What is a Vacuum Insulated Panel?
Vacuum Insulated Panels, or VIPs, are a relatively new product making their way into buildings in the United States. Like other types of insulation, they can be used as stud cavity insulation or as continuous exterior insulation on structures.
As the name describes, VIPs consist of a panel with the air inside removed to form a vacuum. It isn’t a perfect vacuum, but the air pressure inside the VIP is considerably less than ambient pressure. The panels are airtight and do not absorb water vapor. They make good insulators because the vacuum almost completely eliminates conductive and convective heat transfer through the center of the panels.
VIPs have an R-value that can range from R-30 to R-60 per inch at the center of the panel and about R-20 for the whole panel (exact R-value depends on the manufacturing process and materials). The center of the panel will have a higher R-value than the edges, much like a window, as edges provide a thermal bridge for conductive heat transfer and lower the R-value of the entire panel. However, the whole-panel R-value is considerably higher than other insulations: fiberglass batts are around R-3.8 per inch, EPS is around R-4 per inch, and XPS is around R-5 per inch.
The trick to using VIPs is figuring out wall assemblies that can capitalize on their superior R-value while also protecting the vacuum, which is delicate compared to other building materials. VIPs can be installed on the sheathing plane of a building using adhesive. The material surrounding the VIPs in a wall is very important, because it helps protect the VIP from damage during installation. However, because the VIP is not continuous (for example, there will be joints between the panels) it brings the total wall R-value down. This is similar to what happens in a traditional stud-framed wall with fiberglass batts in the cavities – the wooden studs provide a path for heat to escape and reduce the total wall R-value. With VIPs, even if the “studs” were made of EPS insulation, the whole wall R-value will still drop more than the fiberglass wall drops with the addition of wooden studs. It is important to consider how to provide structure for VIPs while also minimizing thermal bridging.
As with any new building product, there are potential disadvantages of VIPs that must be considered. First, VIPs are manufactured in a factory and shipped to the building site, which means they can’t be cut or modified in the field. This means that detailed plans must be completed prior to construction and there is no flexibility in modifying them, unlike a traditional stick-framed wall.
VIPs also cost quite a bit more than other types of insulation. In addition to the more intensive manufacturing process, the panels have to be shipped to the building location. There are currently only a few manufacturers in the United States, so this could be quite a long distance.
Additionally, VIPs are very fragile and any punctures cause the entire panel to lose R-value dramatically, often bringing it down to around R-3 per inch, so building with them requires a great deal of care to avoid any potential sharp objects. More and more manufacturers are creating panels that have a VIP core but a more durable cover to protect it.
Finally, panels will naturally lose some vacuum over time. When they do, the R-value drops substantially. Manufacturers currently estimate the lifespan of the vacuum at 25 to 50 years. The seals must be treated carefully during the shipping and installation process to protect the vacuum insulation.
Overall, VIPs are an exciting technology that are poised to transform the building industry once we figure out the standards and techniques to incorporate them.