repair with other material like Gaco Patch the concept is the same



If you have a commercial roof leak you want repaired in New York call (844) 998-ROOF(7663). We are experts at finding and repairing flat roof leaks, located in Brooklyn, NY.


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