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Saving 80% of Your Home's Energy the 'Passive Way'--Lessons from a Recent Home Retrofit

Visit the Community Solutions website to subscribe to their newsletter, New Solutions, and to buy the book Plan C: Community Survival Strategies for Peak Oil and Climate Change by Director Pat Murphy.

Pat Murphy and his wife Faith Morgan of Community Solutions knew a little about retrofitting buildings for low-energy use when they decided to turn their small 100- year-old carriage house into an artist's studio and apartment.

After they learned how the new German "Passive House" concept can reduce energy consumption in existing buildings by up to 80 percent, they decided to find out - and share with others - how much energy they could save in their 1,000-square foot, two-story building, once used by horses and buggies.

"A Passive House is a very well insulated, virtually air-tight building that is primarily heated by passive solar gain and by internal gains from people [and] electrical equipment," according to Katrin Klingenberg of the Urbana, Illinois-based Passive House Institute U.S. With reduced energy losses, Passive Houses can be heated with an extremely small external source or none at all.

"At first I was skeptical about the Passive House concept," said Morgan, board president of Community Solutions, a non-profit in Yellow Springs, Ohio, which educates about household sector solutions for dealing with climate change and the peak and decline of world oil production.

"To not have a furnace in a house in Ohio seemed impossible," she said With the world facing the end of cheap energy as well as the prospect of catastrophic climate changes, Community Solutions believes homes that use little energy will be critical in mitigating these twin challenges. Yet conventional methods for reducing home energy use do not approach the 80 - 90 percent reduction targets of the Passive Houses, nor do they even approach the efforts made during the 1970s energy crisis. So-called "green building" and energy efficiency programs for new homes like the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) certification and the U.S. ENERGY STAR qualified homes only save, on average, about 25 - 30 percent of the energy used in a typical building, according to Community Solutions.

Linda Wigington, a manager at Affordable Comfort, Inc., another organization promoting deep energy retrofits, said, "Recently much of the emphasis for low energy homes in the US has focused on expensive mechanical and renewable systems, such as geothermal heat pumps and solar photovoltaic arrays without substantially reducing the energy load through much higher levels of insulation and air tightness."

Wigington commended Community Solutions for its effort to demonstrate the potential to focus first on load reduction. "A smaller and less expensive renewable energy system can make a bigger impact when the load is reduced first," she said. The building had never before been a living space and it had no floor, foundation, electricity, plumbing, or utilities. In some places, the structure was leaning up to 12 inches. Because of the unfinished condition of the building, German Passive House principles could be incorporated from the outset.

"It was clear at the beginning that we would need thicker walls, floors, ceilings and roofs - in essence, thickening the building envelope," said Murphy, Community Solutions' Executive Director. Rather than using conventional 2x4 single-wall construction, they built two 2x4 walls sepaated by a five- to ten-inch space, making the walls nine to fourteen inches thick. As a result, the walls had an estimated R-value, a measure of the rate heat energy is transferred through a material, of between R-30 and R-40, far exceeding the building code standard.

To minimize heat loss through the floor, they decided to build a floor on top of the existing slab. First, plastic and two inches of rigid foam were put down over the slab. On top of the foam, 2x8 floor joists were installed, supported by ledgers on the exterior walls. Fiberglass insulation was placed between the joists.

As a result of this layering the floor was raised 12 inches, which changed the ceiling height from eight and a half feet to seven and a half feet. The result was an R-value of more than R-30 for the floor, nearly three times as much as the R-11 called for in the building code. The ceiling of the first floor was also insulated to minimize both sound and heat transfer between the first and second floors. This was done to allow division of the building into two apartments and allow independent control for any HVAC systems.

Insulating the walls and ceiling proved difficult due to the limited local availability of materials and installers and the challenges of finding reliable data. "You have to get past the rumors and marketing hype," said Murphy, who is also a former builder and building software company owner. "Deep retrofits using optimum insulation are uncommon in the industry," Murphy added. "Until consumers request well-insulated houses, builders will not offer this as an option." Different types of insulation were therefore used in different walls of the house to gain experience with insulation types and methods.

On most of the walls, damp spray cellulose was applied, which doesn't settle as dry cellulose tends to do and is both fire-retardant and insect-resistant. "An advantage over spray foam is that cellulose is made from natural materials rather than petrochemicals and there is significantly less energy used in the manufacturing process," Morgan said. And it takes about the same amount of time to install as other types of insulation. Cellulose is also less expensive.

In sections of the wall deeper than 14 inches, and in the ceiling, damp spray cellulose could not be used, as it would fall out, according to the installers. Instead, dry blown-in cellulose was used in the walls, and standard fiberglass in the ceiling, which have a comparable R-value. The R-value of the ceiling ended up being about R-40.

Wigington, in her analysis of the building, suggested that an inch or two of spray foam applied on the inside surface of the exterior sheathing (between the studs) would have prevented air movement in the wall cavity, making it warmer. This would also help minimize the potential for wintertime condensation in the cavity. Other builders suggested that caulking the joint where the framing met the sheathing, or placing strips of vinyl against the exterior sheathing, would reduce air loss.

Wigington also expressed the need to pay attention to the quality of the cellulose insulation installation. "One criticism of cellulose is that it can settle over time. To prevent this it needs to be blown in at a high density," she said, adding, "One way to assess the quality of an insulation contractor is to ask them to verify the installed density of the material. If they can't do that, get a different contractor."

Good quality windows and doors were the next consideration. While the double-paned (or doubleglazed) high performance windows selected are an improvement over most windows, they were not up to Passive House standards, which call for triple-paned windows with an R-value of eight, much higher than the R-3 of most high performance windows sold in the U.S. and the ones used in the retrofit.

