Thermal performance of insulated sheet steel assemblies

 ECONOMY AND ESTHETICS AT MONCTON HOSPITAL ATRIUM
For a 2007 atrium project at New Brunswick’s Moncton Hospital, steel cladding was a perfect fit. The material’s esthetic and economic capabilities meant it fulfilled the constraints and design goals of the $47-million project, which linked the new space to existing facilities such as ambulatory care and underground parking.

“With limited space for interfacing, steel was the material of choice because it is easier to manipulate in these conditions,” said Raven Spanier of Design Workshop, one of the project architects.

James Teichman of Maritime Canopies, the cladding installer, agreed.

“Steel is much easier to work with because everything is more true,” he said.

The material was used for 743 m2 (8000 sf) of steel cladding and standing-seam metal roofing, featuring linear panels, Z-bars, and galvanneal steel deck. Corrugated wall panels measuring 22.2 mm (7⁄8 in.), as well as 0.76-mm (1⁄3-in.) prepainted batten-clad roofing, were also employed.

In part, the material’s selection was due to its gloss retention and ability to colour match with the existing facility.

“Silver offers a richer look and matches other metal components,” said Spanier.

Thermal performance study
Insulated sheet steel assemblies provide lower heating and cooling costs for building owners across a variety of wall and roof applications in each of Canada’s climate zones. The Canadian Sheet Steel Building Institute (CSSBI) worked with the engineering and management consulting firm Morrison Hershfield to evaluate the thermal performance of several insulated sheet steel wall and roof assemblies. (More information is available at cssbi.ca/assets/resources/Design_Manuals/CSSBI-B20-15.pdf.)

Sheet steel wall assemblies employing notched Z-bars
A sheet steel wall assembly with notched Z-bars was used as the baseline wall application for the Morrison Hershfield evaluation. This assembly uses 152 mm (6 in.) of mineral wool insulation (R-4.2/inch) between a 24-gauge interior steel liner and exterior steel sheet cladding. Figures 1 and 2 include thermal performance evaluations for this application with different Z-bar spacing, insulation types, and thicknesses. Depending on insulation thickness and spacing of girts, these assemblies can reach insulation R-values of R-25 or R-48 to meet the needs of buildings in Climate Zones 5 through 8.

Sheet steel wall assemblies with thermal chairs
The same sheet steel wall from the previous section was also modelled with intermittent thermal chairs replacing the notched Z-bar from the baseline wall application. Assemblies employing thermal chairs traditionally reach R-values of R-25, making them appropriate for buildings in NECB Climate Zones 4 through 6. In Figure 3, thermal performance of this wall application with different horizontal spacing of thermal chairs is shown.

Insulated sheet steel roof supported by thermal chairs
The baseline roof assembly considered in the Morrison Hershfield evaluation included 22-gauge profiled cladding fastened to an 18-gauge hat section, supported by 254-mm (10-in.) thermal chairs with 273 mm (10 ¾ in.) of mineral wool insulation filling all voids between the cladding and liner. Figures 4, 5, and 6 show the thermal performance of this application with various thermal chair spacings, insulation levels, and thermal tape thicknesses. These variations of insulated sheet steel roof applications perform particularly well in terms of energy efficiency, meaning they are capable of meeting requirements for builders in Canada’s colder climate zones.

Insulated standing-seam roof
The insulated standing-seam roof is similar to the baseline roof, but features a different cladding shape and a different method of connecting the roof to the structure. Insulation in this application was draped R-19 batt, which was compressed between the hat section and the roof panel. Standing-seam roof applications can achieve R-values of up to R-56.7, and are suitable for building applications up to Climate Zone 7. Figure 7 shows the thermal performance of this application with a variety of insulation placements and types.

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