5 Commercial Roofing Mistakes That Lead to Water Penetration

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Did you know that 98% of all roof repairs occur in penetrations or perimeters, meaning anything that protrudes through the roof or breaks the membrane? Some examples include curbs, drains, plumbing stacks, vent stacks, elevator shafts, antennae bases, electrical and copper lines, skylights, and penthouses. These areas present challenging repairs, and if they’re not done correctly could result in a leak. Here are some examples of what not to do on a roofing job.

  1. Don’t use non-compatible roofing materials (i.e., plastic cement on single-ply membranes).
  2. Don’t overspray with coating or you could have an insurance liability claim on your hands.
  3. Don’t cover electrical cords/conduits. These areas will need to be accessed at some point.
  4. Don’t clog drains. Keep them clear so they don’t lead to ponding on the roof.
  5. Don’t just poke a hole in the roof and put goop around it. Besides the fact that it doesn’t look very nice, it won’t be watertight.

There are many solutions for tough penetrations, but whichever one you choose, be sure to use a high-quality sealant to ensure correct waterproofing. Here are three methods a contractor can use to waterproof a challenging penetration:

  • For an MB or BUR roof system, seal using the three-coursing approach, which includes placing one layer of sealant, one layer of fabric, and one layer of sealant. The final step is to sugar-in matching granules with the SBS or BUR surface. The advantages of this approach are that it’s easy to use, no mixing is needed, and there is less waste, as the pouches are reusable.
  • For a metal roof or MB or BUR roof system, use TOPCOAT® FlexSeal™ Elastomeric Sealant. It is a similar approach to three coursing but uses a different sealant. It is compatible on metal, concrete, wood, SBS, APP, EPDM, and BUR substrates for gutters, detail areas, edge metal, and termination bars.
  • For a BUR or MB roof system, use an M-Curb™ Pitch Pocket System, which is made from solid urethane and designed to seal difficult penetrations on asphaltic roofs that can’t be flashed. This option requires no fabric or granules, as the material is pourable and bonds with the asphalt roof. Installation is fast and easy, and these curbs are very versatile, as they can be made in custom shapes to fit a variety of rooftop places.

All of the options above are approved for GAF warranties. Learn more about these flashing products in the links below:

MajorSeal™ Liquid Flashing

M-Curb™ Pitch Pocket System 

TOPCOAT® FlexSeal™ Elastomeric Sealant

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  1. Zach Thalman

    This is good to know. We were planning on building our own shed in the backyard because we have a lot of left over wood from building the house. I was planning on doing something really cheap for the roof, but I think I may spend some extra time making sure the roof is done well. The whole point of the shed is to keep my lawn equipment free from the rain and the elements.

  2. Vergese

    Thanks for these great suggestions for waterproofing sealant. I feel like the First is one of the easiest, and most important! Great to know that there you mentioned the best methods to avoid the water penetration. It is Important to be careful and pay attention on the quality of sealant if they’re not done correctly could result in a leak.

  3. Merle

    Yikes! This is a great article, and informative website overall. Just stumbling into GAF for the first time. You won’t believe how many times we’ve seen roofers perform #3 and #5 to cut corners! I will be sure to share this article with my fellow roofers!

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