News Treehugger Voices Passivhaus Challenge Shows How Well Passive House Buildings Hold the Heat It may be cool outside but inside, it's warm and toasty. By Lloyd Alter Lloyd Alter Facebook Twitter Design Editor University of Toronto Lloyd Alter is Design Editor for Treehugger and teaches Sustainable Design at Ryerson University in Toronto. Learn about our editorial process Updated February 22, 2021 02:06PM EST Fact checked by Haley Mast Fact checked by Haley Mast LinkedIn Harvard University Extension School Haley Mast is a freelance writer, fact-checker, and small organic farmer in the Columbia River Gorge. She enjoys gardening, reporting on environmental topics, and spending her time outside snowboarding or foraging. Topics of expertise and interest include agriculture, conservation, ecology, and climate science. Learn about our fact checking process Share Twitter Pinterest Email Shepherd's Barn EnerPHit . Mark Siddall News Environment Business & Policy Science Animals Home & Design Current Events Treehugger Voices News Archive According to architect Mark Siddall, the Passivhaus Challenge – to see how long people who live in Passivhaus (also known as Passive House) or EnerPhit (the standard for renovations) could go without turning on their heat – was a spur of the moment idea. He tells Treehugger: "...the idea came after seeing how Shepherd's Barn EnerPHit [shown in photo above] had coped with some of the colder weather recently. I got to wondering how long a Passivhaus could go without heating. Could it coast through a week? On a Saturday night, I sent a cheeky text to [clients] Paul and Sonny. Would they be willing to switch the heating off for a week, or until it got "too cold"? I was thrilled when Paul gave me the thumbs up. Somewhat emboldened my curiosity was peaked, would other clients take part? ... I messaged Mick Woolley from Larch Corner, [seen on Treehugger here] would he be game? Much to my surprise, he said yes as well." He then decided to put it up on Twitter. "As I saw it this little experiment was taking place anyway, I had no expectations that other people would actually join in." Siddall set up the format, asking for the temperature in Celsius and also a request: "feel free to add a little about how you feel that would give a little insight into your personal experience." Then day by day, interest grew, it became a phenomenon; people with certified Passive House buildings, and near Passive House, all over the world. Mark asked for the temperatures in Celsius but the Treehugger standard is to use Fahrenheit, so I whipped up a conversion table: Celsius to Farenheit conversions. Lloyd Alter The challenge is only halfway through, but I am showing a few of the most recent entries, except for this one from George Mikurcik's Old Holloway Passive House; it's my favorite these days, and once again he's got the dog in the photo. You can see the dog inside the house here. We asked last winter how the house was holding up and were told that the careful placement of windows made a difference; there was no Passivhaus Challenge last year but they still rarely used the heat. "It’s all very well that the house is comfy in summer but what about when it gets cold out there? How are we going to cope with no radiators? Well, we needn’t have worried. As the season was turning colder, we were getting more and more ‘free’ solar gain from the lower sun, effectively balancing out slightly increased heat losses through the building fabric. It wasn’t until one evening in November when we lit the small wood stove for the first time. On average, we now light the stove for an hour or so every other evening, sometimes less often. As long as the sun is shining, the house maintains the temperature beautifully." Here's the latest from Old Holloway; cooking a roast seems to help. The only house in this challenge that I have actually visited is Ben Adam-Smith's (seen on Treehugger here) and I am pleased to see that it is holding up to the challenge. The Shepherd's Barn renovation is also holding up. Renovations have a slightly more relaxed standard for air infiltration and energy consumption, so one might expect it to not do as well, but it is still, after two and a half days, a sort of comfy (by English standards) 64 F, but I bet that the heat comes on soon. Andrew Michler's (seen on Treehugger here) house is in Colorado, and it is cold there in either Fahrenheit or Celsius. Alas, the water line from his cistern is not built to Passiv House standards and froze up. John Semelhack is in Charlottesville, Virginia, and says "FYI - we're not a Passive House (we're close)...just playing along." It's pretty cold there, and his house dropped about 6 C in 54 hours; that's pretty good, but that is still significantly more than we are seeing in the certified Passive House buildings, I think a good demonstration of why one should really try to go for the true Passive House numbers. Engineer Martin Gillie's house is probably like my own; in not very much time, the inside is just about the same as the outside, and you have to dress for winter. As he notes, "You lot may have a point...!" John Butler is a certified Passive House consultant, but he doesn't live in one. Like me, he wishes he did. Because we all learned something from this. It was such an interesting coincidence that this challenge started just after the worst of the cold weather in Texas, where people have suffered so much. Everyone participating in the Passivhaus Challenge has the option of turning on the heat, or even cooking a roast, but the challenge clearly demonstrates that the Passive House approach makes a real difference in resilience. Everyone here was having a bit of fun; as Mark Siddall tells Treehugger: "Like you, I'm excited to see how everything is unfolding - everyone is so engaged. It's wonderful to see so many people taking part - not just people that live in Passivhaus homes, but others with modern and older homes....Who could have predicted this would turn into an event that so clearly demonstrates how Passivhaus homes perform?" The real lesson here is that every home should be built this way. No doubt some people would complain that it is too expensive, but one only has to read the news to see what the costs are when you don't.