Next stop in our new series on retrofitting older homes: changes to attain Passive House standard. We have received many requests from readers on how to transform an existing home into a passive home.
Everyone who follows this blog is aware that our mission is to build passive whenever we can. Building to PassiveHouse standard makes the home environment healthy, therefore translating into healthy living. It also makes the world a much healthier place as our dependency on petroleum-based fuels as heating and cooling sources is removed. Finally, a passive house is much cheaper to run. You can think of a passive house as the domestic equivalent of an electric vehicle.
EkoBuilt follows the guidelines from the International Passive House Association. There is a lot of building science behind passive, so it can get very complicated, but it can also be explained and understood very simply. From a build perspective, the world is slowly transforming to become completely passive. Certain areas of British Columbia already mandate the passive standard in order to qualify for a new building permit. It’s important for everyone to understand as it will be here in Ontario sooner than we think.
Why does passive house exist?
It’s simple: to replace heating and cooling dependency on gas with electricity. That said, this is only economical if the heating/cooling demand can be reduced to a point where it’s inexpensive to use electricity, and this is where design essentials come into play.
There are three essential design features in a passive home:
It’s vitally important that heat loss is minimized through unwanted and unnecessary leakage of air. We conduct what’s called a blower door test to find the ACH (air changes per hour) a home experiences.
Most newly built homes experience ACH anywhere between 3 and 5, meaning 3 to 5 times the entire volume of air inside the home escapes each hour. This is basically a loss of heated and cooled air which can also result in condensation in the wall cavities, translating ultimately to unhealthy mold.
For newly built passive homes, the ACH rate is 0.6 and the retrofit standard is 1.0.
Old school thinking favoured this air loss, thinking it good for fresh air to enter the building and provide a natural fresh air environment. We now know this is laughable because of all the mold problems we’ve heard about with older homes. To be fair to the old schoolers, in the past, modern building techniques/methods did not exist, nor did heat recovery ventilators (HRVs), so the options didn’t exist to change this approach.
Modern building code recognizes this fundamental change. For example, since 2017 Ontario building code has made HRVs mandatory in all homes, which we were thrilled to see happen. The problem is the HRV is only required to be 50% efficient and most homes are still leaking more air than they should.
2. Thermal envelope
Currently new-build homes, according to the standard building code, are required to have R22 wall insulation, R32 roof insulation and R10 below slab insulation. By comparison, in our local area, newly built passive homes require R75 wall insulation, R110 roof insulation and R40 below slab insulation.
As a general rule of thumb, homes retrofitted to passive standard require R48 wall, roof and below slab (or floor) insulation.
3. Proper windows
For thermal comfort, it’s very important that a passive approved window is used. These are triple glazed units with insulated frames equivalent to an R12. This may not seem like much, but compared to a non-certified triple glazed window, it’s huge. With non-certified units, it’s hard to find a unit above an R4 rating.
Certified windows optimize comfort by having a high temperature interior pane (instead of being cold on the inside when it is cold on the outside). In the passive scenario, this means when it is 25°C outside, the interior pane must be at least 17°C. Non-certified triple glazed windows can be as low as 12°C on the inside under the same conditions.
For those who would like the complete building science, please have a look at the following 20-page document, Criteria for the Passive House, EnerPHit and PHI Low Energy Building Standard (pdf). You can also view four charts at the end of this article.
How can an older home become Passive?
With all of that out of the way, how does an existing home reach the Passive standard?
To be achieved in the most cost-effective manner, this approach will obviously vary depending on the home in question, but some general rules apply:
For the walls: Airtight/vapor tight permeable layers and extra insulation will need to be installed. This will mean that either the interior or exterior finish will need to be removed (the choice will usually depend on which is most cost-effective). Certified windows and doors will also be sourced.
For the roof: If the home has an attic space (most do), extra insulation will be added to that space with an airtight/vapor tight permeable membrane installed on the ceiling side. If there is no attic, then an extra thermal later will have to be installed on the interior. If the ceiling is cathedral in design, it should be simple to build the ceiling down to the required R value. If the ceiling is flat and losing height is an issue, than a vacuum panel will be used to provide a thermal barrier with minimal loss in ceiling height.
For the slab/floor: If a basement is unavailable/unusable, then a thermal layer will be added to the existing floor cavity. If a basement is present and usable, a vacuum panel will be used to provide the thermal barrier with minimal loss in height.
Interested in making your existing/older home Passive? Give us a shout, we’d love to help you realize that goal.
You may also be interested in our blog post on taking a staged approach to retrofitting your older home.