We live in Quebec, and let's face it, winters can be tough. Snowstorms, icy conditions, but above all, temperatures that dip far below freezing.
Picture yourself for a moment into the middle of January:
It's morning, the thermometer outside reads -25˚C. You're dressed in your warmest jacket and sheepskin slippers, and despite the indoor heating being programmed to 23 ˚C, you get the feeling that the air in the house is having trouble heating up. You pass a window. You feel a great chill, as if the window were projecting the cold outside into the house, not to mention the draughts.
Your house certainly seems to have trouble keeping warm.
And you're not alone! Most Quebec homes are inadequately insulated and not airtight enough. It's like going outside on a cold day without a hat, mitts or with a loose coat. The heat inside often finds a way to escape, forcing us to consume more energy to heat our homes. Yet we live in a climate that warrants overcoming these shortcomings to create much more comfortable indoor environments where temperatures are constant; cold radiation and draughts absent.
As a Passivhaus-certified architect, I'm going to explain what the Passivhaus standard is all about and, in a few simple concepts, I'm going to detail the main principles of this type of construction and the benefits you could gain from it.
This brings us back to the question: what is a “passive house”?
A passive house, also known as a high energy performance house, is a type of construction designed to minimize energy consumption and minimize its impact on the environment.
These homes are designed to be highly energy-efficient, offering excellent comfort while requiring very little energy for heating, cooling and lighting.
In other words, as the term implies, the ultimate goal of a passive house is to provide optimal indoor comfort without the need for active heating or cooling systems.
But what are active systems? These are devices that require energy, mainly in the form of electricity, to operate. Common examples include electric baseboard heaters, convectors, air conditioners or central heating systems.
A passive house, on the other hand, uses sources such as solar energy, wind power or even energy generated by the occupants themselves, to achieve the desired level of comfort.
The concept is interesting, but is it feasible?
Feasibility depends largely on climate. In some regions, temperature variations between indoors and outdoors are less pronounced, making it easier to achieve this objective. Cold or arctic climates, on the other hand, pose a greater challenge.
However, a number of recent projects have shown that these objectives are achievable.
There are over 5,000 Passivhaus projects worldwide, mainly in Europe. Canada, meanwhile, boasts over 150 certified projects, including some 30 in cold climates. A third of these are in Quebec.
Clic here for an overview of Canadian projects.
More specifically, what are the objectives or certification criteria for a passive building?
To make the passive house standard internationally applicable, performance thresholds were established in the mid-90s by the Passivhaus Institute (PHI) in Germany.
According to these criteria, the heating demand must be less than 15 kWh/m²/year, or the heating load must be less than 10 W/m². In the case of renovations, heating demand must not exceed 30 kWh/m²/year in cold climates. The same values apply to air-conditioning loads. The standard also includes criteria for air permeability, electrical demand and energy recovery.
To illustrate, a 200 m² (2150 ft²) house should consume no more than 3000 kWh per year, which is equivalent to about $35 per month in heating costs (calculated on the basis of Hydro Québec rates).
The standard therefore leaves room for manoeuvre. A Passivhaus-certified house does not have to be entirely passive. It is possible to install supplementary heating or air-conditioning systems, mainly to ensure a comfortable climate when outside temperatures are extreme. However, the main objective is to design the building in such a way that, in most situations, these auxiliary systems are not necessary.
How do you design a Passive House?
To design a Passive House, it's essential to follow certain fundamental principles.
First of all, not all buildings can meet the Passivhaus standard, and this is particularly true of renovation projects. The standard does, however, provide a specific framework for the latter type of project, to encourage the renovation of existing buildings to achieve better performance. For a building to have the potential to be recognized as passive, it needs to be thought through in advance, right from the start of the project.
This is essential, as the shape of the building has a huge impact on the project's passive potential.
Indeed, the larger or more irregularly shaped a building is, the greater the surface area of its outer envelope. As a result, potential heat losses are also higher.
On the other hand, a building that is compact in form will achieve Passive House criteria much more efficiently. The reason for this is that the greater the surface area of walls/roofs/floors in contact with the outside, the greater the chances of heat transfer, regardless of the envelope's performance level.
Here's a concrete example with different variations for a 200m2 (2150 ft2) house.
The first, very compact volume is a 10mx10m (33' x 33') square on 2 floors. In this example, the surface area of the envelope in contact with the outside is approximately 440m2 (4735 ft2). The 3rd volume is rather large, with a single-story building of 200m2 (2150 ft2) of irregular shape. In this case, the envelope area is approximately 650m2 (7000 ft2). For a similar wall construction, heat transfer in the second case is therefore almost 1.5 times greater! So it's vital to keep the ratio of exterior wall area to floor area very low.
