Saving Organs. Saving Lives.

Passive House Standards: the Minimum for Housing Now

The Irish Experience:

Building the Toronto Difference

Seasons in a Passive House

Illustrations by Michael Eddenden

Winter

It’s a bitter morning. I’m admiring the icy frost on the exterior windowpane. A cup of tea in one hand, tracing the delicate patterns with the other, I feel toasty warm sitting—I might as well admit, in the cat’s window nook. It’s a tug-of war. I can sit here only if I move Angus first, usually several times. It’s comforting to know the kitchen’s warmth does not leak through the triple-glazed windows as proven by the frost buildup. In my old house the walls were too shallow for a window seat and there was condensation and fogged glass on the window.

Having a completely silent home has made my new routine a joy to perform. I have taken up yoga for my New Year’s resolution and the absence of a furnace constantly turning on and off means my space remains peaceful. Putting my hand against one of the air grills, I feel a soft puff of air. I remember when I would have drowsy bouts late in the day in winter, cocooned at home. Yet these past few months, although I have stayed indoors, I feel refreshed from the constant fresh air in every room. No stuffiness. No stale air. I feel as though I’m getting healthier—more oxygen, with every breath.

The dry winter months play havoc with my appearance; from fly-away hair to scaly skin. Breathing dehydrated air also increases my vulnerability to asthma, bronchitis, sinusitis, and embarrassingly, to nosebleeds. It was frustration with all this—with modern homes dependence on machinery, furnaces and air-conditioners, that coerced me into considering a Passive House. Like other North American architects I was vague on the science; it was an eco-buzzword floating around the office. European. Now we, Kearns Mancini, are experts, proselytizing the concept, and the building code is set to adopt the principles.

It was the energy recovery unit, the regrettably named ‘ERV’, that solved my air quality problem. In winter, heat and humidity is transferred from the warm and moist air inside to the supply air—the cold, dry air coming from outside. In the summer the reverse happens: heat and moisture from the air outside is transferred to the exhaust air stream, leaving supply air coming into the house that is cool and fresh but without the humidity.

Last week we had a power outage. Three days of high winds meant the power grid could not be fixed. This was the ideal test of the super-insulated walls. Outside the temperature plummeted, dropping below -18˚C, and all I thought was: how cozy, how airtight, the house felt.

Spring

Daffodils signal spring. Rain too. Next will be the leaf buds forming on the maple and cherry branches. Just outside the west facing windows, the deciduous trees we planted will form a canopy shading the setting summer sun and blocking the afternoon heat before it passes through the triple pane windows. It will cast the perfect light for writing. By orienting the building with the sun’s travel, planting trees as natural shading devices, and keeping the building design compact, our home is the embodiment of what I deem Intelligent Architecture.

The season of growth brings the excitement (work) of gardening. I have taken advantage of the two-foot thick walls (R-60 insulation) to place my seedling trays in the deep window nook. It’s generous. There’s room enough to accommodate my potted plants: herbs and flowers.

These can be the cruelest months too. Seasonal allergies keep me indoors on days with high pollen counts, days spent avoiding the outdoors—especially in this house. There are HEPA filters in the ERV unit. They clean the incoming air far more thoroughly than the filters in the other houses I have lived in, those that had filters. This house is a relief. My symptoms are mild, I require less medication, and I sleep better. The ERV purifies the “lungs” of my home.

My unit was designed with an open loft above which I have adopted as my home office. I was concerned that it would be hot and stuffy; warm air rises. However, the ‘vertical temperature gradation,’ as the technical minded term it, was minimal. Due to the constant flow of air the loft remained…pleasant. Any heat build-up generated by multiple computers was dissipated with the constant movement of air. It wasn’t just an office, but a retreat. So much so, my son added his desk. I’ve often found we work together now. His interruptions with the latest Reddit trivia can be trying but I get to see what homework he does.

One of my spring-cleaning tasks is window washing. In addition to the benefits of the window’s high thermal performance, their tilt-and-turn operation provided easy access for a thorough clean. The windows open inwards so they can be cleaned from inside. The window’s tilt position is ideal for ventilation. And borrowing the fragrance of the blossoms.

