More On Passive Houses, LEED-Certified Homes, and Net-Zero Buildings

Are high performance homes viable and appropriate for the mass market? Do they provide what their builders advertise? Are they worth the effort, or is it more greenwashing?

Why do I ask that? 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 this country every year. I think that’s a result of cheap energy for so long, but things are changing. “Energy independence” is a new theme, but it’s going to be challenging in the land of oversized McMansions.

Let's hope the time for these is past.

Let’s hope the time for these is past.

We’ve been accustomed to low standards for new construction and for remodeling for so long because of cheap energy. What if, during the housing boom of the last 15 years, homeowners and builders had emphasized energy efficiency instead of flashy items? I’m thinking of things like adding massive amounts of insulation, sealing the house against air leakage, and upgrading windows, rather than Viking ranges and granite countertops and showers with multiple jets, not to mention excessive square footage.

I’m not opposed to those elements (with the exception of excessive square footage), but I do think that more rigorous standards for energy and resource efficiency are more important. We must build structures that are more sustainable, energy efficient, and resource efficient first, and then add the other elements. Simply raising the minimum standards for housing is a huge first step.

Is the Passive House standard appropriate?

In my last post I explored Passive Houses. I like the Passive House standard because it’s about designing efficiency into the home with a heavily insulated, nearly airtight envelope. It’s so well insulated that the incidental heat produced by bodies and appliances can provide all the heat needed in some climates. Even in colder climates Passive Houses dispense with a standard HVAC system in favor of a heat- or energy-recovery ventilator and a small backup heater.

The Passive House standard is defined by results, not by methods. There are three benchmarks to hit: for air-tightness, for heating, and for overall energy use. There are some principles to follow as well, such as eliminating thermal bridging, and superinsulating, but they’re a means to an end. The three benchmarks are tough to achieve, though, so you tend to see the same methods employed to reach the standards.

A Passive House in Austria shows the typical simplicity of the design.

A Passive House in Austria shows the typical simplicity of the design.

A Passive House is quite simple but not easy, and the house either hits the target or it fails to. Thousands have been built in Europe and more are underway in the U.S., where the standards are under review because of the energy load required for dehumidification. We may see the standards tweaked to address regional differences such as high humidity.

In any case, Passive Houses have shown that it’s possible to drastically cut energy use in a home—up to around 90% in some cases compared to a standard American home with a HERS rating of 100—with building design, rather than additional hardware. Passive vs. active techniques, essentially.

Other standards for improved homes exist, as well. The U.S. Environmental Protection Agency runs the Energy Star program, which requires homes to use at least 15% less energy than a home built to the 2004 International Residential code standard, which results in a HERS score of 85 or better. That’s better than nothing, but doesn’t seem very ambitious. A Passive House should score in the range of 20-30. A net-zero home scores at 0.

LEED takes a different approach

The LEED for Homes standard, in contrast to Passive House, addresses a variety of factors in building an environmentally friendly home. This standard, from the U.S. Green Building Council, aims to “promote the transformation of the mainstream homebuilding industry toward more sustainable practices. LEED for Homes is targeting the top 25% of new homes with best practice environmental features.” The standard will be updated in 2013.

LEED for Homes, which requires independent, third-party verification, focuses on eight areas: indoor air/environment, site development, site selection, water savings, materials selection, energy efficiency, resident awareness of a home’s performance, and innovation. By following the LEED for Homes approach to these factors, you can build a home that:

  • provides a healthy indoor environment with few pollutants and abundant fresh air
  • minimizes water use
  • uses more sustainable materials and uses them efficiently, minimizing waste
  • minimizes energy use
  • is sited and built so as to minimize its environmental impact, and to have efficient access to needed services, businesses, etc.
  • costs less to operate and is sustainable over the long term.

The U.S.G.B.C. has targeted the standards to the top 25% of new homes, but other groups are applying them in the mass market. This is a fantastic idea!

Habitat for Humanity in Kent County, Michigan, has committed to the LEED Gold standard of certification. That’s not as good as Passive House standards for energy use, but it is impressive, especially since Habitat homes are meant to be affordable. (I have not seen a cost/square foot or sales prices for their projects, but have asked for that information. I’ll post it when I see it.)

This page at their site provides a good summary of LEED standards with some research done by the Alliance for Environmental Sustainability. The AES reports that annual savings on electric, heat, and water should total at least $1000 per home. Other Habitat groups around the country are taking the same approach, including LEED townhomes in St. Paul, Minnesota, which I think is a great option, as not everyone wants or needs their own yard and accompanying maintenance. Plus, townhomes can be built to a higher density, making better use of buildable lots, with the potential of preserving existing open space.

I’m encouraged to see the progress LEED, Passive House, and other sustainable techniques are making in improving housing in the U.S. And while no standard can be perfect in every situation, it seems to me that the ideal house project would use the performance standards of the Passive House, and the sustainability criteria of LEED.

Next I’ll have a look at net-zero homes.

The Farmhouse Media is all about living sustainably with

  • green building
  • permaculture
  • green cities

Passive Houses, LEED standards, and Net-Zero Buildings: are They Viable for the Mass Market?

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.

The NewenHouse front facade, as seen from Hickory Street.

The NewenHouse front facade, as seen from Hickory Street.

A view of the east facade, with the main entry porch and stuga.

A view of the east facade, with the main entry porch and stuga.

The stuga provides three-season living with a small woodstove and storm/screen window system.

The stuga provides three-season living with a small woodstove and storm/screen window system.

Sonya in the garden.

Sonya in the garden.

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.
These scarlet runner beans aren't necessary for shade in high summer, but do help prevent solar gain in late summer and early fall.

These scarlet runner beans aren’t necessary for shade in high summer, but do help prevent solar gain in late summer and early fall.

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:

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.
16" thick walls make for useful windowsills.

16″ thick walls make for useful windowsills.

When you build to Passive House standards, a 400-watt heater helps to replace a furnace.

When you build to Passive House standards, a 400-watt heater helps to replace a furnace.

The heat-recovery ventilator fits into a 2nd-floor closet.

The heat-recovery ventilator fits into a 2nd-floor closet.

Here's a view of most of the main floor.

Here’s a view of most of the main floor.

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.

The Farmhouse Media is all about living sustainably with

  • green building
  • permaculture
  • green cities