Abstract
Low-slope roofing assemblies can be designed with a range of insulation and membrane-attachment methods. Various building and energy codes appear to assume fastening methods to have an insignificant effect on insulation value, meaning that design and effective values are essentially the same. Recent studies showing that mechanically fastened systems could have very significant loss of insulation value are reviewed. This study uses thermal losses shown in those recent studies and examines the practical effect on various roof assemblies. Fully mechanically attached systems are compared with those that use adhesive attachment for the membrane and part of the insulation assembly. The thermal losses are shown to be significant and are presented in terms of the economic loss of the insulation. The cost of lost R-value is contrasted with the cost of attachment. A system based on a first layer of mechanically attached insulation with a second layer of insulation and membrane being adhered is shown to be very similar in cost, once the lost R-value is included. Finally, the loss in energy efficiency is calculated over a 15-year time frame. When total system costs include fastening as well as energy efficiency, then mechanically attached systems are essentially equivalent to some fully adhered approaches. Overall, the work challenges the code assumption that fastening methods do not significantly impact insulation efficiency. Furthermore, the results have implications for any analysis that considers such factors as carbon footprint, since building-energy efficiencies might be lower than currently assumed.
Highlights
The journey towards more energy-efficient commercial buildings has generally involved reducing heat energy flow across or through various components of the building envelope
The introduction of thermoplastic roof membranes, starting with polyvinyl chloride (PVC) in the 1960s followed by thermoplastic polyolefin (TPO) in the 1990s, marked the beginning of an accelerating trend towards reflective roofing
An analysis by Burch, Shoback, and Cavanaugh found that metal fasteners reduced the overall thermal resistance of insulated metal deck assemblies from 3–8% depending on insulation thickness [6]
Summary
The journey towards more energy-efficient commercial buildings has generally involved reducing heat energy flow across or through various components of the building envelope. Architects and building designers have many specification options available that can assist in improving the energy efficiency of the building envelope, including thermal insulation, infrared-specific filter coatings on windows, and reflective roof membranes. An analysis by Burch, Shoback, and Cavanaugh found that metal fasteners reduced the overall thermal resistance of insulated metal deck assemblies from 3–8% depending on insulation thickness [6]. They used a finite difference model to analyze overall thermal resistance for assemblies using 50 fasteners per 100 square feet (5.38 per square meter)
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