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Too Hot to Handle: Problems and Possibilities With Passive House and Extreme Heat

Sunkissed summer days are a relief for many who experience the long, wet, windy, and bitterly cold Canadian winters. Beaches and lakes are dotted with relaxed city folk, restaurants and bars spill out onto the sidewalks, families explore winding trails and lush parks while farmers eagerly watch their crops grow - a truly magical time. In June 2021, those sunkissed summer days turned into blistering heat traps, city greens perished, forests burned, and the air turned toxic.

Photo by NASA

Vast swaths of North America were consumed by a 1000 - year heat dome weather event which was made 150 times more likely to occur due to climate change. Temperature records were broken up and down the American west coast, later traversing across Canada, affecting Alberta, Manitoba, Saskatchewan, Northwest Territories, and the Yukon. British Columbia (BC) was severely affected, with temperatures peaking at 49.6°C in Lytton Village before it was consumed by wildfire.

BC's health officials and weather experts debated the severity of the heatwave while advising residents to stay indoors in air-conditioned rooms, drink fluids and take cold showers. However, with annual average temperatures sitting around 22C, air conditioning had long been deemed an unessential building expenditure - not accounting for climate change, of course. As a result, demand for air conditioning tripled from 10% in 2001 to 34% in 2021. As the days grew hotter, demand for AC soared, stocks quickly sold out, and supply chains were strained.

Some residents sought refuge in air-conditioned public spaces and hotel rooms, but many were forced to rely on cold showers and make-shift fans while indoor temperatures soared above 35C. Many vulnerable populations such as the homeless, impoverished, pregnant, immunocompromised or elderly became victims of the heatwave. In addition, emergency response units were strained by the vast number of calls while working in deadly heat. As a result, an estimated 570-810 Canadians died across the nation from heat-related illness, and the heatwave was deemed the "most deadly weather event in Canadian history."

Photo by Dan LeFebvre

While the heatwave had severe health and mental implications - dehydration, heatstroke, cardiovascular and respiratory complications, depression, anxiety, drowning and food-borne disease - it also strained outdated housing, commercial and public infrastructure. Many activities and businesses ground to a halt, while 15 school districts were forced to close due to their inability to keep children cool and safe. It may seem like upgrading all buildings to have air conditioning units is a simple solution to combat future heatwave events. But, air conditioning is energy-intensive, and when combined with the leaky code-built infrastructure, energy costs and emissions soar. In fact, BC Hydro insists that the estimated 600,000 portable air conditioning units used by British Columbians during the heatwave helped break peak hourly energy consumption three days in a row, capping at 8,516 megawatts.

Can passive buildings and homes help with extreme heat? The short answer is - yes, no, maybe with some modifications. A passive house's heavily insulated and air-tight envelope allows for sustainable thermal comfort all year round - warm in the winter and cool in the summer. It is easy to assume that high insulation levels will make the house unbearably warm in the summer months, but in a temperate or cold climate zone, the house maintains a cool indoor environment compared to a conventional home.

What if you don't live in a temperate climate zone? Temperatures in Ontario are highly variable depending on the season. You are guaranteed winter temperatures starting at 0C, which can drop as low as -30C - Brr! Fast forward a few months to summer, where the mercury averages between 20-30C. While such temperature extremes are not shared across Canada (especially in the West), climate change is summoning unpredictable and extreme weather events more frequently. In regions where seasonal temperatures vary significantly, specific measures like building orientation, heat recovery ventilation and window shading ensure a passive home does not exceed the indoor temperature threshold of 25C.

How well can a passive house protect its occupants during a heatwave? Unfortunately, we can't say as it's still up for debate - some argue that passive homes are great at staying cool in "normal" summer temperatures, but they require efficient mechanical cooling systems for extremes like the summer heat dome 2021. Others have anecdotal evidence stating that passive homes did stay cool during the deadly summer heatwave. In contrast, evidence suggests that the risk of overheating in a Canadian passive house increases significantly from 2020 onwards. So while a passive standard tight air seal, mechanical ventilation, orientation, solar deflectors, and intelligent design is better at protecting its occupants than a code-build home, it may fall short in the worsening climate change extreme heat events.

Photo by Canva

Are earth tubes a solution to overheating in PH?

While passive houses are excellent at maintaining a stable indoor temperature during typical summer conditions, the industry must adapt to cope with future climate challenges, such as the 2021 heat dome. There are additional cooling options available for passive builds, most notably earth tubes. An earth tube is an underground ventilation pipe that allows cooled or warmed air (depending on the season) to flow into the house. While harnessing the free steady temperature of the earth is a great way to maintain a comfortable indoor temperature, the system isn't typically considered cost-effective and must be carefully designed to avoid hazards.

Condensation, mold, radon accumulation and reduced indoor air quality are concerns associated with using earth tubes. While there are well-documented cases of moist earth tubes contaminating indoor air and affecting occupant health (PDF), these are considered learned lessons for the industry, rectified by environmental scoping, correct design, installation and moisture pumps. In contrast, research suggests that earth tubes effectively keep indoor air temperatures around 17C despite outdoor temperatures reaching 30C. It also showed that these tubes operate without creating conditions conducive to condensation and mold growth. Similarly, evidence from Canada shows that earth tubes maintain the internal conditions of the house even during 37.5C July days.

In contrast, other research suggests while earth tubes reduce a building's cooling load, they are not a replacement for air conditioning in warming climates. Some even insist that the cost to scope and install a tube is unjustifiable and that the inability to clean the pipe will eventually result in contaminated indoor air. While some of these concerns could,