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Ice Box Challenge

Two weeks ago, on August 14th, the results were finally revealed – Passive House box: 639 kg, BC Building Code: 407 kg.
In a period of 18 days, the ice block in the PH box had melted off 361 kg, while the ice block in the BCBC box lost 593 kg. That’s a difference of 232 kg, meaning almost 65% more ice melted in the BCBC box than in the PH box.
That’s pretty impressive – or is it? Some people have questioned whether the result was really all that remarkable. After all, Passive House construction is claimed to be up to 90% more efficient.

Such criticism is fair, but one should take into consideration that the structures were small and temporary. Both affect performance.

These days, windows keep getting larger and larger. The elevation these windows are on is rarely taken into consideration – except when building a Passive House. Large windows on the North or East elevation result in larger heat losses, which is why in PH construction, fewer windows are used on these elevations, and their size is relatively small. However, on the BCBC box, the window used was also a small window, hardly the size of an average window these days. With windows still being the weakest part of the building envelope, this gave the BCBC box an advantage over a typical house built to the code.

The window choice, too, gave the BCBC box an advantage. Rather than choosing a low end sliding window with an inferior seal, a high end EuroLine 1400-series casement window was used. This window not only has a tighter seal than the average window being used these days, but at 1.53 W/(m^2*K) the u-factor of the window used also far surpasses the u-factor required by the BCBC (1.8 (W/m^2*K)).

On the other hand, the PH box was at a disadvantage, as in a temporary structure it is much more difficult to achieve the same kind of seal and insulation as in a permanent structure. Of course insulation plays an integral role in the PH standard. Much attention and care is paid to not create any thermal bridges, and a smoke test is perform to find and seal even the smallest air leaks.

Finally, building codes all across the world are improving, with many cities, and entire countries, aiming to adopt the Passive House building standard as their national building code standard. While a Passive House can still be 90% more efficient than an older building, the difference will be less, compared to a new home being built to current standards. And that’s a good thing.

We still think that the results achieved in the Ice Box Challenge were pretty impressive – but we look forward to the day when both structures will perform exactly the same.