Got a question? Send us an e-mail at info@cottonwoodpassivehouse.ca!

What are the main features of a Passive House?

A Passive House doesn’t necessarily need to look different than a typical house. Passive Houses are characterized by:

  • Compact form, to minimize external surface area and reduce heat loss
  • Good solar orientation, to capitalize on solar gains in winter
  • Super-insulated walls, floors and roofs
  • Extremely high-quality windows and doors that minimize air leakage and heat loss while actually providing solar heat gains. They are net energy producers!
  • Fantastic indoor air quality due to continuous ventilation provided by a heat recovery ventilator (HRV). See below.
  • Very steady indoor temperature throughout the year. You can sit next to the windows in winter in a T-shirt and not feel cold. In the summer, Passive Houses are only allowed to be over 25ºC for 10% of the year.


Why would I want a Passive House?

Most people who decide to build a Passive House are drawn to the extreme energy savings first. But there are other benefits, as mentioned above: low operating costs (as a result of using less energy), high indoor air quality, and great thermal comfort. Passive Houses are simply higher quality buildings. For the story of the Cottonwood Passive House, read this post to learn why Jim and Emilie Zeibin wanted a passive home.


What’s the payback on a Passive House?

People are hard at work trying to understand the premium currently required to build a Passive House in Canada. Many factors influence this extra cost: the local climate’s impact on energy demand, skills and knowledge of local tradespeople, availability of Passive House-quality components (window, doors, HRVs, etc), and so on. Generally, Passive House builders are finding a premium of 10-20% is required. This number is expected to drop as the market for Passive Houses matures. Given our extremely low cost of energy in Canada, the payback time can be quite long, especially in cold climates where greater initial investment is needed. It’s important to remember that quality always costs extra money. As Guido Wimmers, Director of the Canadian Passive House Institute, has said, “No one asks what the payback is on a Mercedes.”


What’s the difference between Passive House and Net Zero?

Passive House and Net Zero are totally compatible concepts. Net Zero just means that you are producing enough energy on site to cover your energy use — usually producing more than you need, feeding extra energy back into the electricity grid. However, the lower your energy demand, the less energy you need to produce. This is where Passive House comes in: focusing on energy conservation and efficiency first, before adding the “active” systems such as photovoltaic panels or wind turbines. “Passive” features like extra insulation and high-quality windows and doors generally require little or no maintenance, whereas active systems require ongoing maintenance and likely have a finite lifetime before they need to be replaced.


What is a Heat Recovery Ventilator (HRV)?

An HRV is a piece of mechanical equipment that extracts heat from air being exhausted to the outdoors, and transfers it into incoming air. HRVs in Passive Houses are the heart of the mechanical system and are required to be at least 75% efficient, though in practice efficiencies of 85% are more typical. This means that if air is leaving the house at 20ºC, the incoming air can be pre-heated by the HRV to as high as 17ºC before needing any additional heating.

HRVs are becoming increasingly common, so expect to hear more about them. Vancouver already requires all new houses to be equipped with an HRV.


When you say “airtight,” what do you really mean?

Passive Houses need to be tight to avoid losing warm air to the outdoors (and prevent cold air from coming in from the outdoors) through cracks in the building envelope. This is called exfiltration and infiltration, respectively. Exfiltration is not only a concern regarding temperature, but also as a mechanism for water vapour in warm, moist indoor air to enter the walls/floors/roof where it might encounter cold surfaces and condense into water, which can cause big problems. Passive Houses are required to meet a stringent 0.6 ACH (“air changes per hour), which compares to about 2-3 ACH for typical construction — maybe 1.5 ACH if the construction crew is paying attention and knows what they’re doing. (The R-2000 building standard in Canada requires 1.5 ACH.)

To keep the indoor air quality high, the HRV runs constantly at a very low air velocity and is sized to completely replace the building’s indoor air approximately every 3 hours. Supply air vents are provided in regularly occupied living spaces (living room, bedrooms, etc) and extract air vents are located in bathrooms and service spaces (kitchen, storage room, mechanical room, etc). The system is automatically balanced (incoming air = outgoing air) to avoid pressurizing/depressurizing the house.


With such an airtight house, aren’t you going to have humidity problems?

The HRV (Heat Recovery Ventilator) runs 24/7, extracting heat from the house’s exhaust air and transferring it into the incoming air supply. The HRV is sized to provide approximately 0.3-0.4 air changes per hour, which means the entire volume of the house’s air is replaced about every 3 hours. In cold climates (like Edmonton), the outdoor air is very dry, containing very little moisture. With such high air turnover, dehumidification of the indoor air is actually the concern, to the extent that it’s often recommended that the HRV be fitted with a humidity recovery device to extract humidity from the outgoing airstream. These are sometimes called ERV’s (Energy Recovery Ventilators).

It should be noted that kitchens and bathrooms in Passive Houses are the main sources of humidity. A booster timer is usually installed in these rooms so that occupants can manually increase the ventilation rate during high-humidity activities such as cooking or having a shower.


Won’t the Passive House be impossibly hot in the summer?

One of the less-advertised criteria for certification is that the indoor temperature should not be more than 25˚C for 10% of the year. Passive Houses can use a number of strategies in the summer to stay cool:

  • Shading devices on windows to block high summer sun, but allow low winter sun. (This is the oldest trick in the book in passive design!)
  • Operable windows in all living spaces
  • Running the HRV in “bypass” mode, which means no heat recovery is done but you can quickly turn over the indoor air
  • Mechanical cooling equipment, such as a “mini-split” heat pump/air conditioner in a room that seems particularly prone to overheating
  • It’s kind of hard to imagine in a house, but remember that insulation also works in reverse: keeping heat out of a cool interior, just like a refrigerator.

The Cottonwood Passive House is currently modelled with just 6.1% overheating using a summer bypass mode on the HRV and operable windows for night-time cooling and cross-ventilation. However, we’re still a little unsure how the living room and kitchen will perform in the hottest part of summer after blinds are installed, and so have reserved a spot for a mini-split heat pump should it be needed.


I don’t think Passive House is for me, but I’d still like to make my house more energy efficient. What should I do?

You can still make a big impact on your energy use by focusing on a few key areas, which happen to be main Passive House features:

  • Increase the amount of insulation. In a new build, this means thicker wall assemblies for more insulation, which is probably the best bang for your buck. Roof trusses with raised heels can allow a few extra inches of roof insulation. And installing insulation under the basement slab and on the outside of concrete foundation walls can go a long way. Retrofits can often be accomplished by adding rigid insulation to the outside of the walls.
  • Use high-quality windows and doors. Windows and doors are major sources of heat loss. Good quality construction with good seals and triple-glazed glass are extremely important.
  • Make the house more airtight. This is a tricky one to retrofit, but it can be done. However, be aware that as the house becomes more airtight, the importance of proper ventilation increases. You may need to consider adding an HRV to ensure suitable ventilation rates as the envelope airtightness increases.

If embarking on a low-energy new build or a retrofit, it’s worthwhile hiring a design professional and/or builder with relevant experience as there are a number of interacting factors in these types of projects.