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How to Repair a Flat Roof Leak

If you have a roof of any kind, then chances are that you are going to be repairing leaks sometime in the future.

The good news though, is that if you know what to look for, you can save yourself a lot of money by repairing the roof leak before it becomes too extensive. Crumbling sheetrock, electrical system damage, mold growth, and destroyed belongings are just a few problems that a leaky roof can cause, and addressing leaks early is important for preventing the damage from becoming worse.

Before you get started repairing your flat roof, you should determine how long ago the roof was installed. If it is a recent installation, you should contact the installer to see if they will come repair the roof for you. However, if you have had the roof for some time, and would like to repair it yourself, here are some tips to get you started.

Locate the Leak

Brown water spots on the ceiling are one of the most common indicators of a leak. But just because you see a brown spot, doesn’t mean that’s where the leak originated. Since water travels and leaks where it is easiest to drop, the leak could have originated almost anywhere on the roof. Your first plan of action is to determine where the leak is coming from.


Conducting a thorough inspection of your flat roof is one of the best ways to locate the source of the leak. Taking the time to inspect potential problem areas can also help you to prevent future leaks or problems before they start. Here are some things you should look for when examining your flat roof.

  • Examine the Drains – Check the drains to ensure that there is no debris blocking or clogging the drains. Clogged drains can prevent water from properly draining, causing it to pool on the rooftop and contributing to leaks.
  • Look for Patches – If your roof has recently been repaired, checking the patches is a great place to start. Inspect patches to be sure they are still holding tightly.
  • Inspect the Seams – If your roof has seams, check them to ensure that they are all tight and holding.
  • Check the Collars Around Pipes – The collars around pipes should have flanges to protect the openings in the roof.


The repairs process will depend widely on the type of flat roof you have.

  • EPDM Rubber Roofs

Repairs or patches to rubber roofs can be made with an EPDM rubber membrane patch. If the area has a blister, it is important you first drain it and dry everything completely before sealing it. You should also ensure that the supports beneath the roof are dry, and make sure there is no rot.

  • Tar and Gravel Roofs

Repairing a tar and gravel roof is relatively easy, once you find the leaking area. Since tar roofs are covered with gravel, it can be difficult to locate the source of the leak. To find the leak, walk the roof and look for area where gravel is missing. Exposed tar areas may have cracks or dried bubbles, which could be the source of the leak. Once you have located the area that is leaking, the repair process simply involves applying tar, mesh, and then gravel.

  • Modified Bitumen Roofs

Modified bitumen roof repairs that require torching are best left to the professionals. If the repair is a matter of a simple patch though, you could use an asphalt-based membrane to stop the leak.

Make sure that the membrane you use for repairs is compatible with the existing roof material. While modified bitumen roofing and tar and gravel roofs can use asphalt-based membranes, for EPDM or PVC roofs, it’s important to match the membrane with the current roofing material.

Finally, while it is possible to repair flat roofs, in some cases it may advisable to have the roof replaced. Of course, this depends upon the age of the roof, the type of roof, and its overall condition. Often, once older roofs develop a leak, it’s a sign that the roofing materials are starting to show their age and are becoming less effective at keeping water out. If you’re uncertain about the condition of your roof, contact a roofing professional to have them inspect your roof for you.

For more information on flat roof repairs in Toronto or the GTA, contact Essential Flat Roofing, Oakville Ontario’s flat roof professionals. At Essential Flat Roofing, we offer repairs and new roof installation, and would be happy to answer any questions you have.

Image: Groton School