Sorry for the lack of updated content over the last couple of weeks! I decided that it was finally time to take the Passive House Course. I’ve been teaching sustainable design for several years on top of practicing it here at Mottram Architecture. Although I knew the principles of passive house, and I have done blower door tests on a few local passive house homes, I had yet to take the certification course myself. Like all great programs, I needed continuing education credits for my HERS certification, so I decided to take the plunge, hence my long absence. The Certified Passive House Designer course “the German version” was only offered through New York Passive House Academy in NYC! It’s a two week course that ends with a 3 hour exam. So I spent a considerable amount of time traveling back and forth between NYC and my office over the course of May. So thank you for your patience and here’s some of what I learned.
What passive house means to me is a lot of calculations, scientific data, cool but complicated construction details, and lots of integration to make sure all the parts work together. But what should passive house mean to you? Comfortable, durable, and healthy homes. Passive House, in an ideal scenario, would be able to heat a home with a small amount of electric heat added to the ventilation system. This may be possible in Germany, but unfortunately it’s not quite possible here in New England. So some adjustments are made for longer, harsher winters, and higher humidity summers. I could list all the program requirements, but I think instead I’ll give you the reasons why this is the direction we feel the building community should move.
Targeting 70-80% reduction in energy demand in homes is great. It means building them tighter, smarter, with better insulation and fewer moving parts. We are trying to simplify the usability of the systems. I don’t mean building smaller, in fact, in the passive house program, it’s actually harder to achieve the standards with smaller homes. What I mean by simplify is the elimination of large and complicated heating systems. A better air quality system that doesn’t account for fresh air being drawn in from any crack or crevice in the building envelop. And most importantly, understanding human comfort and keeping the system balanced to those comfort levels.
Everyone can understand the value of a dollar + inflation, but the added benefit to reaching passive house targets is comfort. I recently sat down with someone who mentioned that a few years ago they built a new home. After moving in they discovered, that although it was beautiful, it had all the right finishes, it was terrible to live in. They felt somewhat jaded that they spent all this money to build a wonderful home and had to deal with drafty construction and discomfort in their home. Building a home will likely be the most expensive personal purchase you make in your lifetime. Getting it right the first time can be hard.
- Thick Insulation
- Prevention of moisture migration
- Optimize the window areas and sizes
- A reliable, steady supply of fresh air
Thick Insulation: I can’t stress enough that when you build a home you should not skimp on the insulation. This is the most difficult thing to change after a home is finished. It also seems to be the first thing on the chopping block when budgets get tight. Resist the urge to change your insulation package. Not all insulation is created equal and changing the insulation package could be the difference between you loving your home and not being able to stand it. We have a range of temperature in which we are comfortable. When insulation is poorly installed, is used in the wrong application, or gets cut, the ability to keep the wall temperature warm in the winter and cool in the summer suffers. You can understand that radiators radiate heat into the space. Well the same is true in the opposite. If the wall is cold, you will radiate heat to the wall. Losing body heat makes you feel cooler and can often be confused with drafts. Our thermal comfort is directly affected by the surface temperatures around us. So poor insulation, or not enough insulation, causes us to feel uncomfortable in our homes. And on the plus side, the more insulation you have to reduce heat transfer, the less money you’ll spend to keep your home warm.
Air tightness: Houses do not need to breath. I repeat, houses do not need to breath. It is incredibly important to make sure that air moves through your home where you want and when you want. It’s critically important to control moisture inside the house, along with other toxins that are often found in our building materials, the products we use, and the smells from what we cook. Outdoor air is necessary for healthy living, but people need to breath, not buildings. Drawing air though the building construction can lead to other more serious problems like the collection of moisture within walls. Air infiltration is also an extreme source of heat loss. Every time air leave your home, it’s replaced by air from somewhere else (outside, the attic, walls, basement etc). In the wintertime, you have to re-heat every cubic volume of air that escapes. We seem to forget that the draft isn’t just letting cold air in, it’s letting warm air out, and that’s costing you money.
Prevention of moisture migration: As you can see, air tightness and moisture migration are tied very closely together. We will always have moisture within our homes. When we breath we respire moisture. When we cook we put moisture in the air. When we supply fresh air it comes with humidity from outside. Controlling the flow of that moisture, and exhausting it to the exterior, is important. When we have cold surfaces, the moisture in the air will deposit on the surface and can grow mold. When we have leaky buildings, the moisture in the air can be pushed into the wall cavities and create condensation and rot. When hot air rises and is able to escape into our attics it can condense on the inside and make us think we have roof leaks. When a hole is drilled for a chimney and not air sealed it can “rain” indoors. Controlling the moisture is so critically important.
Optimum Windows: We no longer want to live like cavemen. We want bright airy beautiful windows that take advantage of the view, let in the sunlight for light and warmth, and allow us to feel like we are outdoors without the harsh conditions. But when it comes to windows, the public is sadly mis-informed and the US is lagging behind it’s German friends. It’s actually cheaper to buy a triple pane window in Germany than it is to buy a double pane window. They have understood that an additional layer of glass keeps the surface temperature high enough to reduce thermal discomfort and condensation. When achieving the passive house certification, it’s still necessary to buy windows from Europe to meet the requirements. Tested for air infiltration (drafts), thermal bridging (component parts), and overall U-value, we are still waiting for US Manufacturers to meet all these standards. I’m not saying it’s not possible, I’m simply stating that no US manufacturers are currently approved by the standard to meet all the requirements. However, when I say the public is misinformed I mean that doing a window replacement will not save you money in your home. It’s not as simple as new windows, the true value and savings is in how they are installed. Passive house takes great care to monitor both the window itself and how it is installed. Most replacement window projects that see vast savings come from air sealing during the installation, not the window itself. The major difference in triple pane windows is the thermal comfort and reduction of condensation which cannot be attributed to performance, but can be counted in comfort.
Fresh Air: I mentioned previously that houses do not need to breath, but people do, and this is critically important. When we first started tightening our homes to improve efficiency, we didn’t know that fresh air was necessary. We created what many call “sick building syndrome”. We had mold and contamination issues that gave building science a bad name. We have since discovered that there is a ratio of fresh air needed, per person, to have healthy indoor air. If you took note above, air isn’t exactly “fresh” if you don’t control where it comes from. Having leaky drafty buildings means high heat loss, but it also means the “fresh air” for the home may come from your wet basement, your dusty attic (and let’s all admit we’ve seen a critter or two up there), or through dried out dirty cracks in our building envelope. With passive house, not only are you supplying fresh air from an intake that isn’t positioned in the attic or next to the dumpster, but you’re supplying it where you need it most. Most people work outside of the home, so when we are home we spend a majority of that time sleeping in our bedrooms. By providing fresh air to the bedrooms we can improve the quality of the space we live. We are also pre-heating the air so it is not introduced to the space at outdoor temperature. (Negative 15 in Maine in February) and capturing energy by not having to heat the incoming air. The ventilation system also extracts air from places that are high in moisture (kitchens & baths). In an ideal scenario, this will be the one piece of equipment you need in your home, and it should be simple to use and operate.
If you’re interested in the more detailed scientific data behind passive house, don’t hesitate to reach out. If you’re a passive house consultant, we’d love to connect with you! Here at MArch, we think the constant pursuit and sharing of knowledge is beneficial to everyone! We’d love to hear from you!