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To Prove a Point, Melt Some Ice

A second ‘Ice Box Challenge’ aims to show the advantages of building to the Passive House standard

Ice melts slowly. A visitor to Seattle's Occidental Park peers into a small Passive-House-compliant structure where a ton of ice is melting. It's part of a demonstration aimed at showing differences between code-compliant and Passive House buildings.
Image Credit: NK Architects

Passive House advocates in the Pacific Northwest have organized an unusual public demonstration aimed at proving just how much energy can be saved with superinsulation and airtight design, a contest not unlike a county fair come-on where visitors are asked to guess how many pebbles will fit into a one-gallon jar.

Only in this case it’s how much of an original ton of ice will be left after sitting inside an unrefrigerated building in the middle of summer for several weeks.

Earlier this year, Passive House Canada (with the backing of a number of other sponsors) built two small structures and placed them on a sidewalk in Vancouver, British Columbia. One was constructed to meet the Passive House building standard, the second to the provincial building code.

Just under a metric ton (1,000 kilograms) of ice was placed in each one, and after 18 days the enclosures were removed to expose what was left. According to Canadian Consulting Engineer, the remaining ice in the Passive House structure weighed 639 kilograms, compared to the 407 kg of ice in the BC code-compliant enclosure, when the event ended on August 14. Prizes offered to the people whose guesses were the closest included tours of Passive House buildings in the Whistler and Vancouver areas.

The backdrop is a new zoning law that will eventually require all new houses in the city be built to the Passive House standard, Business Vancouver reported.

A second round in Seattle

Earlier this month, The Ice Box Challenge moved 142 miles south and set up shop at Occidental Park in Seattle, where a similar “ice reveal” was planned for today (September 28).

This time, the contest pits the Passive House standard against Seattle’s building code. During the 20-day melt-down, visitors could take a peek through windows in the sides of the small buildings to see how the 1,200-pound blocks of ice were faring.

Brittany Porter, a project architect at NK Architects, one of the primary sponsors of the event, said that the idea for bringing the demonstration to Seattle was hatched at a Passive House conference in the spring attended by a number of people from the Canadian Passive House group. Similar demonstrations have taken place in Europe, where Passive House construction is more common, and the face-off seemed like a good way of introducing more people in the Northwest to Passive House features.

The houses are basically the same, with a few notable exceptions. The code-compliant building has 2×6 framing and is insulated with Roxul mineral wool cavity insulation to R-21. It has double-pane windows. The Passive House version has 2×12 framing plus cavity insulation and a continuous exterior layer of Roxul insulation for a total R-38 envelope. It gets triple-pane windows, higher quality air-sealing tapes, and a more careful window installation.

Blocks of ice with an aggregate weight of about 1,200 pounds have been melting inside specially designed demonstration enclosures in Seattle, a repeat of the Ice Box Challenge that took place earlier in the year in Vancouver, British Columbia.

Porter says that the buildings were run through standard energy modeling to make sure they would comply with their respective standards (but there were no blower door tests).

NK Architects and Passive House Northwest weren’t offering any prizes for the best guess on the ice melt, but Porter said that public interest has been high nonetheless.

“Luckily it’s in Occidental Park where there are food trucks and a live music in the summer,” she said by phone. “It’s sort of the happening spot for lunch time. There are always people checking it out and asking questions. The biggest question is always, ‘What’s the difference between the two boxes?’ Everyone is always pretty impressed: There is more insulation, better construction quality with the taping and the air sealing and another pane of glass. That’s really all there is.”

Good timing

Sponsors managed to squeeze in the project between the Seattle Design Festival opening on September 9 and this weekend’s North American Passive House Network Conference (which promotes the German-based Passivhaus standard rather than a similar standard published by the Passive House Institute U.S.) Results of what Porter calls a “public science demonstration” will be revealed just as the conference gets up to speed.

“It’s just a nice visual way for the public to see some of the ways in which designing a better building can save up to 75% in energy use — and I expect that will be the difference in ice melt — about 75% more ice melt in the code-built building,” she said.

Seattle’s Ice Box Challenge follows by a year a demonstration staged by Olson Kundig Architects on the same spot: the melting of a 10-ton block of ice to mimic how the Earth’s ice caps are melting.

“I’m hoping this is sort of a hopeful, optimistic type of installation,” she said. “Last year was meant to be a shock-and-awe thing, but done very beautifully. We’re in the same location, in the same amount of time, and we’re coming in with this piece that’s just proposing a solution, and a really achievable solution. That’s why we’re really excited.”

Next year the exhibit travels to the Oregon Museum of Science and Industry in Portland.


  1. GBA Editor
    Martin Holladay | | #1

    Response to Charlie Sullivan
    You get my "favorite comment of the week" award. Thanks.

    Architects aren't mathematicians. The majority of Americans don't understand percentages, and in this country, architects are mostly American.

    In the article you refer to ("Does a Passive House Use 90 Percent Less Energy?"), I estimated that the typical Passive House uses less energy than a code-minimum home -- somewhere between 24% less and 54% less. Data from two people -- David Murakami Wood and Katrin Klingenberg -- became available after my article was written. David's data fell smack in the middle of my range.