Summer

It was July of 2019, when my husband and I moved into our six unit passive house building. Our decision to choose a Passive House was three fold:

1. To be our final house, if possible. Long term ownership. A robust home built to “Age in Place”. I intend (hope?) to pass this home to one of my children.
2. Health benefits of an oxygen-rich, constant clean air supply.
3. Our decision to live lightly – reduce greenhouse gases.

Summer is unfortunately the season of road construction and my neighbourhood was one of the slated projects this year. However, closing the windows vastly reduced the noise. The acoustic performance of the triple-glazed windows even blocked out the raucous kids at the adjacent pool party. And the cannabis smoke, although that wasn’t due to the windows. Following our week vacation in August, we returned home to a pleasant surprise. I had expected the typical musty smell after our old house had been sitting empty and shut down for a week. Our home was exactly as we had left it, a clean fresh scent. No trace of the smoke. The ERV has an option to set on Holiday mode, with minimal air circulation.

It also works well in Party mode. When we arrange our potluck get-togethers, we let the cool morning air blow through before closing the windows and set ‘ERV’ to Party mode (High). Without air-conditioning we were cool. A meter monitors the CO2 level. When, as more people show up, the CO2 level rises, ‘ERV’ ramps up circulation.

Generous overhangs above the windows block the intense summer sun when it is high in the sky, but without a loss of natural light. Daylight remains abundant. All the living spaces face south and fill with it. During these long summer days we use fewer lights now, and they aren’t on as long, saving money. And cooling the house. Grouping the habitable rooms along the south face also benefits ventilation. The living room and bedrooms are supplied with fresh air 24 hours a day while stale air is exhausted from the service rooms, the bathrooms, laundry and kitchen. It’s just being practical.

Fall

During harvest, I’m more adventurous with my cooking. I want to try new recipes and sample foods from different cultures. Perhaps fortunately, with the constant ventilation, even smells of stir fries and curries are quickly eliminated. A kitchen in a Passive House doesn’t even require a standard exhaust hood above the stovetop, as the room’s exhaust vent is sufficient to dissipate the steam and odors. Continual air movement has other unlooked for advantages. I sometimes design our meals around the efficiency of the home’s temperature balance. On cooler days I put a roast lamb or stuffed squash in the oven, or use the slow cooker because they generate heat.

In October the temperature dropped, but we were able to use all the rooms as they were meant to be used. Angus kept to his favourite spot curled up on the window seat. Claiming his space. Napping on and off in the sun, he watched the birds. Even though the windows open they are airtight when shut. Even the patio doors are free of drafts. There was absolutely no thermal bridge along the edges of the still warm concrete floor.

Preparing for the upcoming winter in the past involved a yearly furnace maintenance: inspect heat exchanger, clean pilot, check gas line and shut-off valve, check fan switch, and so on. With a Passive House ERV, the only maintenance needed was replacing the HEPA filters. In my previous house, Fall meant cleaning the numerous air vents installed in the floors, walls and ceilings, an unnecessary chore in a Passive House.

November’s Utility bill arrived—I was thrilled! A 90% reduction! Because our South facade has 30% window area, 60% of the home’s heating comes from the southern sun. The low-angled winter sun adds heat to the inside, and the thick walls let barely any of it escape. It was a reminder how easily it would be to take all this for granted: one only notices how comfortable a home is by absence of that comfort, too cold or too warm, and drafty. I could say the same about other aspects of Passive House life, such as the missing odours, or the lack of noise, whether from outside or from the mechanical drone of machinery inside I’d always accepted as unavoidable in other homes I have lived in.

COVID-19: How Passive House = Passive Health

Researched and written by Kearns Mancini Architects Inc. 

Across the globe wildlife is reclaiming its natural habitats; dolphins in the Italian canals, foxes in Toronto, deer in the streets of Japan and penguins in the suburbs of Cape Town. We, the humans of the world, would also like to return to our cities. But how do we do that safely amidst a pandemic?

