Reroofing a Ballasted Roofing System

By Dymon BradyWe have recently completed a re-roof of a ballasted roof. This particular roof was an EPDM Ballasted System, meaning it was installed with EPDM and covered with rock layers. We replaced the EPDM with TPO membrane and replaced the roof, keeping the ballasted system for a minimal cost to the building owner.When installing a ballasted roof system, the membrane is loose-laid, meaning it is not traditionally fastened in place with membrane screws and plates. Instead, sheets of roofing membrane are laid over the roof and sealed only at the seams. It is successfully held in place by the weight of the rock ballast, typically about an inch and a half in diameter. These rocks are layered to create a weight of 10-25 lbs a square foot, securing the membrane below. This rock layer is additionally helpful in preventing the sun from beating down on the membrane below, as well as preventing punctures in the membrane, thereby lengthening the life of the roof.When reroofing a ballasted roof, it is not a good idea to leave the membrane intact but rather it should either be relief cut, or completely removed (as described in the next paragraph.) This is because the original or bottom membrane will shrink and pull away from penetrations such as skylights, pipes and joints. Also, if the new or top layer of membrane did happen to develop a leak, the water could run between the two membranes for hundreds of feet before it finds a way through the original membrane below. This makes it nearly impossible to locate and resolve leaks.Instead, we are faced with two options when reroofing a ballast system. First, we can make relief cuts in the original membrane in 10 X 10 ft grids. This way, if the membrane shrinks (which it inevitably will), it does not cause problems to the remaining roof. Also, if a mechanical repairman walks across the roof and causes a puncture penetration, we only have a small 10 ft radius to search for a leak source, as moisture will find their way through at the cuts.However, if we make these cuts to the membrane below, we might as well throw the membrane away. The remaining membrane does nothing to strengthen the roof. PVC membrane will actually curl at the edges and become brittle, something we refer to as ‘potato chipping’. This can make the new membrane layer bumpy and uneven, inhibiting the proper flow of water.Instead, Brady Roofing makes it a point to remove the original membrane and install new membrane over the top. This creates a clean, efficient new roof. By removing the original membrane, we eliminate the possibility of it bunching or causing uneven bumps on the roof.We do this using a technique called ‘wind rowing’. Instead of hauling all of the existing rock and gravel from the roof, which could cost thousands of dollars, we group the rocks into rows along the roof. We take about ten feet from each side and pile it in the middle to form a row. This exposed 10 ft increments of EPDM spaced 10 ft apart.We then removed the EPDM and put down a layer of TPO. In between these two rows of TPO, we still have an entirely built up rock level resting on an EPDM layer. We moved these rocks to lay on top of the TPO and exposed the EPDM. We removed this EPDM and lay down another strip of TPO. We had measured before we began the project, so we knew exactly where to lay down each row to make it perfectly straight and aligned as was necessary. All we needed to do at that point was to seal the TPO seams from the middle row to the outside rows, and lay the rock back on top of the new membrane.This simple process creates 30 ft of membrane, quickly and effectively installed, without needing fasteners in the seams. We were also able to keep the underlying rigid insulation, which significantly reduces the price of the project. Fasteners are still required through the new membrane around the perimeter, at angle changes, and around roof penetrations such as ventilation pipes and HVAC curbs etc. These fasteners are vital to keep the membrane from bridging or pulling away at the edges and corners as the roof system ages.The company we bid against was bidding much less, but they were not going to tear off the membrane or even relief cut it. They also were not going to do drip edge detail around the perimeter. We have found we are more thorough than many of our competitors. We take pride in being a better value because we do things the way they are supposed to be done. Brady Roofing is known for being a thorough, honest company with very experienced managers and installers. We are committed to providing the best quality roof possible. For a free roofing estimate, or if you may have any questions, contact us today and we will be glad to serve you.