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Published on Tue, 04/20/2021 - 09:42

Overview

We strongly recommend that whenever possible, contractors should avoid installing PowerGrip Universal Units (PGU) directly on a seam or field lap in the roof cover or membrane. This includes side laps, end-laps, flashing toe laps and any overlapping transitions of the roofing field sheet, patches or flashing materials.

If there is a field seam or overlap of roofing material in the exact location where a PGU unit is to be installed, we recommend moving the roof mount to another nearby location, where it can be installed on a flat, seam free, roof surface so it can more effectively perform its required function.

Image of PowerGrip Universal 11 installed

Issue and Background

There are instances where relocating the roof mount is not feasible and installation directly over a seam lap is ultimately required.

In general, the thickness of an overlapping seam varies based on the thickness of the roofing material.  Roofing materials range in thickness from about 0.045-inches on the low-end to over 0.20-inches on the high-end. Installing PowerGrips over the lap “step” may adversely affect unit’s ability to remain watertight since the anchor is being installed across a ‘step’ in the membrane where the surface is not uniformly flat.

PowerGrip units are designed to be watertight and have both a foam compression gasket, and a redundant sealant around the base. When they are installed over a ‘step’ or extra layer of roof cover, the foam gasket and sealant may not completely ‘fill’ the void or step created where the roof materials overlap. While this may not be an issue with thinner .045- or .060-inch thick roof covers, it is likely to be an issue with the thicker roofing materials such as bituminous cap sheets and modified membranes that can be up to 0.20-inches thick. 

Lastly, it is important to carefully check the workmanship of the overlapping roofing materials prior to installing a PowerGrip roof mount.  If the overlapping materials are not completely and fully sealed, glued, welded or otherwise adhered to each other in a waterproof manner, then installation over this ‘void’ will ultimately fail. 

Whenever a PowerGrip Unit falls directly onto a roof seam, follow the guidelines outlined below:

Solution

  1. Assess the seam. Do not attempt to install the PowerGrip Universal across any seam where the cover material that creates the ‘step’ is greater than .060-inches.
  2. Carefully check the seam quality.  Use a seam probe* to “rake” the seam with a slight amount of lateral pressure, looking for voids. The tool should not be able to lift or penetrate any gaps between the layers of the roofing material.  If any voids in the seams are identified, they need to be repaired and re-probed before proceeding with the PowerGrip installation.
  3. Remove any loose sealant outside of the overlap, and blow the seam clean, before installing the base plate.  Install a ‘cove’ seal of the roof manufacturer’s recommended water block sealant.  The cove seal should be forced into the “step” at the overlap, and long enough that it extends beyond the top plate of the PowerGrip upon completion of the installation.
  4. When installing the base plate, start all screws and compress the base gasket by about 50%.  Then tighten all screws through the overlapping roof layer first.  Tighten the screws on the top layer to fully compress the gasket, then tighten the remaining screws.  This process should effectively cantilever the base plate off the higher roofing layer. 
  5. Prior to installing the top plate of the PGU unit, apply a double application of sealant around the lower plate and the seams of the roofing materials. This may also be accomplished by applying the sealant normally around the top plate, and then applying an additional bead of sealant directly to the roof around the base plate. 
  6. Install and torque top plate normally, per the installation instructions.
  7. By following these steps carefully, you can minimize damage to the roof, and help to ensure a proper PowerGrip installation for long term performance.

* Typical roofing seam probes are cotter pin extractors, which are available from your commercial roofing distributor or a local auto parts store.

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