By Sara Lack and Serena Kacharos Warren
What is Passive House?

Serena: Passive House is a performance standard that focuses on reducing the energy usage of buildings and through that reduction you usually get smaller heating and cooling systems which also, in turn, creates better, more comfortable homes that are highly focused on comfort for the user. The standard focuses on airtight construction super insulation, thermal bridge-free design, triple pane windows, and efficient ventilation systems which are some of the core principles, which we’ll dive into a bit more later.

Sara: Since Passive House is a performance standard, it means that field testing needs to be done to ensure compliance. There are thresholds that must be met for annual heat demand, peak heating demand, cooling demand, and airtightness.

Serena: There are multiple levels of certifications too. You can go for the basic certification, which mainly just focuses on thermal bridging and the other key principles, but then as you move up in certifications, you start dealing with additional elements like solar panels and getting energy from other resources than just the grid.

Could you dive into some of the history and the background of passive house design?

Sara: The concept started in the 1960s. There was a lot of experimentation being done with architectural design, specifically related to its influence on thermal comfort. A lot of the strategies that were experimented with can be seen in vernacular architecture. So Passive House is really not a new concept – it’s just the codification of design strategies that have been tested throughout history.

A major proponent for Passive House was Dr. Wolfgang Feist who founded the Passive House Institute (PHI) in 1996 as an independent research institute. An abundance of research was conducted in extreme climates, where they were looking to build a more thermally insulated envelope in order to keep indoor spaces at a steady temperature during the winter while also reducing energy use.

Serena: The first certified Passive House was the Saskatchewan Conservation House. The construction of this house is the first time all the key principles were incorporated and when everything got a bit more solidified. The client wanted the house to be powered off solar, but it could not store enough solar power to keep up with the energy demand of the house. So, they set out to reduce the overall energy load of the house, which today is one of the key definitions of Passive House. With that in mind, they started doing the super insulation around the entire envelope and focused on airtightness so that there wouldn’t be any air cool or hot leaking in that would waste energy. Additionally, triple-pane windows were incorporated which again limited that transfer of energy. While passive house has evolved since then, these early methods became the driving force behind achieving a Passive House performance standard.

What are the core principles of Passive Home design?

Serena: The primary one is having a high R-value and continuous insulation. R-values measure an insulating material’s resistance to conductive heat flow – the higher the R-value, the more effective the insulating material is. So, how to visualize it is by drawing a section of a house and then making sure your insulation is continuing all the way around it: the floor, the walls, the roof – or ceiling in some cases – you just need to make sure you have a closed-loop of insulation. That is the number one way to reduce heat loss and heat gains which has the biggest effects in terms of energy usage. This applies for new homes as well as passive house renovations. For renovations, continuous insulation is one of the first steps that they take towards achieving passive house.

Sara: The next core principle is a continuous air-seal layer, which I would argue is probably the biggest difference between passive house and conventional construction. In passive house, you have to have a continuous air barrier, such as a film, similar to a waterproof barrier, that keeps the air out. Similar to insulation, it requires careful detailing in order to form a closed-loop. Passive House certifiers advocate for you to print a plan or a section and then draw a red line all the way around the envelope to make sure that every single point where there is a transition has an air seal. For instance, windows, pipes, and conduit that penetrate exterior walls all need to be air sealed. These details are often missed, so by sealing them, a lot of lost energy can be saved right away.

Serena: This also improves the air quality inside; proper sealing helps prevent dust and pollutants coming in. This leads to the third principle which is to eliminate – or greatly reduce – thermal bridges. It’s hard to get to 100 percent, so we try to reduce it as much as possible, and there are actually thresholds that you have to meet for thermal bridging.

Sara: To simplify the explanation of a thermal bridge, it is anytime you have something interrupting the insulation value of the envelope. A stud, for instance, acts as a thermal bridge because it reduces the amount of insulation between the interior and exterior where it occurs. Linear thermal bridges, such as where an exterior wall meets the slab, often cause a lot of avoidable energy loss.

Serena: Basically, when you’re incorporating these high R-value elements with your windows and your insulation, there are going to be points with the air barrier that may be more difficult to seal perfectly. For example, when your slab is meeting your foundation, your wall is a connection point and it can be really hard to wrap insulation around that because there are two things meeting. Again, careful detailing and making sure that process is done correctly, and minimizing those points as much as you can is beneficial.