Here's another way to illustrate the same concept:
To maintain the same energy performance, the insulation of exterior walls must be improved according to the percentage increase in the surface area of these walls.
Secondly, the building's orientation is very important. An analysis of the site on which the project will be built is therefore essential. The path of the sun, the direction of prevailing winds, the relief and the presence of vegetation or neighboring buildings will all need to be taken into account in order to maximize their positive impact on the project.
The reason is simple: a passive house wants to maximize its solar gains in winter and minimize heat loss through the envelope. Conversely, in summer, solar gains must be minimized to avoid overheating. Shading devices must be put in place, and natural ventilation is relied upon as a cooling strategy.
In concrete terms, this means that a large part of the fenestration is on the south façade, to let in as much sunlight as possible during the cold season. The north facade, which receives no solar radiation, is opaque to limit heat loss in the northern hemisphere.
The heart of the project, however, lies in the design of a high-performance envelope. This enables the building to better regulate its internal climate by minimizing heat transfer between inside and outside.
Here are the main points to consider for this high-performance envelope:
Super insulation
High-quality insulating materials are essential for maintaining a comfortable indoor temperature while minimizing heating and cooling requirements. Passive houses often use thick insulating material to achieve high levels of insulation.
Design without thermal bridges
Thermal bridges are areas where heat can escape or penetrate more easily, compromising the home's energy efficiency. Thermal bridges occur, for example, when two materials with different heat-conducting properties come into contact. The junction between a concrete wall and a metal window is a good example. Building corners, structural connections and openings in the envelope, such as doors and windows, are often places where thermal bridges can occur. Passive houses are designed to minimize these thermal bridges by designing thoughtful details that enable a continuous insulating link between elements.
Above is an infrared image of a conventional wooden building. Here we can clearly see (in yellow) that heat is lost through the envelope at the wall studs; the insulating value of wood being less than the insulating value of mineral wool.
You can lose up to 25% in energy efficiency for a poor design like this alone.
To remedy this problem, continuous external insulation can be applied throughout the building, creating a thermal break at the structural elements.
Airtightness
Effective airtightness is essential to prevent uncontrolled air leakage, which can lead to heat loss. The Passivhaus standard requires a very strict airtightness of 0.6 air changes per hour (ACH), well below conventional building standards. High-performance air barriers, such as waterproofing membranes and sealants, are used to achieve these airtightness levels. For a renovation project, the requirement is 1 CAH, which is still very low and can only be achieved by removing the existing exterior cladding and replacing or upgrading the air barrier installation.
By way of comparison, a typical 50s building has an airtightness of around 8 to 10 CAH. Once renovated, insulated from the inside with a new vapour barrier and new windows, with no change to the exterior façade, this same building can achieve an airtightness of around 5 CAH. A standard new build, on the other hand, aims for an airtightness of between 2 and 3 CAH.
High-performance windows and doors
Doors and windows are critical in terms of energy performance. Passive houses use double-, triple- or even quadruple-glazed windows, depending on the climate, with insulated frames to reduce heat loss.
However, despite their high performance, windows remain a weak point in the envelope. They will never match the insulating performance of adjacent walls. For this reason, they must be thoughtfully positioned and sized so that the solar gains they provide cancel out heat loss as much as possible.
Together, these elements create a high-performance building envelope that limits heating and cooling requirements, resulting in reduced energy consumption.
Finally, passive houses are also equipped with controlled mechanical ventilation systems with energy recovery (heat and humidity) to ensure high-quality indoor air. These systems are designed to recover heat leaving the house to preheat incoming air. This process helps minimize energy loss and improve the overall efficiency of the HVAC system. Similar concepts can also be applied to the water distribution system.
Make the best of what nature has to offer!
It is by applying all these principles to the design of buildings that better adapted, more efficient constructions, in symbiosis with their environment, can emerge. By increasing the number of projects of this kind, we are helping to build a healthier, more sustainable environment that is less dependent on external energy.
Rather than turning more and more to complex mechanical systems to regulate our indoor climates, it's time to get back to basics and optimize what nature offers us for free!
It's a win-win situation for us all, with buildings that are sustainable, comfortable, energy-efficient and therefore more respectful of our environment. No more feeling cool next to your windows in winter. No more heat loss through leaks, and no more monstrous electricity bills.
So it's time to zipper up your coat, put on your hat and mittens and get ready to face the next Quebec winter well wrapped up. Demand the same from your home!
You have some questions about passive house design? Contact me!
About the author:
Kim Cloutier is an experienced architect with a career marked by projects focused on simplicity and sustainability. She is a certified LEED Passive House Designer and Green Associate, demonstrating her commitment to high standards of energy performance and environmental sustainability. Kim aspires to promote healthier living through her projects, with a focus on creating healthy, sustainable environments.