What are the details and considerations that make a passive house or high-performance house different than a typical building?
In our previous article, What is the Passive House building standard, we introduce you to the program and outline how it differs from building codes and other programs. In this article, we dive a little deeper into Passive House buildings and the top four features and considerations that when combined together create a better building compared to typical buildings.
What is a passive house?
Passive House is a certification system that attempts to design a house that uses less energy.
Using the passive house modeling tool, you can balance many factors in order to meet the criteria. Including R values, window (triple or double, or U value), site orientation, window openings, HVAC equipment efficiency, air tightness, building form, appliances, etc.
All with the goal of getting to 15KWH/m2 of building use per year. Compared to the Ontario Building Code, this is about 30% more efficient than most homes currently being built. I am going to dig a little deeper into some of these items and our approach to balancing priorities in our high-performance designs.
The high summer sun is blocked by the overhang and does not enter the window. The low winter sun shines under the overhang into the window, providing free passive heating.
1. Site Orientation
Like the Passive House building standard, and our approach to building design starts with the project site. We want to make decisions that allow us to take advantage of the sun and wind. Orienting the building to face south is the best way to take in the free heat of the low winter sun and keep out the high summer sun.
We also try to take advantage of natural ventilation to cool the house in the summer based on the prevailing winds and open spaces and paths through the house. Sometimes, this can be difficult where a front yard and street are south, and you likely don’t want large windows for privacy on the street. We have creative solutions for clients who have this site condition.
After we make the key site decisions, we need to decide on the form of the building. Passive House rewards compact building design. For example, a 2000ft2 house on 1 story will have a larger area of wall and roof for heat to be lost. In the passive house calculator, you would need to compensate with greater R values in the walls and roof than a 2000ft2 house over two stories would in the same site.
2. Windows & Walls
Veld architect resource: Wall Types Comparison chart to help determine the best R-value, and construction solution for your house.
After focusing on building orientation and site conditions, we will make some of the technical decisions around walls and windows. Choosing operable windows in order to allow cross-ventilation is very important.
The code minimum of R-values for walls is R24, whereas Passive House states for our climate, the values should be in the range of R50-60+.
This level of insulation is technically more difficult to construct in our current construction industry. As you increase the R-value, you get diminishing returns on energy savings (and also ROI). Therefore, at VELD Architect, we also take an approach of “pretty good,” and there is a sweet spot around R38-44 that can work with conventional building methods and become more cost-effective.
Of course, this won’t get you certified, but it is cost-effective energy performance. Want to dive deeper into window assemblies and the options to consider? See our YouTube video describing the differences between triple and double-glazed windows.
Triple glazed windows PH certified generally perform better at the frames, and tend to be less drafty from a comfort standard. Installing them properly is the biggest factor in determining the leakiness of your house.
Windows in our climate typically need to be triple-glazed in the passive house modeling. We typically advise clients that when you are quoted a U-value of a window, it is generally quoted at the centre of the glass (this is the best-performing location!) However, the majority of heat loss occurs at the frame. So, choosing a good frame is critical and accounted for in the passive house modeling. Generally, the passive house-certified window frames are much better performing.
Regardless of what type of window is installed, the most leaky point of any house is around the windows.
Krista, architect and owner of Veld architect.
3. Airtight Construction
We always show details for contractors to install the windows to a passive house air-tight level of construction regardless of the desire to certify or not.
We recommend posting these construction signs throughout your build to help remind any sub-trades of the unique construction care required.
Of course, we can do all the great things above, but if the building walls and roof are leaky, it doesn’t matter how much insulation you have in the walls. So, making sure that all joints and penetrations in a house are sealed really well is key.
This sounds easy, but it can be difficult, and the approach for each type of wall is different. The most critical detail is that the Contractor needs to be on board to give careful attention to this feature.
It's so important that most contractors assign an “air tightness” manager on site to continue to manage, inform sub-trades, and fix any issues. And air tightness should be verified by a blower door test before the finishes go on the walls.
A good HRV can save you 97% of the heat or cooling put into your house! (Credits: The FreePress Homes)
4. HVAC & Equipment
HVAC is also an important decision and would require a whole blog post to get through the details. But a few key aspects of HVAC in high performance is a Heat Recovery Unit (HRV). This means that air that is heated (or cooled) exchanges its heat with incoming fresh air before it is exhausted outside the building. This HRV can save 80-97% of the heat you put into your building!
Generally in a true passive house, an HRV combined with heat from the sun, heat from occupants, and appliances will result in an additional heat requirement that is really low. Therefore, a few electric baseboard heaters become the most cost-effective heating system. More on HVAC at a later time!
Laundry is a big decision in a passive house may surprise you! But think about your dryer. It takes air from the house, heats it up, and dumps it straight out the vent. This vent is also a 4” hole in the wall or roof that leaks all year! So many true passive house clients choose a condensing dryer, commonly found in Europe.
However, it's not a requirement to meet passive house, but you may need to compensate in other ways.
In summary
These are the four key features, decisions, and basics of Passive Houses and how we at VELD Architect approach our work. This is a lot of technical information, and at VELD Architect, we help you understand them all so you can make the right decisions for your passive house or “pretty good” house project.