Sara: The fourth core principle is high-performance glazing. For the most part, this means installing triple-pane windows. However, since passive house is a performance standard, the necessary efficiency of windows varies depending on building orientation and climate zone. In general, the idea is that the glazing should be acting better than the walls. In the summer, when there is an excess of heat, you don’t want heat coming in through the windows, so you want them to have a high R-value. In the winter windows with a high R value can act in your benefit by allowing heat in, which solid walls cannot do.

Serena: The last principle is mechanical ventilation and heat recovery. Once your detailing is complete, your insulation is in, and you have an air seal, your energy usage is now lower. However, you still have to account for some energy usage. Typically, they install HRVs or ERVs which stand for Heat Recovery Ventilation systems and Energy Recovery Ventilation systems respectively. These systems are always running, consistently taking air in, filtering it, and then pumping it throughout the house. So the occupants have fresh air, clean air. It is the only mechanical system that you need in the house, and it’s way smaller than what is used in conventional builds. Also, if you’re doing a single-family home, it can require less installation time with the contractor.

How are passive homes constructed?

Serena: It really depends on where your project is located. A lot of the long-term success of passive houses is based on the information and data collected at the very beginning. You’ll need accurate weather data for your site and you’ll have to figure out solar orientation to maximize your heat gain and during the right times. Effective construction is dependent on a lot of site factors, but one of the great things about Passive House is that it there is no set way to get there, so it can be very flexible. It does not require specific materials, like wood with metal studs – you can use heavy timber or all steel beams is you so desire. The main factor is that you just have to detail and insulate the building to make sure you have that air barrier and that you meet all of their requirements and minimum threshold values for passive house. All you have to do is get a certifier out and they approve it. Then you’re Passive House certified. Overall, it is pretty flexible, which I don’t think a lot of people really consider.

Sara: Exactly. I would say the beauty of Passive House is that it’s completely dependent on climate, location, and construction type, and it varies widely to really suit whatever the project needs are. That being said, since there is not a single standard, you are often testing new details to make sure that they work. It requires a very high level of careful detailing and extensive coordination with an experienced contractor who is on board with the idea of Passive House. Passing the certification relies heavily on proper execution of the details in the field.

Serena: Another thing to note about detailing, is that there are Passive House websites that have generic or suggested instructions on details, such as wall assemblies, that are Passive House certified. They help a bit to not have to reinvent the wheel. If you use these models, you still have to focus on the connecting details and make sure that they work for your site, but they are available to help you get reach passive house requirements in a quicker way.

Are there certain areas in California or even in the broader US that have more Passive House design or construction based on their location?

Sara: The East Coast has the highest concentration of certified passive homes in the United States.

Serena: Yeah, it started in Europe and then carried over to the U.S. and so the East Coast got introduced to it first. New York is one of those main areas it was brought. There are a lot more certifiers up in that area. We both took a Passive House course and almost all of the presenters were certifiers that were from New York. However, you are able to look up on the Passive House website where all the certifiers are located, so that’s a nice resource. Generally, it is much more prevalent on the East Coast, but it is trying to be brought to the West Coast with more individuals beginning to get certified over here.

How do Passive Homes contribute to a more sustainable future? And what are the sustainable benefits of Passive Homes?

Sara: There are a lot of sustainable elements of Passive homes. To name a few, passive homes contribute to a more sustainable future by increasing the air quality for the residents. They are cost-effective. They have increased durability due to air sealing. They have low energy use by providing a long-lasting, comfortable interior temperature. They have next to no condensation risk (which also removes the risk for mold).

Serena: I think the biggest one that would contribute to a sustainable future would be reduced energy usage through the reduction of mechanical systems and not having to use as much energy.  Durability is also a big one that some people might not think of. They design passive houses so they are able to last around 100 years. Is that right, Sara?

Sara: Yes – they have a longer life span than typical construction. Since you are sealing everything in with an air barrier, in turn a lot of the mold and condensation risk is reduced. Everything lasts longer because you don’t have contaminants going through your wall and messing up the finishes or messing up the insulation. All of your materials on the inside of the building are preserved a lot better than they would be in a typical building, so in terms of sustainability, that’s huge because you are increasing the lifespan of materials and you don’t have to demo or replace things as often.

