According to a 2005 report by the U.S. Energy Information Administration, buildings consume 48 percent of the energy—and over 70 percent of the electricity—used in the United States every year. This is why drastically improving our buildings’ energy usage is so important.
Passive Houses are one way to do that. I have visited half the Passive Houses in Wisconsin. One of the two. And so lately I’ve been reading about the Passive House standard, LEED standards, and net-zero energy buildings, trying to sort out these different approaches to building science. They all point more or less in the same direction—higher performance buildings—but with different methods.
Visiting the NewenHouse
I visited Sonya Newenhouse’s certified Passive House in Viroqua, Wisconsin, in late May of this year, and again yesterday. All I can say is, “Finally!” It’s a small and efficient house that works very well, yet doesn’t seem like a cave. It’s a 25’ x 25’ square with 968 square feet on two stories, without a basement. Yes, it’s less than half the size of the average American home, but it does have a semi-attached “stuga” or cabin, which is really a three-season porch with a loft and storage space, including a root cellar. And though it’s not a mandatory element, it’s the most charming space of the whole project, so I think it adds great value to the home.
- Besides living in the house, Sonya built the home, which she calls the NewenHouse, as a prototype for “superinsulated, sustainable kit homes for people who want to live lightly on the earth.” That description comes from the flyer Sonya provided when I toured the house. There’s more info here at Sonya’s blog.
- The house design and execution are a mix of clean, European design and a bit of funky recycling. The kitchen cabinets are attractive but not high-end. The floor is a smooth concrete on the main floor, and mid-grade ash upstairs. The interior doors, light fixtures, and some plumbing pieces are recycled. Sonya said she has minimized the use of toxic materials, such as VOCs. The windows, wall system, exterior doors, and insulation package, however, are high-end. These are the parts that must be well sorted out to meet Passive House standards.
Passive House standards
Those standards are rigorous, and certified houses must achieve specific results:
- airtight building shell with 0.6 or fewer air changes per hour
- annual heat requirement less than 4.75 kBtu/square foot/year
- primary energy (heating, hot water, and electricity) use less than 38.1 kBtu/square foot/year.
So what does it take to meet those standards? Passive Houses use a specific approach to achieving energy efficiency and using only 10-20% of the energy of an average American home. Here are the design principles:
- eliminate thermal bridges
- make it airtight
- specify energy- or heat-recovery ventilation
- use high-performance windows and doors
- optimize passive-solar and internal heat gains
- model energy gains and losses using the Passive House Planning Package (PHPP).
Consistent with Passive House standards, here are some important features of the NewenHouse:
- 16” thick double-wall system with dense-pack cellulose insulation
- R-54 insulation under the slab and R-90 in the attic
- no furnace or central air conditioning system
- heat-recovery ventilator
- solar hot-water system
- triple-pane windows
- 968 square feet.
- Does it work?
And how is the house performing? We had a mild winter, and Sonya reported low electric bills and a comfortable house. Not surprising, given that the Passive House standard originated in Germany and Scandinavia. But what about the hot weather performance? We’ve had a wicked hot summer here in western Wisconsin, as has most of the country. Sonya reported that the house is about 5-20 degrees cooler than the outside temperature, which is sometimes higher than she would like. Shutters or awnings of some sort would definitely help, as would exterior solar screens, especially for windows on the west facade.
Sonya emphasized that the outside temperature isn’t the predominant factor with the indoor temp—it’s the sunshine. In the winter, with an outdoor temperature of around 0 degrees Fahrenheit, and sunshine, the house stays comfortable. But in spring, for example, with an outdoor temperature of around 40 degrees Fahrenheit and cloudy skies, the house may need some backup heat after a few days. In the summer, the design and orientation minimize solar gain, and I think the challenge will be humidity in a humid climate.
The Passive House standard is focused on a tight, extremely well insulated building and minimizing the heating load. It doesn’t address water consumption, use of sustainable materials, siting, embodied energy, and so on, but LEED standards cover that. So in contrast to the LEED standard, for example, which awards points for various inputs, the Passive House standard is defined by results. And it does work. Thousands of Passive Houses have been built in Europe, and I can attest to the charm of Sonya’s house. I would live there myself.
How it performs over time is another question, but the Passive House standard does indicate that the house will require little heating or cooling, and it has fewer components that will break down and require replacement over the years, such as a furnace or air conditioner. Photovoltaics and solar water heaters, both of which are installed on this home, are simple systems and should endure at least as well as “normal” components.
Designing a Passive House
As for the method, the designer must factor in the climate at the home site to determine the heating and cooling loads, and the requirements for insulation. The software package, the Passive House Planning Package, lets the designer enter all the specifications and then calculates the necessary wall thickness, insulation, and all the rest. The process is deliberate, exacting, and eschews guesswork. If you want to add a window on the north wall, the program will calculate the effect on the entire structure. Ignore a couple details and your new house may not qualify for Passive House certification.
