An in-Depth Look Into Passive Houses

Published on November 07, 2018

A Passive House is a home that’s built to a world leading standard in energy efficient construction. This means that a Passive House is 90% more efficient when compared to homes that have already been built, and 70% more efficient when compared to a newly constructed home. Favouring climate change-friendly sources of heating and cooling, a Passive House will often use energy reducing methods such as a geothermal loop to maintain the desired interior temperature.

To achieve Passive House certification, the building must meet a few requirements. The rate at which the building exchanges all of its interior air with fresh air from outside, otherwise known as the Air Changes per Hour @ 50 pascals (ACH @ 50 Pa), must be at the rate of 0.6 ACH @ 50 Pa. This means that in one hour, 60% of the interior air in a Passive House is exchanged with exterior air. In comparison to the 3 ACH @ 50 Pa that is required to meet the current building code here in Ontario, a Passive House is sealed much tighter than a standard, recently built home.

How a Passive House Becomes Energy Efficient

A Passive House reaches its level of energy efficiency through the cooperation of various energy conservation methods. The entirety of a Passive House, (or any house) has to be looked at as a functional system, with each energy-conserving method contributing to the efficiency of the system as a whole. Improving efficiency in one area may mean that supplemental modifications are required to keep the entire system functioning properly.

This is demonstrated through the high level of air sealing and insulation seen in a Passive House, as it lowers the demands put on the heating and cooling systems - meaning that any energy used to condition interior air goes a long way in maintaining interior temperature and comfort levels. This also means that due to the low rate of air exchange in a Passive House resulting from its formidable level of air sealing, a highly-efficient heat recovery ventilation system, as well as a strong air exchange system are critical in maintaining interior air quality. A regulated system for controlling the air exchange in any home that is sealed to Passive House levels, will ensure that the interior air remains fresh by reducing the build-up of airborne pollutants.

With high levels of insulation, strong air sealing, and an efficient heat recovery ventilation system, a home can achieve: a consistent temperature devoid of hot or cold spots, a high level of air quality and comfort, and will consume only a small amount of energy - even in homes that do not quite reach the levels required to acquire Passive House certification.

Attic Insulation is Important!

Just like any home that is looking to conserve energy and reduce the amount of conditioned air that escapes, insulating the attic is of the utmost importance in a Passive House. For example, if the average homeowner had $1000 dollars and was looking to raise their home’s efficiency, installing or improving the insulation in their attic is the best investment they could make; as they will see a return on their investment in only 3 years due to lower utility bills.

In many attics that already have insulation, it is often only installed in between wooden rafters, which only have an insulation level of R-5. These gaps in insulation create a thermal bridge,  allowing heat to easily escape from the building. This means that even in homes with insulation rated at the common R-value of R-20, heat and energy loss through the attic is significant. To markedly increase a home’s efficiency level, or to work towards Passive House certification, a much higher R-value of insulation must be used, in addition to the prevention of heat escape through the attic’s wooden rafters.

Loose fill blown insulation is especially effective at covering all areas where a thermal bridge can occur, as it can insulate places that traditional batts of insulation have difficulty covering. Loose fill insulation is often made from cellulose, which is comprised mostly of recycled newspaper, a fire retardant treatment, and rodenticide to prevent unwanted animal nesting. Due to its environmentally friendly manufacturing process, as well as its cost-effectiveness, cellulose loose fill blown insulation is often the optimal choice for a Passive House.

What a Passive House Looks Like

At first glance, a Passive House looks exactly like any other newly constructed home. Recently, I was testing the Air Changes per Hour of a two story home that far exceeded the Passive House levels of air sealing and insulation. The home had thick, 16 inch walls that were filled with dense pack cellulose insulation, and came in at .22 ACH @ 50 Pa. Other than having deep window sills on the interior, and no basement which allowed for hydronic in floor heating, the house looked like any other home.  

What BSG Can Do to Help Achieve Certification

Determining air tightness levels can only be done by a Registered Energy Advisor conducting an airtightness test. For new homes looking to attain Passive House certification, our Registered Energy Advisors can conduct air tightness tests both during and after the construction process, ensuring that the home has the required air sealing levels, or is on the right track to do so.

For a comprehensive assessment of an entire building, a Home Energy Assessmentcan also be conducted, helping to determine in what ways energy can be conserved. This can include suggestions such as installing high-efficiency heating and cooling systems, or lowering energy consumption through more efficient appliances.