BUILDING SCIENCE
Practical Application of Vacuum Insulation Panels
By Phalguni Mukhopadhyaya
In previous issues, NRC Construction has reported about the exciting potential of vacuum insulation panels (VIPs), which have insulating values of up to R-60 per inch.
The main hurdle to their use in buildings has been the possible loss of insulating value due to damage during construction. One step in overcoming this was the recent retrofitting of an institutional building in Whitehorse, Yukon. The pilot project demonstrated the feasibility of using VIPs on a wall exterior; ongoing monitoring has documented continued performance. Project partners included Yukon Housing Corporation, Yukon College, Panasonic Canada Inc. and the Energy Solutions Centre.
Retrofitting Walls
The wall selected for retrofitting was approximately 8.3 m (27 ft.) wide and 3.7 m (12 ft.) high. It was comprised of 38 x 140 mm (2x6) wood studs with fibreglass batt insulation and a concrete block exterior, with a nominal total insulation value of RSI 3.5 (R-20). The retrofit insulation goal was based on previous studies, which showed that the economic wall insulation level in northern locations to be in the order of RSI 8.8 to 10.5 (R-50 to 60). The retrofit increased the nominal R-value from 20 to about 50, with R-21 coming from the VIPs.
It was determined that the insulation level of the existing wall was adequate to prevent condensation problems. In addition, a continuous 0.15 mm (6 mil) polyethylene air vapour barrier was installed on the exterior of the existing block wall to further reduce chances for condensation within the retrofitted wall insulation. The amount of insulation added outside the new vapour barrier also conformed to the insulation ratio requirements of the 2010 National Building Code of Canada.
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Photo showing the 25 mm (1 in.) polystyrene (top and bottom), the VIPs (lower right), the 6 mm (1/4 in.) flexible foam layer (lower right), and the 25 mm (1 in.) polystyrene protective layer (upper left and centre). All the retrofitted insulation is shown at the upper right of the photo. |
Polystyrene board 25 mm (1 in.) was glued to the polyethylene to provide a smooth surface on which to mount the VIPs. Studs 50 x 75 mm (2x3 in.) were mounted on the polystyrene board and attached to the concrete wall with anchors. A jig was used to ensure accurate placement of the studs so that the VIPs would fit snugly between them. The VIPs, temporarily held in place with a peel-and-stick membrane, were mounted between the studs. The VIPs were covered with 6 mm (1/4 in.) foam material held in place temporarily with sheathing tape. This meant that no adhesive was in contact with the aluminum film cover of the VIPs, reducing the potential for mechanical rubbing on the VIP surface.
The cover layer of 25 mm (1 in.) polystyrene was sized to fit between the stud supports and was held in place by friction until the vertical steel siding was installed. Because the location of the support studs was accurate, it was possible to pre-drill a stack of steel siding and then to visually check during installation to make sure no siding fasteners were encroaching on the VIPs.
VIP Assemblies
The VIP assemblies were designed to minimize damage potential due to mechanical rubbing of the VIPs against adjacent materials from factors such as thermal expansion and contraction. Given the potential vulnerability of these vacuum insulation panels, the design allowed the VIPs to be easily replaced if a problem occurred. To do this, the steel siding, the 25 mm (1 in.) foam board and the flexible foam would be removed, the VIP replaced, and the coverings replaced.
The contractor found that the VIP installation proceeded well. Monitoring during the first winter indicated that the VIPs consistently accounted for about 70 per cent of the insulating value of the retrofitted insulations, meaning that there were no significant changes over time in the relative performance of the VIPs.
The successful installation and performance during the first Yukon winter provide optimism that Vacuum Insulation Panels will be suitable for both retrofitting and for new construction as improvements are made in manufacturing and installation methods.
Phalguni Mukhopadhyaya is a Research Officer with NRC Construction. He can be reached at phalguni.mukhopadhyaya@nrc-cnrc.gc.ca or 613-993-9600.