The way our cities are designed are expressions of the people who inhabit them, and throughout history pandemics have had an impact on how those expressions are implemented. Paving streets with flagstones became popular because there was a desire to seal in poisonous gases from the earth that were thought to carry disease. London’s impressive sewer system and New York’s Central Park came to be because of cholera. Tuberculosis, in part, drove the cleanliness of modernist interiors. Now, in 2020, the world is learning how to mitigate the effects of COVID-19, the new form of Corona virus causing respiratory illness. We’re beginning to question what our buildings are doing to help or are they in fact aggravating the problem?

Background

In the last 300 years there have been approximately three influenza pandemics in each century so we can safely assume they will continue to occur. In an increasingly urbanised world, frequently confronted by such challenges, it is important that cities are resilient enough to respond efficiently, especially when humans cause the disease to spread. Like most other viruses, it is commonly understood that COVID-19 is transmitted by means of respiratory droplets that become aerosols, tiny particles generated by coughing, sneezing, shouting, and to a lesser extent, singing, talking and breathing.

People and Buildings

Buildings can either support or suppress our immune systems. Beyond the effects of COVID-19, recognizing that buildings have a constant effect on our physiological health is important because ordinarily a form of Corona virus accounts for 15% to 30% of common cold flu’s. Moreover, almost all global pandemics (Spanish Influenza, Ebola, SARS and MERS) have come from viruses, the leading cause of respiratory tract illnesses.

Under normal circumstances North Americans typically spend 89% of their time indoors. During this pandemic however, that number is considerably higher as we are forced to rely on buildings that enable us to recover, self-isolate or practice physical distancing. Considering our daily intake of fresh air falls between 11 000 to 15 000 litres having clean indoor air to breathe, especially when isolating inside, is of paramount importance.

Sick building syndrome (SBS), a term coined by the World Health Organization (WHO) in 1986, is a condition commonly affecting office workers where poor indoor air quality (IAQ) was found to cause respiratory problems, amongst other symptoms. During a pandemic where our respiratory systems are already under attack, we should not have buildings that make it worse. Due to its’ geography, Canada may be particularly susceptible to rapid virus spread.

Illustration of sick building syndrome by KMAI

Infectious diseases display distinct seasonal patterns in temperate climates like that of Canada. The Canadian population mostly inhabits a narrow east-west (30-50^oN) corridor where COVID-19 has had significant community spread in cities and regions at consistently similar weather patterns; most notably low temperatures and low humidity.

Source: ClimateReanalyser.org. Climate Change Institute. University of Maine.

It has been verified that cold, dry air contributes to the spread of respiratory illnesses. It is interesting to note that the virus did not spread aggressively to countries immediately south of China but locations where significant community spread did occur, had a fairly dry indoor humidity level in the weeks prior to the outbreak. This can be attributed to the fact that the dryer the air, the more droplets evaporate, the longer the virus survives, the further it travels and the more people get infected.

In warmer climates, air conditioning used for cooling may exacerbate conditions as it tends to lower the relative humidity of the air. Overall, the effect can be countered by raising the moisture level inside our buildings. This is known as increasing the percentage of Relative Humidity (RH).

Relative Humidity and Buildings

“Relative” means “compared to“. RH is the amount of water vapour compared to a specific air temperature. It is expressed as a percentage and the higher the percentage, the more moisture the air holds. Air, regardless of its temperature, has to maintain enough water vapour to be safe to breathe.

Illustration of Relative Humidity by KMAI

Traditionally we heat our buildings during winter by taking cold outside air, with a relatively low moisture content, and heating it to a comfortable temperature indoors. Heating the relatively dry air without adding any moisture deprives the air we breathe of the water vapour our body needs to function properly. The RH inside a space affects the rate of evaporation of moisture from our skin and causes sensations such as dryness of mouth, nose and eyes (where the mucous membranes are found that transport COVID-19). This comparatively moisture-free air then provides a clear path for airborne pathogens to enter our bodies.

