Founded in 1910, Rosco Laboratories is a multi-national producer of equipment, software and products for the theatrical, film, and television industries and architectural environment. As with every aging flat roofing system, water leakage was becoming a recurring problem at Rosco’s Stamford, Conn., facility. The severity of the leakage was further exacerbated by the lack of roof drainage (only two roof drains serviced the entire building) and poor deck slope conditions (less than 1/16 inch per foot).
Rosco representatives employed traditional methods to control and/or collect the moisture within the building by use of several water diverters. This technique was effective but Rosco representatives soon recognized this was not a viable long term solution as the physical integrity of the roof structure (deck) became a principal concern to the safety of the building occupants.
The Fisher Group LLC, an Oxford, Conn.-based building envelope consulting firm was retained by Rosco in March 2009 to survey the existing site conditions and determine the need for roofing replacement. The existing roofing construction, which consisted of a conventional two-ply, smooth-surfaced BUR with aluminized coating, exhibited numerous deficiencies (most notably severe alligatoring) and was deemed unserviceable. Construction documents, including drawings and specifications and a project phasing plan were developed by Fisher Group to address the planned roof replacement.
Bid proposals were solicited from prequalified contractors in June 2010, and F.J. Dahill Co. Inc., New Haven, Conn., was awarded the contract on the basis of lowest bid.
The building basically consists of a 1-story steel-framed structure constructed in the 1970s. It is a simple “box”-style configuration, which is conducive to manufacturing.
In conjunction with design services, destructive test cuts were made by Fisher Group in several roof sections as necessary to verify the existing roofing composition, insulation substrate, moisture entrapment, and substrate/deck construction. A total of four distinct “layers” of roofing were encountered at each test cut. The existing roofing construction consisted of alternating layers of smooth- and gravel-surfaced, multi-ply felt and bitumen built-up roofing. The bitumen contained throughout the construction was fortunately asphalt-based. Succeeding layers of roofing were spot mopped or fully mopped to the preceding layer (system). The combined weight of the roofing construction was estimated to be upwards of 20 to 22 pounds per square foot when considering the moisture content. This is excessive weight.
It is interesting to note that a minimal amount of roof insulation was present in the existing construction. Insulation was limited to a single layer of 1/2-inch-thick fiberboard. Additional insulation would need to be provided as part of the replacement roofing construction to increase the roof’s thermal performance and comply with the prescriptive requirements of the Connecticut State Energy Conservation Construction Code.
The structural substrate, or decking, is conventional in nature, comprised of poured gypsum roof decking. The roof decking incorporates 1/2-inch gypsum formboard loose laid between steel bulb-tee supports spaced about 32 inches on-center. The poured gypsum roof decking in this instance was utilized as the structural substrate and for insulating purposes. Poured gypsum roof decking has a minimal insulating value of perhaps R-2 to R-3, which is obviously considered to be minimal by present standards.
A representative number of bulk material samples were obtained by Fisher Group from the existing roofing construction as necessary to determine the material composition. The sampling included field membrane roofing plies, coatings and cements, and associated roof penetration and perimeter flashings. Laboratory analysis revealed that the second, third and, in some instances, fourth roofing “layers” (field membrane plies) contained varying amounts—5 to 10 percent—of asbestos (chrysotile) which would necessitate full abatement of the roofing construction.
PHOTOS: The Fisher Group LLC