Waste Issues to Consider When Tearing off a Rooftest

By Thomas A. Westerkamp

November 2014

Managers face a major challenge in deciding whether to tear off an existing roof to install new insulation and membrane or to overlay a new membrane and insulation over the existing roof. Either choice can be risky business.

In the typical tear-off, the roofer removes everything down to the wood, metal or other deck materials, including ballast, membrane, vapor barrier, and flashing, leaving the contents under the roof vulnerable to bad weather. After repairing any deck damage, the roofer installs a new vapor barrier, insulation, flashing, and membrane.

Of particular concern with such projects are flashings and connections to roof drains, scuppers, and downspouts, which also must be replaced to accommodate new roofing materials. Since all the old material comes off, this method generates the most waste and is more costly than an overlay.

In an overlay, the old roof becomes the base. The roofer scrapes off the ballast, if there is ballast to contend with, and installs the new vapor barrier, insulation, and membrane over the existing roofing. Leaving some of the material on means less waste to dispose of, but it still leaves the roof vulnerable at flashing and penetrations.

This method can be complicated because using existing, damaged materials as a base can result in persistent leaks between the old and new materials. Leaks might not show up right away, but if they do, they are difficult to troubleshoot because the source can be far from where the leak appears.

Where and when is recoating a roof the most appropriate solution? Recoating can be effective with any compatible roofing materials, including over decks of concrete, blistered foam, metal, rubber EPDM, TPO and wood. The key to success with recoating is the integrity of the deck. If it is structurally sound, even if leaks have started and some areas need deck repairs, managers can gain several more years of service from the existing roof at the lowest cost. The process produces little or no waste, and it results in better ultraviolet and thermal protection, as well as seamless leak repair.