    Katrin's data indicate that savings may be less than I estimated -- on the order of 17% to 28%.

    In other words, nowhere near 90% savings.

  2. vensonata | | #2

    The Vancouver experiment is more understandable as: the code house lost 793 lbs. and the passivhaus lost 561 lbs. Or the code house paid $793 in heat bills and the passivhaus $561. The passivhaus saved $232. The passivhaus saves 30% on heating bills. Now that is actually a tribute to Vancouver code building rather that a diminishment of passivhaus standards.

  3. STEPHEN SHEEHY | | #3

    Without a cost comparison, I'm not sure this proves much, other than that better insulation and air sealing, with better windows, is more energy efficient. Duh!
    Why R 38? R 10,000 would be even better, especially with sextuple pane windows.
    They could have used the same building envelope and called it a pretty good house.

  4. GBA Editor
    Martin Holladay | | #4

    Response to Stephen Sheehy
    You're right. If a version of the Passivhaus Standard (one requiring R-38 walls) ever becomes code, it would be possible to build two new huts: A Passivhaus hut with R-38 walls and an even better hut with R-76 walls. Clearly, the Passivhaus hut would lose this contest -- and the contest would prove nothing.

  5. charlie_sullivan | | #5

    Math education for architects
    "Save up to 75%" would mean going from a baseline code-built building down by 75% of that baseline, to 25% of it, a factor of 4 difference in energy use. That's not consistent with the other statement here about 75%, described as as an increase from the passive house by 75%, or a factor of 1.75. Those two statements sound the same to the mathematically illiterate, but their meaning differs by more than a factor of two. The former is not plausible given the description of the boxes or the experimental results, in which the code-build house melted 57% more ice, and the passive-house box melted 36% less ice.

    It is easy to let sloppy statements slip in a spoken interview. But a similar statement appears on the NK Architects blog.

    On the ice box challenge web site, it's framed as the idea that passive house buildings "use up to 90% less energy for heating and cooling than other buildings do." That reminds me of the recent discussion here about that 90% less energy claim. Maybe it's not that the people who say that really think that they can reduce energy use by a factor of 10. Maybe it's just that they don't understand how percentages work.

    [Edit: it's also easy to let sloppy typos slip in an online comment. I hope I've gotten them fixed now.]

  6. Reid Baldwin | | #6

    Cooling load v heating load
    Since we are comparing cooling loads instead of heating loads, why do they focus on the wall insulation. Both buildings appear to have white roofs and to be located in the shade. A more meaningful demonstration would have the same color roof that is common in the region and be out in the sun. How does the roof insulation compare? The window fraction looks pretty low compared to typical buildings. The number of panes in the windows is not as important as the SHGC. With air leakage being such an important aspect of passive haus, why no blower door testing?

  7. Bronwyn Barry | | #7

    Oakland Ice Box Challenge - More Results
    Scott - thanks for writing about these fun demonstrations! Another version was recently held in Oakland and ran concurrently to the NAPHN17 conference, just two blocks away. Attendees were encouraged to visit the two boxes and take part in the online competition to guess the weight of the remaining ice at the end of the week.

    The California team designed and built their boxes to be more representative of typical California homes. They installed two windows in each box - one facing south and the other facing west. Triple-pane and double-pane units were installed in the PH and code boxes respectively. This provided a great opportunity to not only test the influence of solar heat gain in a sunny climate, but also see just how well the 2016 Cal Residential Code stacked up to Passive House standard for this region, which meant only a little more insulation and better windows. (Our team was worried the results would not be too different.)

    Outside temperatures for the week of the experiment ranged in the low 70's, with full sun all day. The boxes were opened and the runoff from the ice was removed via the single-hung windows each evening. By the end of the week, the Passive House box retained DOUBLE the amount of ice compared to the code-compliant box. Exact results may be viewed here:

    We could draw a number of conclusions from all three of these Ice Box Challenge experiences. I've followed them all closely and think that they'd make an excellent basis for an undergraduate thesis study. What I've found most notable are the non-performance-based results evident in the remaining ice from all three locations: in Vancouver, the code-box ice was noticeably dirty - a result of the fires in the surrounding region - but the Passive House box ice remained clean and clear. This demonstrates an added benefit of more rigorous air sealing. In Seattle, the ice both shifted inside the box and melted much more unevenly than that of the PH box. In Oakland, there was barely enough ice left in the code box to draw additional conclusions, other than the code compliant structure clearly overheated more than its Passive House equivalent.

    You'll likely be able to see similar boxes in your own town soon. As you reported, the Vancouver boxes will be traveling on to Portland, OR. The Oakland boxes will head down the coast here early next year. Based on recent email exchanges, I understand that New York and Pittsburg may also be hosting their own Ice Box Challenges, all using local code vs localized Passive House assemblies. New Zealand also hosted their own Ice Box Challenge recently in Christchurch, so it looks like we’ll learn a lot more about how ice melts in various climates across the country and around the world. Who knew that would be so much fun?!