Serena: Instead of building two houses in 100 years, you can build one and maybe make some tweaks here and there. Also, like Sara said, the air quality from an occupant’s point of view is much better – there’s less dust and during wildfire season in California, you’re not going to be worried about smoke and the air quality inside your home as much.

Finally, cost-effectiveness is also important from a client perspective and even from a designer perspective. There may be a little bit more upfront cost, but over time the money that you save on the mechanical systems makes up for that.

Sara: That’s right.  It’s a passive house so you’re saving in the long-term on mechanical systems and other things that you’d traditionally have to add in. Take solar for instance: solar is great, but that is an active system, so you’re making up for energy that you are using. Solar panels are great, but if you can reduce the amount of energy you need to begin with, you don’t need as many solar panels. The idea here is to completely eliminate or greatly reduce the need for mechanical systems.

Serena: One of the big ideas from the beginnings of passive house was that moving parts break, and therefore have to be repaired and maintained. So if we can just make a stationary house, that’s better just as is, then you’re going to have fewer problems and you’ll have a more efficient house.

How does Passive House compare or relate to other sustainable design certifications or efforts?

Sara: Passive House, as we’ve mentioned, is primarily focused on thermal comfort and interior air quality. The continuous air seal largely eliminates the need for air conditioning and heating, whereas other certifications or Green Building Standards, such as LEED, are focused on a broader range of components such as getting EnergyStar rated appliances or sustainable materials. Passive House does not address the embodied carbon or the lifecycle of products therefore, it doesn’t require a specific type of insulation. If you use foam insulation, for instance, that might work well in a passive house because it has a really high R-value, but it’s not the best material in terms of embodied carbon. Passive house is definitely a great standard for thermal comfort, air quality, and developing a long-lasting building, but it’s not meant to be looked at in a silo. It’s helpful to have other certifications in mind and be looking at building components from multiple perspectives.

What should be considered before constructing a Passive House?

Serena: There a handful of things, starting with the location which we previously mentioned. Passive House is very much site based so right off the bat, when you know you want to build a passive house, you have to enter weather data points to identify what your peak heating day or your peak cooling load might be so that you can prepare for the most extreme. That is a huge factor when you’re starting out. Solar orientation and how much sun you are getting into your building is also calculated and put into the end of the end goals for Passive House. Location is a big factor – moderate climates can be a little bit easier to meet passive house standards because you have more flexibility. In New York, they often have basements, so they have to account for this whole room that’s underground and gets way colder weather. Their installations are a little bit different and I believe they use ERVs more frequently than West Coast builds or compared to climates where it’s much more moderate.

The contractor, or more broadly, having the right people on board that are going to care about the detail, is also really important. You can draw it, but it doesn’t mean that it’s going to happen in the field. If the home is not properly sealed, you’ve still done a better job in terms of thermal insulation, but if you don’t have an air seal, it’s not going to work properly. Your mechanical systems aren’t going to be able to compensate for the energy that’s lost.

Another consideration is the certifiers themselves. As we mentioned before, there are fewer on the West Coast, but Contractors and Mechanical Engineers can actually take the Passive House courses and test to get certified. If you can find people that have that certification, then right off the bat you’re on the right path, but there are also classes offered if you just want the team to just get their heads wrapped around the concept and know the importance of detailing. We both took our courses from 3C-REN and it was free. You just had to carve out the time to do it. In general, it’s good to get in contact with your certifier early on in the process if you’re trying to get certified to ensure all of the data points and calculations are completed to their satisfaction. You don’t know they need proof that you got your blower door tested two versus three times or they wanted a specific photograph or signature. It helps to make sure that you’re checking all those boxes.

Finally, the design team experience. Just as much as the contractor and the consultants need to know how important the detailing is, the designers also need to be aware of that. If it’s a designer’s first passive house project, then it’s probably going to take a bit more time, so it’s good to account for that and your budget and your timeline.

What are the common misconceptions of Passive House?