Illustration showing how RH drops when relatively dry winter air is heated in buildings without adding moisture, by KMAI

In 1987 the WHO published results on the possible health risks associated with cold temperatures in a study titled Health impact of low indoor temperatures. In 2007 lab experiments confirmed that cold temperatures and low RH are favourable to the spread of influenza viruses, but concluded that surveillance data was necessary. Since then a growing body of research has proved that low RH leads to increased spread of influenza viruses.

What is unique about pandemic viruses is that they replicate deep inside our lungs. When our cells detect this, they trigger a strong immune response which leads to an influx of fluids into our lungs and it restricts the capacity of airspace we have to breathe. Inside the body mucus needs to be moved to promote clearance of pathogens that enter the respiratory system. Research has shown that lower temperatures are associated with a reduction of mucus movement, disrupting the body’s mechanical defence and immunity towards infection. The low humidity makes the mucus difficult to move.

The effect of low RH on human health is two-fold; not only does it negatively affect the immune system, but low relative humidity has found to aid in the survival and transmission of viruses. Influenza viruses are five times more infectious at a lower relative humidity because the droplet crystallizes and the stability of the virus is maintained which makes propagation in nasal mucosa easier. In addition, dry air encourages evaporation and reduces the size of aerosol particles, making them easier to transmit because they can travel farther in dry air.

Iwasaki. Seasonality of Respiratory Viral Infections.

Mitigating transmission in buildings becomes particularly important because usually low outdoor temperatures result in higher indoor densities. Research specific to Canada, which evaluated data from Toronto over a five-year period, found that a RH range of 50% to 60% is where the least amount of transmission occurs. Canadian building operators are advised to maintain humidity levels between 35% and 55% but most fall short of this threshold, especially in colder and dryer climates where it is difficult and expensive to sustain those levels.

There are two reasons for this. Firstly, modern construction focuses on keeping building materials dry, not on the transition of heat/cold through the material. As warm air holds more moisture than cold air, this transition from warm to cold causes water vapour to get trapped inside the material, condense into liquid water and subsequently cause mold growth. Secondly, our current building stock is fairly old and built to satisfy minimum construction codes, that never paid much attention to energy use in building operation.

So how can we effectively manage the moisture levels in our buildings? Clearly it is imperative to get the envelope right to allow for the optimal RH range to be met while also ensuring condensation and mold does not occur.  In the interest of health we need a science-based response to building, so we look to the world’s most rigorous building standard for answers.

Illustration of water vapour condensing into liquid as it moves from hot to cold through the building envelope and causing mold, by KMAI

PASSIVE HOUSE BUILDINGS

Passive House (PH) is an established, reliable methodology originally inspired in Canada in 1977 and later refined in Germany in 1991. It developed as a comfort and health standard with super energy efficiency as a residual result. Today, it is considered a precise, science-based energy performance standard that uses functional requirements to deliver incredibly high levels of comfort, health, energy efficiency, durability, and resiliency. This meticulous approach to design and building, simultaneously minimizes operating energy by 60-80%, with space heating and cooling demand reductions of roughly 90%, whilst maintaining impressive indoor thermal comfort levels. The standard has a fabric first approach with critical emphasis on air tightness (that reduces energy leaks), a heavily insulated building (minimizing heat transmission/losses), a mechanical ventilation system with energy recovery ventilators (producing the highest level of indoor air quality), and heat recovery (allowing for heating and cooling systems to be used when if and when needed).

PH design and construction is built on 5 principles that minimizes heat gain or loss and is shown in the figure below.

Illustration of the 5 principles of PH, by KMAI

 One of the many benefits of PH is that a powerful ventilation strategy gives the building operator enhanced control over the indoor air quality. Managing the level of RH needed for healthy environments becomes easy. However, simply increasing the RH of an indoor space does not solve the problem because too much moisture in a building causes fabric degradation that also leads to various human health problems. Special attention needs to be paid to a safe range of RH, avoiding building degradation and ensuring occupant health.

