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Title
Thermal Performance Evaluation of Innovative Metal Building Roof Assemblies
Thermal Performance Evaluation of Innovative Metal Building Roof Assemblies
Date
9/2011
9/2011
Author(s)
Daniel Walker; Abdi Zaltash; Jerry Atchley
Daniel Walker; Abdi Zaltash; Jerry Atchley
Page(s)
Keyword(s)
ASHRAE; building envelope; energy efficiency; hot box; IECC; MBMA; U-factor; R-value
ASHRAE; building envelope; energy efficiency; hot box; IECC; MBMA; U-factor; R-value
Abstract
The Metal Building Manufacturers Association (MBMA) and Oak Ridge National Laboratory (ORNL) began collaborating during the summer of 2009 to develop and document the thermal performance of new and innovative insulated metal building roof assemblies. The impetus for this work was the ongoing effort to increase the energy efficiency of building envelope assemblies used in nonresidential (conditioned) and semi-heated applications. Because metal buildings are used in approximately 40 percent (by square footage [1]) of all low-rise nonresidential construction, this is an important construction type for any overall effort to achieve better energy performance. The model energy-conservation codes such as ASHRAE Standard 90.1 and the International Energy Conservation Code (IECC) set minimum requirements for building insulation based on previously tested assemblies and economic analyses to determine whether sufficient cost savings can be achieved that offset the first cost of added insulation. Because ASHRAE 90.1 and IECC are undergoing significant increases in required efficiency, additional high-performance roof assembly details are needed beyond those that originally were used to set the minimum requirements. Innovations in construction techniques and insulation materials also have taken place in recent years that are not accounted for in the previously tested designs. Therefore, a new set of highperformance roof assemblies is needed to continue making progress toward lower energy use in buildings. The ongoing work conducted by MBMA and ORNL thus far includes hot box tests of four innovative metal roof assembly modules. The goals for this work were to produce constructible metal roof assemblies that will achieve an overall U-factor between U-0.02 and U-0.04 Btu/h·ft²·°F and have the potential to be economically viable. The assemblies considered were developed taking into consideration thermal bridging through metal components, isolating the steel roof framing members (z-purlins) and maximizing the effectiveness of various insulation materials. In addition to the thermal performance, consideration also was given to constructibility, durability and structural integrity.
The Metal Building Manufacturers Association (MBMA) and Oak Ridge National Laboratory (ORNL) began collaborating during the summer of 2009 to develop and document the thermal performance of new and innovative insulated metal building roof assemblies. The impetus for this work was the ongoing effort to increase the energy efficiency of building envelope assemblies used in nonresidential (conditioned) and semi-heated applications. Because metal buildings are used in approximately 40 percent (by square footage [1]) of all low-rise nonresidential construction, this is an important construction type for any overall effort to achieve better energy performance. The model energy-conservation codes such as ASHRAE Standard 90.1 and the International Energy Conservation Code (IECC) set minimum requirements for building insulation based on previously tested assemblies and economic analyses to determine whether sufficient cost savings can be achieved that offset the first cost of added insulation. Because ASHRAE 90.1 and IECC are undergoing significant increases in required efficiency, additional high-performance roof assembly details are needed beyond those that originally were used to set the minimum requirements. Innovations in construction techniques and insulation materials also have taken place in recent years that are not accounted for in the previously tested designs. Therefore, a new set of highperformance roof assemblies is needed to continue making progress toward lower energy use in buildings. The ongoing work conducted by MBMA and ORNL thus far includes hot box tests of four innovative metal roof assembly modules. The goals for this work were to produce constructible metal roof assemblies that will achieve an overall U-factor between U-0.02 and U-0.04 Btu/h·ft²·°F and have the potential to be economically viable. The assemblies considered were developed taking into consideration thermal bridging through metal components, isolating the steel roof framing members (z-purlins) and maximizing the effectiveness of various insulation materials. In addition to the thermal performance, consideration also was given to constructibility, durability and structural integrity.