BSC was retained to evaluate the ice damming issues at an administration building located in one of the parks in upstate New York. As part of this evaluation, the design and construction of the enclosure were reviewed along with the existing building conditions. In the review of the building it was determined that the ice damming occurs because of significant heat loss from the occupied and conditioned spaces coupled with a lack of attic/roof ventilation. To correct the problems, an effective air control layer should be provided, significant insulation (thermal control layer) added and attic/roof ventilation installed. The recommended strategy for improving ventilation in the attic space was to provide continuous soffit vents at the perimeter of the roof, and install gable and “button” vents. Due to aesthetic concerns and increased effectiveness, the approach maximized gable venting and minimizes “button” venting. To address the lack of an air control layer, BSC recommended installing closed cell spray polyurethane foam (2.0 pcf) against fiberboard sheathing to create both an air control layer and a thermal control layer. The rigid, vapor permeable fiberboard was to be installed in a manner as to provide a ventilation space underneath the roof sheathing and to create the manifold at ridge locations. A 2” layer of polyisocyanurate rigid sheet insulation with the seams taped was to be installed flush with the rafters to provide a continuous vapor control layer. This assembly is to be held in place with 1x4 wood furring and finished with gypsum board.
