Whole building demonstration of re-cover over an existing wet roof

摘要

Roof re-cover, the practice of installing a new roof over an existing failed roof, has become commonplace. The 1994 National Roofing Contractors Annual Roofing Survey reported that approximately 33% of current reroofing activity is re-cover. Market trends suggest that re-cover will become an increasingly more popular option. Moisture in the failed roof complicates the decision whether or not to re-cover and how to do the recover if that is the decision. If the root to be re-covered contains moisture that will not be removed during reroofing, this moisture must be able to escape from the roof system. Otherwise, moisture entrapped in the roofing system may eventually lead to the mechanical failure of fasteners and the roof deck, especially if it is metal. In 1991, the Oak Ridge National Laboratory (ORNL) surveyed its own roofing inventory and found that 164 buildings or 70% of the laboratory roof area needed reroofing. Because of the high cost of tear off and replacement, an alterative was sought. This paper describes the procedure employed to determine the suitability of a particular roof system on a laboratory building for re-covering. The procedure involves the use of field diagnostics, laboratory experiments and numerical simulations that demonstrate that the particular roof type can be re-covered. Furthermore, the building and roof system have been monitored for approximately 16 months after re-cover. The monitoring results are compared to the numerical simulations and demonstrate that the roof system is drying and that the reroofing strategy that they used is cost-effective.