Providing for a tighter range of humidity (40-60%) can mitigate pathogens without causing other adverse effects. This is shown below as the “optimum zone”.

Source: ASHRAE HVAC Systems and Equipment Handbook, Chapter 22. 2016.

Most governments currently set indoor air quality standards with regards to temperature, fresh air introduction and limiting pollutants, but no specific standards have been set for RH. Mandating a minimum indoor humidity level in buildings should be considered as it can help save lives.

The spread of infection can be accelerated or controlled by heating, ventilation, and air conditioning (HVAC) systems. In fighting COVID-19, public health doctors have continually emphasised the importance of introducing fresh air in the building.^20;25 Balancing heat and moisture inside a building requires a proper ventilation strategy as well as a controlled, tight envelope – like a balloon. PH buildings are designed according to building physics where a constant balance exists between the envelope, HVAC system, and air tightness.  All potential design conditions are tested and qualified to satisfy these interior/exterior conditions so that the HVAC system can properly maintain constant fresh air and adequate levels of RH.

The American Society for Heating Refrigeration and Air Conditioning Engineers (ASHRAE) has recommended 4 ways a proper ventilation strategy can help mitigate the pandemic. 1) Set RH and temperature targets, 2) Filter the outdoor air coming into the building, 3) Dilute the air inside the building by bringing in more outdoor air, and 4) Purge the air in the building. In ASHRAE’s recent position document on infectious aerosols, they focus on three ways to manage airborne pathogens with a mechanical system: trap it (filtration), kill it (disinfection), or flush it (ventilation).

They recommend improving the central air filtration system by using MERV-13 filters but state that flushing the pathogen by increasing the amount of outdoor air whilst increasing the air change rate, is the most proven approach to reducing unwanted airborne particles. To ensure the success of these two approaches, ASHRAE further recommends running the mechanical systems for longer periods of time, 24/7 if possible. More stringently however, the Federation of European Heating Ventilation and Air Conditioning Associations (REHVA) recently called for engineers to stop re-circulating air in buildings in areas with a COVID-19 outbreak.

These steps are not common in traditional building operations because they place a massive demand on energy use and consequently, costs. This is why following the PH standard is extremely beneficial; it targets 3 of ASHRAE’s recommendations by default. Not only does PH require MERV-13 filters as the standard in their ventilation systems, no air is re-circulated in a PH building and the ventilation system is mandated to run 24/7. Moreover, the dramatic increase in heating demand caused by constantly bringing colder fresh air into the building is countered by the high efficiency heat/energy recovery system mandated. In conjunction with the ventilation system the airtight, insulated envelope removes infiltration and exfiltration, thereby eliminating the need for any make-up air units. This maintains superior air quality resulting in a consistently healthy environment.

CONCLUSION

We should be cognisant of the fact that weather alone, such as an increase of temperature and humidity during summer months, will not necessarily lead to lower case counts without the continuation of extensive public health interventions. As builders, architects, operators, and owners we have the responsibility to advise and help improve public health. Cities are made of people and any effort to design resilient, sustainable cities must therefore take into account the social contexts of urbanism. Safety is a basic human right and buildings should ensure safety, not hinder it. We should realize the massive health benefits that can be unlocked by building better.

Passive House presents a wonderful opportunity to build better, create healthy environments and future-proof our buildings simultaneously. This standard has the ability to respond to COVID-19 while not ignoring climate change as the systems it employs allow for a total building design where environments are healthier, energy is saved, and emissions are avoided. Passive House is the easiest, most defined way to achieve Net Zero Carbon and Net Zero Energy.

***It is important to keep up to date with new information on Covid-19. The way in which this research was presented was accurate as of June 2020.

Acronyms:

SBS – Sick Building Syndrome

IAQ – Indoor Air Quality

RH – Relative Humidity

PH – Passive House

HVAC – Heating Ventilation and Cooling

ASHRAE – American Society for Heating Refrigeration and Air Conditioning Engineers

REHVA – Federation of European Heating, Ventilation and Air Conditioning Associations