  8. Expert Member

    Vancouver Standards
    There is a misapprehension in the article that Vancouver will eventually require all buildings to be built to Passive House standards. What the municipal council has adopted is the Step Code, an incremental increase in energy efficiency eventually leading to standards close to those advocated by Passive House. There is no relationship between the new code provisions and Passive House standards or certification beyond that they both lead to energy efficient design.

    How this will play out in practice will be very interesting. The most common form of housing now being built in Vancouver are curtain-wall high-rise condominiums, which don't usually meet current code energy requirements. Making that housing form meet very stringent new levels of efficiency will be extremely challenging.

  9. Bronwyn Barry | | #9

    Training available
    Malcolm - I'd encourage you to take one of the many Passive House training courses now widely available all across North America: You'll be relieved to learn that building high-rises, even using curtain-wall assemblies, is not as hard as you appear to believe... It's currently being done in much more challenging climates than Vancouver, where Passive House certification is now being offered as an alternate pathway for code compliance, in lieu of the step code. The CoV is offering a number of substantial relaxations in their zoning code for those opting to use the certified Passive House pathway. Here's their website with further details:

  10. Expert Member
    MALCOLM TAYLOR | | #10

    You have missed my point about the typical construction the development community currently builds in Vancouver. I probably worded it poorly. The construction industry, the largest generator of taxes and driver of Vancouver's economy (and arguably a constituency that few municipal politicians can survive without the backing of) has been used to producing high-end housing with poor envelopes. Getting them onside is what is going to be challenging.

    You probably don't remember, but some time ago we had a discussion where I expressed my concern with the Passive House agenda of forcing people to adopt the standard by getting it adopted in municipalities or included as part of building codes - something you denied.

    And now here we are with Passive House attempting to do just that in Vancouver. The consolation you are offering, rather condescendingly considering you know nothing about my professional skills, is to take the Passive House training. Forgive me if I decline.

  11. Bronwyn Barry | | #11

    Calm down to frantic, Malcolm!
    Malcolm, forgive my impertinence in suggesting you may benefit from some additional education... Rather than taking my word for it, I was hoping you'd be able to figure out yourself that "making that housing form meet very stringent new levels of efficiency will be extremely challenging" is not that challenging after all... Here’s an assembly high-rise architects will be familiar with in Vancouver, using a section profile just one pane different from those currently being specified: (It’s being offered through Unison Windows in North Van: The Schüco curtain wall assembly used on the Bullitt Center in Seattle is now widely available across North America, with an easy option to select ‘to passive house standard’ here: If that’s too limited a choice for you, here's a link to 38 alternate options, all certified by PHI for the cold-temperate climate of Vancouver: Vancouver developers will have no trouble using these assemblies if it means their projects are fast-tracked or they receive other incentives.

    I'd also like to address your "concern with the Passive House agenda of forcing people to adopt the standard by getting it adopted in municipalities..." (I remember our discussion.) Please rest assured that many smart municipalities, including those of New York City and the City of Vancouver, are impressively capable of recognizing the benefits of the Passive House standard all on their own. (No strong-arming required.) As far as I know, the Passive House standard is still voluntary in both those cities. Our community’s collaboration with the United Nations ( on their building framework is also all based on member nation’s voluntary signing of the Paris Agreement. I promise not to strong-arm your city into meeting the Passive House standard. Despite your obvious disdain, I can also promise that the training will still be open to you and anyone else who’d like to learn how to design what will soon become the new code minimum performance targets, whether it's called 'Passive House' or not:

  12. Expert Member
    MALCOLM TAYLOR | | #12

    Would you suggest that course to Martin? John Straub, Joe Lstibek? Bill Rose? Do you know more than them? Better than them?

    The Passive House designers and builders I've had contact with seems well intentioned, but the closer you get to the centre of the organization, or its propaganda arm, the more ideological it appears. Despite your constant denials, Passive House itself makes quite clear it wants to get their standard accepted to the exclusion of others. The vehemence of your fratricidal battles with American Passive House also show you don't want a plurality of approaches.

    There are a lot of well-educated practitioners who are interested in the same aims you profess, but believe they can best be achieved by other means. You have consistently shown no genuine interest in exploring an open examination of any topic here beyond a blanket defence of Passive House. Would it be fair to say your new message to me is that once Passive House has out-manoeuvred alternate approaches, you promise the door will still be open for me?

  13. Bronwyn Barry | | #13

    Hmmm... perhaps the ice needs to be 'broken' and not melted?
    Malcolm - let's just bury the hatchet, shall we? I hope you'll be hanging out with Joe Lstiburek's in his basement, smoking cigars, if and when "Passive House has out-maneuvered alternate approaches."

    In the meantime, I look forward to seeing other ice-melting demonstrations happening all across the country, using the building assemblies of your own personal favorite path to lower carbon emissions.

  14. Expert Member
    MALCOLM TAYLOR | | #14

    That's more than fair. Cheers.

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