What’s wrong with Passive Houses? One of the frequent dings against the Passive House standard is the cost over standard building techniques. Of course, if it were easy and could be done for no cost it already would be. And the current building standards in the U.S. have a lot of room for improvement, as well, so the basic home built in this country is likely underbuilt and underinsulated. Just think if our building codes encouraged less square footage but 20% greater energy efficiency.
Anyway, if you want a certified Passive House, or the performance required at that standard, you must follow the requirements, and some of those requirements are expensive when compared to a standard house. The thick walls, insulation package, meticulous air sealing, and elimination of thermal bridging can add significant cost up front, especially if the builder is not experienced with Passive House building methods.
And though a Passive House does require some expensive components, such as triple-pane windows that may be more challenging to find in this country, it also eliminates the normal heating and cooling systems—a hefty cost saving. And you can also choose to use recycled and low-cost components and save money where those components don’t affect performance. Over time, a Passive House should cost much less to live in, though it seems that the payback time for whatever extra cost you incur would be variable.
Furthermore, the software package and standardization of design principles should make the project more efficient and thus cheaper too. I can definitely see that a builder who has built 10 Passive Houses—and has flattened the learning curve—will be able to streamline the entire building process, making it fast, efficient, and relatively economical. It’s the “custom” or non-standard projects that are slow and expensive, as designer and builder work to sort out every detail. Sonya’s kits for Passive Houses promise the speed and efficiency of most other production homes, when built by an experienced Passive House contractor. As for criticism, the developer of the Passive House concept has heard it all.
My impression of the NewenHouse
I can appreciate some of the critiques too. I’m sure it can be difficult to build a nice-looking home to the Passive House standard, in an extreme climate, that is not a basic box. But it seems to me that homes in the most extreme climates have the most to gain from those standards. Here’s one example.
And the more Passive Houses are built in the U.S., the better the designs will become. The NewenHouse is a pretty basic box, but with some nice-looking details, and I think it’s an attractive-looking house. According to Sonya, the NewenHouse cost about $175 per square foot, excluding the price of the land, but including the solar photovoltaic and solar hot water systems. I’m sure some elements of the house could be cheaper, and some could be “nicer,” or higher quality, but I think Sonya’s choices strike an appropriate balance. Most buyers of Passive Houses, especially in kit form, are not also considering a standard McMansion, I suspect, so higher building performance wins out over two-story foyers and master suites.
I think the NewenHouse, though small for many families, offers a good example of an efficient, attractive, and pretty standard-looking home that could be built anywhere. And while $175 per square foot is fairly expensive, this is a prototype so future iterations should come in cheaper, and the Passive House standards, by design, really front-load costs to avoid them later.
Does a Passive House work in milder and warmer climates?
And what about a Passive House in different climates? The jury is out on Passive Houses in hot climates. The data is just not there yet, but it’s coming. As with the northern U.S. and Canada, the potential for energy savings in just the Southern U.S. states, and desert Southwest, is massive. We need to know how well a Passive House handles high heat and high humidity, since the standards do focus on creating an airtight shell and minimizing heating load.
As for homes in mild climates, where there isn’t much heating or cooling needed, does this standard make sense? In college I lived in Santa Barbara, California. I can’t recall ever needing heat, but the high temps did reach to around 90 degrees Fahrenheit a few times. That’s a pretty dry climate, too, so we didn’t deal with much humidity. That seems like a climate where the Passive House standards don’t justify their cost. There’s little heating load, there’s a small but possibly growing need for cooling, and if you have the windows open 350 days per year, a tight envelope is money wasted.
It seems to me that the best strategy, in a mild and dry climate, would be to have plenty of insulation in the roof to resist increasing temps in hot and sunny weather, coupled with moderate insulation in the walls. Again, the wall insulation would resist temperature swings, but a simple 2×6 wall with cellulose insulation can achieve an R-20 value. That seems like plenty. And insulation is cheap and doesn’t need maintenance.
So if I were creating an energy-efficient house in a mild climate, I would use the most efficient appliances and lighting. Most rooms would have windows on two or more sides for good cross ventilation, and I would open windows and use fans to keep the rooms comfortable. Maybe this view is too simplistic, but sealing a house to the Passive House standard, then keeping the windows open most of the time, sounds absurd.
Managing humidity is another story. How do you do that without an energy-hungry air-conditioning unit? From what I’ve read, the Passive House standards don’t address it, so I’ll have to look into it further. A Passive House is clearly an improvement over a standard American home, and obviously is more challenging to build. If you live in a warm and/or humid climate, is the Passive House standard the one you want, or should you focus on LEED standards, or something else?
Ok, that’s a long post, so I’ll end it there, and get to LEED and net-zero in the future.
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