A 2,440-square foot home in Holly, Michigan, is the first in the state to be certified under the German Passivhaus standard and has been named the best energy-smart home of 2014 by Fine Homebuilding magazine.
The house was designed by Matt O'Malia and Riley Pratt of GO Logic, a Belfast, Maine, architectural and construction firm, and built by Michael Klinger of Energy Wise Homes. The two-story, three-bedroom was completed in 2012 at a cost of $205 per square foot.
As described by the owners, Maura and Kurt Jung, in Fine Homebuilding's annual HOUSES issue, the house was built in Oakland County, northwest of Detroit, in "lovely moraine uplands,"an area of oak savannas and prairie fens and marshes. "These fragile habitats have not fared well with post-settlement farming practices," they write, "widespread development, introduction of aggressive invasive plants and animals, and explosion of deer populations."
The Jungs set out to bring their land back to full health as well as build a high-performance house that would require only a fraction of the energy to heat as a conventionally built home. The house is designed as a contemporary interpretation of a traditional farmhouse.
In an exclusive interview with ProudGreenHome.com, Matt O’Malia reviews this project and his view of the Passive House movement and growing acceptance of high performance building.
Q: How did you get involved in this project in Michigan?
A: The linchpin of the process was contractor Michael Klinger of Energy Wise home. He met the clients who were searching for a way to build a Passive House.
Michael Klinger had done Passive House training and had committed himself to building that way for sustainability reasons but also because it’s the right thing to do, it’s the better building.
I’ve known Michael as a friend for many years and he knew we were doing Passive Houses and he reached out to us.
We talked to the clients and they were clearly committed to the goal of a Passive House. The beautiful thing was that Michael understood what it takes to building a passive house and knew he could build it. He knew why were doing it and wouldn’t work against us to build a conventional house.
Q: What makes a Passive House different than a standard home?
A: A Passive House is a building that’s going to reduce he energy for space heating by 90 percent. It’s a really high performance building shell. The beauty of the concept is, if you do good building shell and make it perform well and do it cost effectively, you’ll be able to reduce your heating system and mechanical systems.
Q: How different is it to build a Passive House?
A: The details are not that difficult. It’s the same skill set any good carpenter has. It’s attention to detail and that's what we tell people is, we’re not asking you to build a spaceship.
It’s exactly the same building you’ve been building but we’re going to pay attention to a few other things and we’ll tell you what those are. And, we’ll give you the support to do it. Most people they get hung up on the concept rather than the reality.
Really, they have to learn to air seal better, there’s different kind of window to install. We focus on how simple it really is.
Q: What was your approach for the building envelope?
A: To meet the Passivhaus standard for extremely low heat energy consumption, the house is designed with above-grade exterior walls nearly 20 inches thick. From the inside, they consist of a 2x6 stud wall, taped Huber Engineered Woods Zip System sheathing that serves as an air barrier, vertical 11 7/8-inch I-joist cavities filled with dense-packed cellulose, 5/8-in. fiberboard, housewrap and fiber-cement lap siding over a rain screen. The total R-value is listed at R-63.
The air barrier is buried inside the wall where it can't be compromised easily, and the vapor-permeable fiberboard sheathing allows drying toward the exterior.
Above-grade foundation walls are made with insulated concrete forms further insulated with dense-packed cellulose in a 2x4 stud wall on the inside and 6 inches of expanded polystyrene (EPS) rigid insulation on the outside (R-60). Below-grade foundation walls are insulated to R-37, and the slab is insulated with 8 inches of EPS (R-35).
The truss roof is insulated with 27 inches of loose-fill cellulose (R-100) in the hipped roof and 18 inches of blown-in cellulose (R-67) at the shed roofs. The air barrier is 1/2-inch Zip System sheathing fastened to the underside of the trusses.
Q: How well does the house perform?
A: Air tightness was tested at 0.4 air changes per hour at a pressure difference of 50 pascals, well under the Passivhaus limit of 0.6 ach50. The cost of heating should be $200 or less per year.