However, the windows chosen were made of solid vinyl, which does not transfer heat as readily as wood. The builders also insulated around the outside of the windows.

"The more windows, the more heat loss," said Chris Glaser, the contractor hired for the project.

Thus, few windows were included in the plans, especially on the north side of the building. Though placing windows for solar gain was a consideration, it proved difficult due to the location of the building and the abundance of trees on the southern exposure.

The doors were rated at R-15, much higher than standard doors, Glaser said. The dual-glazed windows in the doors also had internal shade mechanisms between the panes of glass which can be used to gain heat or prevent heat loss, depending on the season and time of day.

After creating a thick and well insulated building envelope and ensuring high quality windows and doors, Glazer focused on making the house as tight as possible to prevent any heat from leaking out of the building. Foam was sprayed in large cracks and caulk was used extensively - between the siding and the stud, around doors and windows, and wherever there were penetrations for wires, plumbing, and other ducts. In addition, aluminum taping was used on all corners and windows and the back side of the exterior siding was painted to seal the wood.

To measure the tightness of the building and to identify remaining leaks, a blower-door test was performed. A portable, calibrated fan mounted in the building's door created a pressure difference between the inside and outside of the building equal to a 20-mph wind on all sides of the building. The air leakage rate was 480 cubic feet per minute at 50 Pascals of pressure (480 cfm50). "This is the lowest reading I've had on a two-story house this size," said Bob Klahn, a Yellow Springs-based home energy consultant. "I would've expected double that."

In existing homes being addressed using a comprehensive whole house approach such as Home Performance with Energy Star, 1000 cfm/1000 square foot is a common benchmark. This house exceeded that two-fold!

However, the carriage house's measure of air tightness did not meet the Passive House standard, developed and regulated by Passive House Institute U.S. The institute requires a 1,000-square-foot building to achieve approximately 100 cfm50 or less, five times as tight.

To ensure air quality in such a tight house, an air-to-air heat exchanger, another Passive House stipulation, was installed. "Most houses get their ventilation through air leakages, which can pick up contaminants on the way," Klahn said. Air-to-air heat exchangers are a much more efficient way of bringing fresh air into the house, as the heat is transferred from the air leaving the house to the air coming in on cold days. Because of this, Passive Houses often have better indoor air quality than conventional buildings, and fewer problems with condensation and nail-popping, two problems caused by a tight house.

Still, the retrofit project had its share of challenges. A lack of early planning led to cost and time overruns. In all, the project cost around $100 per square foot and took six months of full-time work for the crew of three - aided by various subcontractors - to complete. However, that cost includes the extensive structural work as well as the plumbing, electric and utilities installation which might account for up to 25-40% of the square foot cost. Most homes would not have this additional expense in a simple retrofit.

In addition, Murphy and Morgan found it difficult to keep ahead of the builders in trying to provide information for such an innovative deep retrofit project. "Knowledge of the Passive House is scattered around the country and Europe," Murphy explained.

"We have no regrets, because we learned a lot and it will be a demonstration for what other people can do," Morgan said. "My advice to others wanting to do this is don't just start - plan first." Glaser agreed. "The more you can plan ahead, the more cost savings can be realized in the construction project," he said. Glaser suggested some interview questions for potential retrofit contractors. "Ask about the R-values for windows, walls, ceiling, and floors, the quality of the windows, and how they deal with details like small penetrations and balloon framing," he said. People also choose a contractor based upon their experience and personality, and how involved they want to be in the project. "To save money, people can do some work themselves. With coaching, they can do demolition and help with insulation and caulking," Glaser said. This could save 10 - 20 percent of the cost. Another compromise was making the house all-electric with an electric baseboard heater, which emits about twice as much carbon dioxide per million BTUs as a natural gas furnace. However, efforts were made to keep the heating load as small as possible, so this may not be a problem. In addition, photovoltaic panels could one day be installed to handle the load of the electric heater, refrigerator, stove, and other appliances.

This may be preferable to depending on natural gas, since supplies are projected to dwindle rapidly in North America over the next few decades. Glaser, who worked inside the building comfortably with just a space heater throughout the winter, estimates the building will use about 70 percent less energy than a typical 1,000-square-foot house. He suggests about 20 percent of the savings will result from the energy-efficient windows and doors, 40 percent from the new walls and their insulation, and the rest from insulating the attic and crawl space and reducing leaks.

Preliminary testing of the building showed that it was only using 12 kilowatts per day to keep it at 59 degrees Fahrenheit when the average outside temperature was 41 degrees. When the building is complete this may decrease due to fewer leaks and more appliances and body heat to keep it warm.

In addition to requiring little energy to operate, the building's construction also utilized local and recycled materials, which reduced its embodied energy. Local walnut, pecan, and hickory were used for the window trim and cabinets.

"Changing the building envelope - including the structure, windows, and doors - was the big investment," Murphy said. "Because this building will last 100 years and energy costs are unknown in just 30 years, it will be a valuable piece of property," he said. For those who are unwilling or unable to build interior or exterior walls to thicken the envelope of their homes, Murphy suggested a variety of cost effective energy retrofits, including lighting upgrades (changing to compact fluorescents or LEDs), air sealing, and insulating the wall and attic.

"We know now we can reduce the energy use of buildings by 80 - 90 percent," Morgan said. And with the growing need to reduce carbon dioxide generation and energy because of climate change and fossil fuel depletion, models like this deep energy retrofit and the Passive House will be critical, according to Morgan.

"I feel a tremendous ease because of what could be accomplished," Morgan said.