Passive House: Climate-Proofing Against Disease and Smoke

Photos by Jakayla Toney, Canva, and Kelly Sikkema

2021 has been an unforgettable year. The Covid-19 pandemic is still raging across the globe, and this summer, atypical floods hit China and mainland Europe while historical droughts and wildfires decimated North America. In Canada, wildfires burnt small towns to the ground while choking urban centers, drought destroyed crops across the Prairies while causing water rations across the country. The impacts of climate change are here and now and in our back garden. In fact, after a summer of wildfires and smoke alerts, a shocking study reported that 86% of Canadians live in areas where air pollution exceeds WHO guidelines.

More than 70,000 scientific papers have examined the relationship between air pollution and our health, many of which cause grave concern. These studies translate into reality as air pollution contributes to 15,300 deaths per year in Canada. The general public is starkly aware of iconic air pollution sources like car exhaust fumes or industrial chimney stacks but rarely fret over the air quality in their homes despite Canadians taking 9 out of every 10 breaths indoors.

Covid-19 has shaken the world in many ways, particularly bringing our attention to indoor air quality. Many public spaces and homeowners scrambled to implement strategies to mitigate covid-19 transmission indoors - but this article will not examine Covid-19 and IAQ as PBC has already covered the topic. Instead, as 2021 heavily featured climate-induced flooding and drought, we will discuss the potential for such events to influence indoor air quality and impact occupant health. So, is the air in our homes and buildings killing us? Is climate change making it worse? And, are passive buildings an obvious solution?

Moisture

A microbiome is a collection of organisms in an environment. Each person has a unique microbiome, almost like a fingerprint, which we spread around the spaces we frequent. The delicate balance of microbes on our skin and in our homes is mostly beneficial as they stave off disease and infection. While humans are the dominant source of microbes for indoor environments, moisture and air intrusions bring foreign organisms inside. Such intrusions come from leaky walls, windows, door frames, roof joints, and events like flooding. This increases moisture levels indoors, where pathogens and mold can reproduce. Inhaling mold or bacterial pathogens has adverse health effects ranging from allergic reactions to lung disease.

Photo by Jezael Melgoza

Current climate models show that rising global temperatures will alter the Earth's water cycle, resulting in more intense and frequent precipitation (rain) and storm events. Unfortunately, these events will increase indoor moisture values, disease-causing organisms, and antibiotic resistance, particularly in urban areas laden with impermeable surfaces. In addition, research shows that increased levels of pathogenic microbes occur even after remediation efforts to sterilize the indoor environment post-flooding.

Notably, air tightness in passive homes also prevents structural damage rendering them more durable than code-built houses. With climate change causing vast fluctuations in average precipitation and humidity levels (i.e., wetter winters and dryer summers), it is essential that the building envelope is sealed correctly to prevent mold and rot within the integral structural components. Passive buildings are built to meet the highest air tightness standards, rendering their envelopes less susceptible to moisture intrusions compared to code-built houses (PDF). This means passive houses will protect occupant health by controlling moisture in buildings that will last longer during climatic changes.

Wildfires

Photo by Marcus Kauffman

The impacts of wildfire on air quality may be more tangible when compared to flooding and heatwaves. In 2021, wildfires raged across Canada and the USA, compounding smoke levels left urban centers like Vancouver and Toronto with the worst air quality in the world. While Environment Canada issued alerts for high-risk air pollution levels, they advised staying indoors and limiting time outside. Air quality alerts for wildfire smoke began in June 2021 and are still being issued for parts of the country now (October).

Research shows that wildfires negatively impact indoor air quality (IAQ). For example, one study conducted in Washington state showed that during smoke inundation from wildfire, indoor particulate pollution levels ranged from 4 to 22 times the EPA 24 hour threshold for human health and welfare (PDF). In addition, a plethora of research shows that particulate matter (released from wildfires) causes chronic health impacts and impairs cognitive function.

The Passive House Solution

For decades HVAC systems have been mandated in health care facilities and government buildings. These systems combine air filtration, purification, dilution, and humidity control to mitigate indoor pollution and improve air quality. However, traditional HVAC systems are not fully equipped to deal with particulate matter from wildfires or flooding. While adding a HEPA filter to screen these tiny PM 2.5 particulates is usually an option, the original system must compensate for pressure drop and resistance by increasing energy demand. This decrease in efficiency is not ideal given the associated energy costs and GHG emissions.

Photo by Meritt Thomas

The passive house standard utilizes a combination of airtightness and mechanical filtration to provide air quality that is better compared to conventional buildings. Passive house buildings are designed to be airtight but moisture permeable allowing moisture to escape while preventing air from leaking out. Stale air is vented out, and fresh filtered air is brought in through a heat recovery (HRV) or energy retention (ERV) ventilation system. This approach prevents (or reduces) contaminated air and moisture from entering the home and reduces the opportunity for pathogen growth and particulate matter in the house. While different systems are equipped to filter various particle sizes, selecting a filter with a higher MERV rating will allow for finer filtration.

While the impacts of moisture and smoke on occupant health is a well-explored field, the effectiveness of passive house standards to protect its occupants during wildfire and flooding is still being explored. Evidence suggests that airtightness in passive homes reduces smoke concentrations by 30% compared to code-built homes during wildfire events. While particulate matter levels were still beyond the safe threshold, it was noted that smoke entered through the standard ventilation system, which could be reduced by installing finer filters (“HEPA filters can capture over 90% of smoke-sized particles”). Other sources suggest that high-quality HRV's and ERV's filter down to 0.3 microns which encapsulates wildfire particulate matter without additional filtration.

Passive buildings have long been known for their ability to reduce energy consumption and costs for the owner. Despite debates over effectiveness, it is also clear that the passive house standard offers more protection against climate-induced indoor air pollution than a code-built house. The Covid-19 pandemic collided with some of the worst wildfire and flooding events seen to date globally, highlighting the importance of a safe and clean indoor air environment and the need for new regulations around safe IAQ thresholds. In addition, passive houses reduce the likelihood of contaminated moisture or air entering the home, protecting the occupants from developing or worsening respiratory illness or cognitive impairments. Rolling out this technology in public spaces nationwide and providing support for homeowners to retrofit or build to PH standards can drastically reduce national medical costs and energy consumption and improve Canadians' overall quality of life.

Articles on the PBC website reflect the views of the author and not necessarily those of PBC.