Q: Given the weather extremes in Michigan, what HVAC strategies did you use?
People say a totally air sealed can be a bad thing, and they’re absolutely right. It can be a bad situation unless you have an active ventilation system with heat recovery.
When you go into a building that's well ventilated with a heat recovery system, you can tell. In the middle of winter, the air quality is vastly different.
When we build a Passive House, we take the heating system out. It’s down to about 200 watts of demand, about a hair dryer in size. That’s a big savings and part of what it takes to get there is the air sealing.
We make the building as air tight as possible but instead of heating we’re going to ventilate. Heating is energy out the door, you put it in the building and it escapes; it’s a one-way street. When we change our focus from heating to ventilation, we change it to improving the comfort and air quality, we’re controlling mold and we’re making a much better interior environment.
In Michigan they have high humidity levels and the only way to deal with humidity is to use an ERV to help dehumidify the air when ventilating it.
In the summer a Passive House is like any other house, the building shell doesn’t do much, you don’t have a big temperature difference but you have humidity loads. A small heat pump is good for that.
The interesting thing with a heat pump is, in a cold climate we’re used to having a separate heating system in some cases then an air conditioning system. The peak load for the system will be the air conditioning because of the humidity.
For this house in a cold climate we’re going to size the heating system by air conditioning load, not the other way around. The heating load will be less than our AC load.
Q: Is that a different way of approaching the design?
A: It’s a funny thing, once you do this tight of a building shell, all these things you hold as truths about how you configure buildings are not truths.
Heating is always the bigger load but not in this case AC is our bigger load.
To be clear, they will use more energy total in the year for heating than AC because the heating season is so long. But the peak load, the max output of the system, will be greater for cooling than it will be for heating and that is all about humidity.
Q: What components did you choose?
A: For whole-house ventilation we used a ZehnderComfoair 350 energy recovery ventilator, and for heating and cooling there are two separate 12,000 Btu/h Mitsubishi minisplit heat pumps with wall-mounted cassettes, one on the first floor and one on the second floor.
Q: Windows are such an important part of the Passive House structure – what approach did you take there?
A: We used triple-glazed windows that are the aluminum-wood AHF 115P manufactured by the German company Kneer-Sud. They are turn-tilt design, which can either swing in like a casement window or tilt in. Windows have a Solar Heat Gain Coefficient of 0.5 and an average U-factor of 0.146.
Q: Why did you choose windows from Germany?
A: When we started building Passive Houses in 2008, we looked at all types of window suppliers, international and domestic.
We know from energy modeling that triple glazed is the right window to make the whole building work as a system. We looked at what our options were and we found in North America that it was a small percentage of the market and not readily used, so like any specialty item it drives the cost up.
We looked at Germany and realized about 70 percent of the windows are triple glazed. We said, Let’s go buy an average German window that happens to be triple. The window package is about the cost of a VW.
So we buy average German windows. They’re beautiful products but they’re just not that expensive relative to domestic products. They’re built for durability, they perform well they’re easy to adjust and maintain. They don’t require any finish maintenance, they’re aluminum clad, good for 50 years. Once we figured out how to do it, we provide windows for all our projects.
Q: Do you see the interest in Passive House growing?
A: The Jung’s house winning this award will help people see that this is the kind of house they want. They can have a small heating bill and a comfortable house that doesn't have to look any different than any house out there.
One of the reasons people don’t want to live in a high performance house is they think that it will be a box and have no soul. The fact is we’re trying to make these houses as engaging as any other house. The building shell doesn't limit itself to different house types, details, facades or materials.
People have a preconception they will have to give some thing up to live like this. But it’s cost competitive to build, it’s healthier, it’s saving energy compared to other options. If you buy a hybrid that gets 50 mpg, that’s a 50 percent improvement over an average car. These houses are like a 200-mpg car, that’s the kind of improvement we’re talking about in terms of efficiency and it’s possible today.
Read more about Passive House.