Sara: One common misconception is that Passive House is only applicable to single-family houses, which is not true. Passive House can be applied to single-family houses, multifamily projects, large buildings, commercial buildings, small buildings, retrofits, really anything. Since it’s a performance standard, it kind of varies depending on the application, but large buildings can actually greatly benefit from passive house because you have a higher volume to surface area ratio, so the thermal envelope that you’re making very energy efficient is now benefiting a larger volume.

Serena: Another misconception is that you can’t open the windows. You can. There are operable windows. The more important factor is that you want really good windows. You want triple-pane windows that have good frames so that you’re not getting thermal bridges in the, dead of winter when you don’t want cold air leaking into your house. Typically people are only going to open their windows when it’s more of a moderate temperature outside that matches what the thermal comfort zone we’re trying to get inside is, so it’s totally acceptable to open the windows.

Sara: Yet another misconception is that since you’re sealing your building, the air quality on the inside must be awful, which is also not true. Instead of breathing in the air that comes through walls with mold, you are now breathing in air that is intentionally filtered through a ventilation system. The air quality drastically increases on the inside which many do not realize.

Serena: Another myth is that passive house standards are too restrictive on aesthetics. A lot of people think that passive house is only for single-family homes that end up just like these monolithic boxes with really thick windows that you can’t open. But that design is typically due to inexperience with Passive House – since the designers are so focused on the detailing and making sure that everything is airtight and thermally insulated, pushing the design boundaries isn’t a top priority. Once designers get more comfortable with the standards, just like with any building type that you’re new to, they’ll get comfortable with it and more willing to push the boundaries. There are several examples of really unique buildings that are passive houses.

Sara: I would say that the last common misconception people encounter is that Passive House is too expensive. You may have a bit more upfront costs, especially if the entire design team is new to it and are creating all the details completely from scratch. However, the client will actually be saving money in the long run. There’s a little more labor and material cost in making building airtight and having higher insulation values and triple-pane windows, however, you’re saving a lot of money on the mechanical system and the eventual labor of that mechanical system. At the end of the day, your building is made to last longer and be more energy-efficient, so you are saving those costs as the project’s life goes on.

As young female architects and designers, what does Passive House mean to you and what got you initially interested in it?

Sara: In general, I’m just very interested in how we as architects can make buildings more sustainable. I’ve been interested in the concept for a while, but I didn’t know much about the key principles and wanted to learn more, which is why I took a course on it.  I think sustainability is really integral to our design process and the duty of architects to make sure we are designing projects to last as long as possible. A lot of what is interesting about Passive House is that it’s primarily a passive system, so you’re not relying on technology that may change over time, like a mechanical system or even the changing technology of solar panels. You’re relying on designing a quality building from the start, that’s made to last and be energy efficient throughout its lifespan.

Serena: What does passive house mean to me? I first heard about Passive House in college in our building science courses at University of Oregon. I think it from that initial introduction, it’s just seemed like an obvious step in sustainability. Like Sara said, the quality of all stationary things should be maximized so that we don’t have to compensate later on. Why not perfect the base and then add on what you need. So it initially piqued my interest then, but then I kind of lost touch with it and until I took a Passive House-specific course this past year. Again, it just solidified that we’ve had the same construction practices and building code with minimal changes for years. We haven’t raised the bar at all and it’s been so long. Passive House isn’t reinventing the wheel, which I think a lot of people tend to think. At the end of the day, it’s simply an improvement upon traditional standards.

Why do you think more people should consider passive house design? 

Serena: My first goal would be to have more people know about Passive House. I don’t think it’s really out there and the people that may have heard about it tend to think it’s a lot more difficult than it is. So just getting the word out and the correct facts out there is huge. Additionally, I view it from the lens of our mission: we’re trying to create environments people enjoy, so why not have it be the optimal temperature inside and have fresh air for the kids and the elderly people that are living in your home. I like quality. I want something that is going to be reliable for the next century. Also, buildings make up 41% of the US primary energy consumption, so if we can reduce that energy consumption while also improving the quality of buildings for its occupants, then it’s a win-win situation.

Sara: Agreed. I think more people should consider passive house for three reasons. The first is that it increases the quality of life (both from an air quality and comfort standpoint.) The second reason is that it decreases one’s carbon footprint by largely eliminating the need for heating and cooling. And finally, because it’s not a complicated or fancy system. There may be some small additional upfront costs, but it averages out and reduces maintenance costs over time.