The Icebox Challenge Comes to Glasgow

When Shaun St-Amour and Chris Hill did the first Icebox Challenge in Vancouver in 2017, I thought it was a silly idea. I mean, watching ice melt is perhaps only slightly less boring than watching paint dry. The "challenge" part of it was to compare a shed-sized icebox built to local building code standards (for buildings, not iceboxes) and another constructed with insulation, window, and air sealing to Passivhaus standards. You stick a metric ton of ice in each and watch them melt. Really, that's it.

But wait, there's more: It is also a contest where the person who guesses the weight of the ice remaining wins a prize. And it turned out to be a really effective way to show how effective the Passivhaus standard is at reducing heat loss or, in this case, heat gain. Many people think Passivhaus design is for cold climates, but as the Icebox Challenge proves, it can keep the heat out as effectively as it keeps it in.

Watching ice melt was hot, and the Vancouver iceboxes were shipped to Seattle and then to New York City. The sport became so popular it has been repeated around the world, including in Glasgow in the runup to the United Nations' delayed COP26 climate summit this fall.

An interesting twist in the Glasgow challenge is it was also a design competition among Scottish schools, which was won by students from Robert Gordon University in Aberdeen. They say of the design concept: "reinterpreting the highland vernacular, the design creates a balance a natural but vibrant aesthetic."

The box is made from a series of portal frames that can be carried by four people and assembled easily. They are basically trusses filled with wood fiber; this would be a strong and efficient structural system for a full-sized building.

Perhaps I am turning into Passivhaus architect Elrond Burrell who looks at buildings and channels Hayley Joel Osment, saying "I see thermal bridges," those places where structural elements allow localized heat transfer, such as where the roof meets the wall. I certainly see them here.

The Glasgow challenge started in the middle of a heatwave on July 23. Each icebox was loaded up with a cubic meter of ice weighing 917 kilograms. I thought this was weird; that's 2021 pounds—are they buying a ton of Imperial/American ice? Isn't the definition of the metric system that a metric ton of ice should also be a cubic meter? In fact, no, a cubic meter of water weighs a metric ton, but water expands when it freezes, so a cubic meter of ice weighs less. Another lesson learned from the icebox challenge.

After 11 days, the ice in the box built to Scottish codes was gone; the Passivhaus box still had 266 pounds (121 kilograms) of ice, at least before the dog ate their homework. Andrew Workman, who had the closest guess, said: “I picked 120 kg for the efficient Passive House as I thought there would be about 10 percent remaining, and I added a little for buffer. I am really surprised that I won, especially considering the Glasgow heatwave." He is off to a Passivhaus B&B as his prize.

The great thing about the Icebox Challenge is it's usually really hard to explain the benefits of Passivhaus design. It's not like solar panels that people can point to: it's all in the windows, walls, and the build quality. But as they note on the Icebox Challenge website:

"The result of the Glasgow Ice Box Challenge vividly demonstrates the advantages of better buildings. While the two boxes looked the same from the outside, save for the red and green herringbone pattern, internally the window glazing, insulation levels and attention to detail to reduce thermal bridges made all the difference. These three out of five indispensable principles for Passive House buildings contribute to keeping the heat out in summer. Especially this summer, when Glasgow experienced a heat wave, the results demonstrate how the Passive House Standard provides cooler and more comfortable indoor temperatures and future-proofs buildings against increasing global temperatures."

The Icebox Challenge is taking a little tour and then returning to Glasgow for COP26. After reading Treehugger writer Sami Grover's post about how the United Kingdom is turning to predatory delay as a tactic, perhaps it should take this show to London and park it on Downing Street. In the fight against the climate crisis, every building should be a Passivhaus building.