Top 10 No 7

Low-Slope Roofing Mistake No. 7: Missing T-Joint Patches

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One of the most notorious leak points on a roof is at the T-joint, where multiple layers of membrane come together. Sometimes installers neglect to patch them at all. And sometimes they’ve simply put the patch in the wrong place. 

In this segment of the Roofing it Right with Dave and Wally miniseries on the Top Ten Mistakes in Low Slope Roofing, GAF Senior Commercial Training Specialists Dave Scott and Wally Brown offer tips on welding a patch that fits to a “T.”

  • Make sure the patch is on the T-joint — the spot where all three layers meet — not just the top two. 
  • To make the T-Joint easier to weld (and harder for water to flow around), make a dog ear, or angled cut on the under layer.

Check out the episode here:

And be sure to check out the entire top ten list, along with the complete collection of entertaining and educational Roofing It Right episodes (muchos de ellos disponibles en español), at

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